Modifications

Billm AudioSmall amps, big sound.

Twin-Like Clean Tone: TwinStack ModOne of the easiest mods you can do your Blues Junior is to convert the tone stack from standard operation toTwin-style operation. Heres the deal: The Twin is renowned for its bell-like clean tone. Part of that is havingenormous power and headroom on tap, but the way the tone stack is wired contributes to the bright, Twinclarity. In the Twin, you can turn the bass, middle, and treble to 1, and get no sound out of the ampallfrequencies are cut off.

The Blackface tone stack, by comparison, started out with just treble and bassand a fixed mids resistor. Nomatter how much you reduced the bass and treble, some mid-frequencies are always present. The Hot Rodseries of amps, of which the Blues Junior is a member, added a mids control, but in a nod to earlier Blackfaceamps such as the Deluxe Reverb and Princeton Reverb, turning the mids control to 1 still left a basic amount ofmids in the mix.

The surprising thing is how bassy the leftover mids are and how much they can muddy up your tone.Fortunately, its incredibly easy to modify the Blues Junior tone stack to work like the Twins. The reward isgreater tonal flexibility and cleaner, brighter cleans and more interesting distortion tones. Of course, this worksbest with the tone stack mod, replacing the wimpy values in the Blues Junior stack with premium capacitorsthat give more solid bassand mids.

This mod gives you all of your stock Blues Junior mids tones from about 4 and up on the control and fewermids, down to none, from 4 and down to 1. It opens up the possibility of an ultra-scooped tone, with just trebleand bass, as well as bass-only overdrive, which can be very effective by eliminating middle and highharmonics.

Dont get me wrongthe Twin is still the King of Clean and no 15 watt amp can pretend to be something its not.But this mod is dead easy and opens up some very nice tone possibilities. Its a popular mod on the BluesDeluxe, Hot Rod Deluxe and Deville, for the same reason. So try it!

All you have to do is connect the left and middle (looking from the back) terminals of the mids control together.This allows the mids control to fully ground out the middle frequencies. You can bend a short piece of wire andstick it into the eyelets in the back of the control. You dont even need insulation. A piece of bare wire will dofine.

You must, however, make sure that the jumper wire is not longer than the eyelets depth, otherwise it couldshort against the metal portion of the control, which would remove all of the mids. You must also take care notto overheat the control. Use a deft touch with the ironjust enough to melt the solder and fuse to both the wireand the eyelet.

This mod is shown on a cream board, but it works equally well with the green board Blues Junior.

Billm Audio Blues Junior Jr TwinStack simple tone stack mod modification http://billmaudio.com/wp/?page_id=58

1 of 16 08-May-12 12:01 AM

Just to restate one of the points above, the TwinStack will give you a noticeable improvement on any BluesJunior, but the tone stack mod brings out the best by providing more available bass and mids. With more midson tap from the tone stack, you have more available when the control is wide open, down to zero when thecontrol is at 1. So you improve on the stock tones at both ends.

When we do this mod in the shop, we bridge the center and left mids pot terminals on the back of the board. Ifyoure going to be pulling the board to install other mods, plan on doing it from the back; its faster and easier.

Heres how: First, start with a short scrap of wire that bridges the two left pins of the mids pot. A thicker clippingfrom the tone caps or power supply stiffening caps is perfect.


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Next, apply heat from your soldering iron to the middle of the wire. Add a little bit of solder if necessary to helpthe melt.


3 of 16 08-May-12 12:01 AM

All done:


4 of 16 08-May-12 12:01 AM

Comment (RSS) |

62 Comments

Dave says:March 22, 2009 at 9:19 pm

I can see the offenders on ebay selling the twin stack mod kit and when unsuspecting peoplebuy it all they will get is a little piece of wire and instructions for $15. + $3. s/h . LOL

Dave

1.

Trey Pitchford says:June 5, 2009 at 5:05 pm

Have you done this mod to any other controls? If so whats the out come

bill says:June 5, 2009 at 5:08 pm

The TwinStack jumper is not a magic fix that works on other controls in some genericway. Its specific to the mids control and changes its operation from a potentiometer to avariable resistor. Its not appropriate for any of the other controls.

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5 of 16 08-May-12 12:01 AM

marsholie says:June 17, 2009 at 6:42 pm

would be be ok to put a switch so i can go back and forth if i wanted to?


Theres no point to making the TwinStack switchable. The tone stack mod gives youmore mids overall, and the TwinStack mod gives you the ability to remove all of them. Soyou create a larger range of adjustment from none to more than stock than you hadbefore.

3.

Vin Scag says:June 21, 2009 at 10:32 am

I was very pleased at how easy this mod was to do, especially for an amateur like myself.The dialability/sound is great.I got too excited with it and opened the back of my 06 Hot Rod Deluxe to do the mod there.The C6 is right in front of the terminals on the mid and I dont imagine it can be done atthis side of the PCB.I imagine this mod should be done by a good tech who would remove the board to do it ontheother side.(a mans got to know his limitations!)

4.

frank swindells says:June 30, 2009 at 2:49 pm

Hi

Thats interesting reading

If I get my amp tec to do this on my blues junior will I have the twin sound and also the stocksound available

Cheers

Frank

bill says:July 1, 2009 at 8:43 am

If you do the TwinStack mod, it works best with the tone stack mod and power supplystiffening provided in the basic mods kit. It gives you a very broad adjustment range,from less-than-stock mids and that Twin-like clean tone to more bass and mids.

5.

Jonathan says:July 1, 2009 at 9:21 am

I got a little confused when I was doing this oneI have a 2003 cream board, but the mid potdoesnt have any pins to solder together, only eyelets. I did the solder connection on thegreen back, but do I need to do both?

Thanks

Jon

bill says:

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6 of 16 08-May-12 12:01 AM

July 1, 2009 at 12:52 pm

If you installed a jumper on the green side of the circuit board, theres no reason toconnect the eyelets together. Its two ways of doing the same thing.

frank swindells says:July 5, 2009 at 7:54 am

Hi Bill

When I bought my blues junior, last month I played it next to a new Princeton. I prefered theblues junior & half the price! Im interested in the mods but dont want to lose the sound of theamp, just to give the possbilities of extra sounds when I want them. Is that what will happenwith the mods?

Thank for for your reply on 1st July

Frank SwindellsEngland

bill says:July 5, 2009 at 6:29 pm

Most people will agree that the modded amp sounds like a Blues Junior, but the best darnBlues Junior you ever heard. Thats always been my goal. I dont try to change the basictone, but improve it.

7.

dennis says:August 20, 2009 at 10:09 pm

Which of the mods would most greatly get rid of boxiness?

bill says:August 20, 2009 at 10:28 pm

The basic mods. Thats why theyre the basic mods.

8.

don b says:August 22, 2009 at 6:01 am

I was attempting to do the TwinStack mod with PCB removed and I cant help but notice theboard in your picture is differant than mine. I have a 1998 Rev. C Green Board. Should Iignore the picture and connect the two terminals as shown?

bill says:August 24, 2009 at 7:53 am

No matter what board you have, the mids control has three terminals. If you connect thetwo terminals on the left, closest to the master volume control, youve done theTwinStack mod.

9.

walt says:September 3, 2009 at 11:36 am

will I have to undo this if I install the presence control mod?

bill says:September 3, 2009 at 3:54 pm

10.


7 of 16 08-May-12 12:01 AM

No, they have nothing to do with one another electronically. Tone-wise, they get alongjust fine.

balde says:September 14, 2009 at 2:42 pm

Hello bill,I have a DRRI amp. I modded mine with some features.one of the mods, was the inclusion of a mid pot instead of the fixed 6.8 k resistor. I replacedthat with a 25k mid pot. my question is, if i turn the pot all the way counter clockwise(minimum position) am i cutting all midrange freq like thw twin mod or am i leaving some??thank u very much for your concern

bill says:September 15, 2009 at 7:30 am

To make the TwinStack mod work, you have to connect the wiper of the mids pot to theside of the mids pot that connects to the bass pot. This allows the mids pot to bebypassed completely for super-scooped tone. It also shuts off all sound when all threetone controls are turned all the way down.

11.

Steve Austin says:October 26, 2009 at 1:52 pm

Hi Bill,Just thought I would update progress on my BJr. I did the tone stack mod, adjustable bias,power supply stiffening, twin stack mod and changed the volume control to an audio taper.The difference in sound was better but still did not make the amp gig worthy as the sound justkind of disappeared among the other guys, especially the drummer. Then I tried one morething. I switched out the stock Groove Tube power tubes for 2 Mullard EL 84s and what adifference! That one mod got rid of the the mushy tone completely and together with yourmods, this amp has become one of the best small club amps Ive ever played through, outsideof a Princeton of course. The tone can go from crystal clear with my Strat to down and dirtySkynyrd type harmonics with my Les Paul. Of course it has excellent highs and, with theMullards, some pretty decent lows now. In most clubs I never have to go above 3 and if I dowatch out for your ear drums. It does start to distort around 4. Any effects can be achievedthrough my pedals. The only thing that might improve the amp at this point would be some6L6 output tubes like the Princeton. But then if I did that and changed out the speaker I guessit would cost about the same as a real Princeton, cost wise. For no more money than I have inthis amp though (I bought it used) it sounds great and solves the issue of weight whencarrying it to a gig. Ive also recorded with it and it does a superb job there as well. Thanks forthe help.

12.

Tom Jordan says:November 1, 2009 at 1:34 pm

Bill,

Got the parts today, did the work and just finished test driving the Blues Jr. Youre right, themod opens up the tone of this amp fantasically! It went from that tone that some call boxy ormuffled (to me, it made my Tele sound like a Strat in switch position 2 or 4) and has reallyopened up. Plenty of bass and the power to project it but most importantly the ability to adjustthe tone for a wide range of choices.

My motovation for doing this mod was to be able to play my pedal steel through it for mysolo/midi and coffee shop type gigs. Before the mod, the mids were untamed and I wasntable to get a useable steel tone (E9 tuning and 18.5k single coil pickup). I put the BJ and steel

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8 of 16 08-May-12 12:01 AM

through the test this morning and was pleasantly suprized! It sounds like a mini twin reverb.High end sparkle, sufficient bass and most importantly control of the mids from none toplenty.

I will have no trouble using this for steel/Tele on my small gigs and for a no hum recordingrig. I dont think I could use it for a steel gig with a drummer (maybe brushes though ormikeddepends on the drummer) but for sure with my Tele. This Blues Jr is now a veryuseable and just the ticket for those in and out light-duty gigs.

My voltages for plates (11.74) and bias (2.42) came out just as you suggested and the modwas a fun way to spend the evening. Your instructions were very detailed and easy to follow.

This thing sounds like a Fender,

Tom

Rock Mumbles says:November 1, 2009 at 10:27 pm

A friend and I just did the tonestack capacitor mods and the twin-stack jumper mod to anewer Blues Junior. The owner liked the amp because of size and weight but thought it couldbe more like a Fender amp. He was thinking about buying a new speaker, and Id read quitea bit about Blues Juniors needing a new speaker, so that was my first inclination, but then Iremembered reading about your tone stack mods. To make a long(er) story short(er), thecombination of the tonestack and twin-stack mods made the amp sound like it was an entirelynew amplifier, it sounds like a real Fender amp now!

14.

BlueSimon says:November 10, 2009 at 12:04 pm

Bill,Im a blues harp player in China.Last year I bought a NOS Blues Junior from the States.Itsreally hard for me to fight with the feedback in gigs.Does this mod help to eliminatefeedback?Thanks.

Best RegardsBlueSimon

bill says:November 10, 2009 at 12:45 pm

Some harp players say they get better headroom before feedback with the Twinstackbecause it makes the tone controls less interactive and they can pull out more mids. Ithink that the best solution for harp is a 10-band graphic equalizer pedal. With it, you canpull down the main feedback frequency and leave the rest of your tone intact. More bandsequal more precision, but then youd need a piece of rack equipment, not a pedal.

15.

todd huber says:December 19, 2009 at 2:29 am

Bill,I did your twin stock mod today,my junior sounds really good cant wait to do your basicmods.I want to do a twin stock mod on my hotrod deluxe.Is there anything i need to knowabout flipping the circuit board to get at it.I assume every thing else is similiar to working onblues junior.Or is there a site as good as yours with illustrations.I am new to all of this.Thanxfor your help. Todd

bill says:December 19, 2009 at 1:43 pm

16.


9 of 16 08-May-12 12:01 AM

Unfortunately, the only good Hot Rod Deluxe site disappeared a few months back and itsformer host (Eastern Kentucky University) blocks access via Archive.org. So youre onyour own with the HRDx.

Mr_Wormwood says:December 22, 2009 at 4:47 pm

Bill,I did the twin stack mod, and did not notice much difference. I was careful to make the wireonly go barely into the pots holes and was also mindful of overheating of the pot. Is itpossible that I did it wrong, or is it more likely that the difference is subtle to my ear? I guesswhat I really mean is if I did do something wrong, would there be a symptom that would be soovert that I could not miss it such as amp simply does not work or explodes or something?

The mids pot does still function (if its on one and I turn it to 11 I can hear a subtle change intone) and I am sure that I put the wire in the correct holes.

I have not done any of the other mods yet but plan to, and I am just hoping that the twinstack mod is so subtle because I have not yet replaced the caps with orange drops yet.

I am very interested in your prices for mods actually done by you as well but when I sent youan email requesting prices a few weeks ago, it was not answered.Is there a way to contact you for this or should I just email you again?

Thanks for all your info, you provide a wonderful cornucopia of information fir Blues Jr ownersand we are grateful for your passion for amp modification

bill says:December 23, 2009 at 10:20 am

You can verify the correct operation of the TwinStack by turning off all three tonecontrols. If youve done it right, no sound comes out of the amp. You can then turn upthe bass and treble for a super-scooped tone.

17.

Joe says:February 20, 2010 at 8:40 pm

Hi Bill

I have a Fennder Blues Jr. (U.S. made) and want to change the 2 tone stack caps. Can Iaquire The Orange Drops Caps from yourself. If so how much $?

bill says:February 21, 2010 at 1:42 pm

The Orange Drops are part of the basic mods kit.

18.

Randy Harper says:February 24, 2010 at 5:17 pm

Wow! You are my BJ hero! I have a Limited Edition which I play a modded Nashville Tele(Duncan Hot Rods) and a PRS Custom 22 on a modern country/southern rock gig and wasgetting ready to get another amp. After this little mod and a check through my pedal boardwith both guitars I will keep using this little guy. I have a friends Japanese Mustang and shemay not get it back. It sounds very transparent in clean/fat mode.

19.

Joe feliciano says:March 1, 2010 at 2:06 pm

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10 of 16 08-May-12 12:01 AM

Ok, just got finished with the twin mod on my blues jr. This amp made me nuts all I wantedwas a clean fender tube amp that did not cost too much. $500.00 was a good price I was sohappy in the store but at home and playing with the band it sucked: flab flab flab. so I put in aTexas heat and it was a little better. Then the tubes. If you ask me, GTs are crap anyway, so Iput in some JJs power tubes, electro hamonix pre amp tubes: 12at 12ax 12ay. I do have alittle buzz now that I didnt have before, but I think thats on me and my work I can fix it sonow I have $650.00 amp and its sound is great, tone is great.

Alice Buffalo says:May 10, 2010 at 12:49 pm

Bill,

I did the Twin stack mod and the amp sounds great (no other mods done). I can actually heardifferences when I fiddle with the knobs and the highs ring. The amp is much closer to thejazzier sound Id like, and that old guitar sound like in Little Esther Phillips The Storm.

I have noticed, though, that the amp seems quieter with the mod. When I pull the wire outand dont change any settings, its louder. Is this change in volume real or apparent (becauseeverything is clearer with the mod, the amp may only seem quieter)?

Ive also noticed that the low end sustains more. I almost cant play with the fat switch onbecause the notes just keep going until I dampen them. Why would this happen? (If it makesany difference, Im using a Heritage H-516 with humbuckersexcellent guitar)

Thanks.

bill says:May 11, 2010 at 7:53 am

When you install the TwinStack jumper, youre reducing mids, so you are in fact pullingout some of the signal. The amp is a little quieter, but you can add the mids back in againwith the mids control. Or you can compensate with more volume or more bass and trebleif you want scooped tone. With the jumper in place, youve separated the interactionbetween the mids and bass pots, so you may need to turn the bass down a bit, especiallyon a green board, so it doesnt sound too prominent.

21.

david jones says:June 10, 2010 at 3:32 pm

Hey Bill. it seems you nearly always use orange caps .what do you think of other types such as SOZO mustard caps ?


I dont hear a difference. The Orange Drop model I use is film-and-foil construction, likemost other premium caps. Theyre designed for PCB mounting.

22.

Scott says:June 20, 2010 at 10:11 am

I tried this mod a couple of weeks ago, and now I can finally stop adjusting the controlsconstantly and just enjoy playing! This really gave me control over the lower mids which weremushing up the bass sound. This small mod has made me love this amp so much more.

TIP: dont let the wire be too long. It only needs to go into the eyelet a little bit before itcreates a short. I sound checked it before I soldered to make sure its right and Im glad I did

23.


11 of 16 08-May-12 12:01 AM

because the first attempt left me with no sound.

rick frost says:August 22, 2010 at 7:11 pm

Hi, will these mods work on an original blues deville? I hate the lead channel going into middletoo loud mode.Great site you have.Rick


The TwinStack sounds good on the Blues Deville. You could probably work up a versionof the cathode follower mod, too. The other mods dont apply.

24.

Randy says:August 31, 2010 at 8:10 pm

I want to do most of the mods except for a couple I dont really need, Is there a particularorder I should do them or any that conflict? I have a Jr.thats about 3-4 months old I boughtused for $250.


Blues Junior order of work, depending on the mods you ordered:

1. pull knobs2. unscrew input jack, speaker/footswitch jacks3. pull quick connect wires from power and output transformers4. unscrew circuit board5. move jack board out of the way6. pull circuit board down/out7. clip tone stack caps, presence control resistor, bias resistor8. desolder cap stubs, resistor stubs, any pots and jacks that need to come out9. desolder input jack10. drill holes in board for bias trimpot11. drill holes in board for power supply stiffening12. insert and solder new board components, not line out jack or Clean Boost.12a. remove old output transformer, install new OT (if ordered)12b. install octal output tube sockets (if ordered)13. reinstall circuit board14. mark and drill jack and presence control holes (I find its easier with the boardinstalled rather than loose, but feel free to interchange these steps).15. install presence control16. install aux/line out jack(s)16a. connect/install ohms switch if applicable17. reinstall jack board18. install input jack19. install Clean Boost20 reconnect quick-disconnects, anything else thats loose.

25.

cgt says:September 7, 2010 at 2:54 pm

Bill,

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12 of 16 08-May-12 12:01 AM

I just picked up a 2006 MIM Blues Jr, Id love to give this mod a shot, but to be honest, I amworrying about electrocution. I used to have an Epi Valve Jr half stack and had a tech do theBitmo Trio mod on it due to the cautions listed. I was told the amp could hold a charge for awhile. I am a complete novice when it comes to electronics, is this something to considerwhen doing this mod?Thanks.


Read the Removing the Circuit Board page for an explanation of how the ampself-discharges. If you have no experience soldering on printed circuit boards, Irecommend getting help from someone who does.

Ian Edwards says:October 4, 2010 at 5:30 pm

Dear Bill,Holy crap I just did the twinstack mod. Its amazing! It really evens out dissonant chords in away that I couldnt control before. I can hear now that it was some mid-low bass that youcouldnt get rid of before that was causing the problem. Anyways, thanks for the freebie!Greatly looking forward to the kits that I ordered.

27.

John Vengrouskie says:October 5, 2010 at 8:28 am

Bill,Been reading you for a wghile, the new site is grand I have a line on a Blues Jr with intent to make it My Way whatever that is.I have a Fender Supersonic that I love (absurdly loud as it can be), especially since putting aJBL G-125 in it. Itll surf, itll crunch, itll sound like a recording amp in any vein I ask it. I havea second G-125 and my thought is that it might go well in the B-jr if I can get the amps tonein that ballpark of a Deluxe/Vibrolux sorta thing. Any suggestions there?

thanks for all the writing and doing!

JV

bill says:October 5, 2010 at 9:56 am

The basic mods, TwinStack, and presence control will give you much more tonalflexibility. An upgraded output transformer will give you better tone quality. The rest isicing on the cake.

28.

cgt465 says:October 5, 2010 at 8:13 pm

Thanks again Bill, are there any mods that help the Master volume and/or the Pregain volumehave some rolloff between zero and 1 or 2? It seems to JUMP right in, very little tweak room ifI want to play it quietly.Thanks again


The volume control is already audio taper, so theres nothing else you can do to improvethe jump-up between 1 and 2. Then again, I cant imagine why youd want to set the gain

29.


13 of 16 08-May-12 12:01 AM

that low. Its better to control the loudness with the master volume. On my Mod Kitspage, I have an audio taper control for the master. It makes the loudness curve muchmore gradual.

dan smith says:October 6, 2010 at 8:52 am

Hi Bill i recently got a kit from you,the basic kit for the mim amp and the presencecontrol/twinstack mod and had it fitted by a good local amp tech and the amp initially soundedgreat but after playing loud was getting interfearance in the notes after youve played them.Ilooked at the phase invertion oscillation atricles and did the lead dress which has helped but inow seem to be getting the sound of the spring reverb in the speaker(rattlin/distortion)whichis actually is a marshall reverb that someone who had the amp before me has added,do youthink this marshall rev could be the problem??also i changed the speaker to a eminencecannabis rex after reading your articles on speakers because i play mainly jazz either with aibanez archtop or a tele with a p90,the speaker sounds great,tried it in my hrdlx as well.Sincethe mods i am getting a amazing amount of bass from the amp and have it turned down to2/3 on the amp when using neck pickup on either guitar,i wondered if i should be getting somuch bass and i know this is causing a lot of vibration within the cab and wondered if this isnormal???many thanks.Dan.

bill says:October 20, 2010 at 9:22 pm

Are your tubes fresh? 50Hz hum (UK) is often caused by worn preamp tubes. 100Hz ismore often worn output tubes or old filter capacitors. The mods give you a LOT morebass. I like bass.

30.

David Pokotylo says:November 2, 2010 at 11:51 am

I intend to do the mod using the pot jumper wir, but am wondering how much length I shouldleave on the bent piece that goes in the eyelet?You note not longer than the eyelets depth we talking 1-2 mm here?Looking forward to doing this as my first mod on the amp!

bill says:November 3, 2010 at 7:59 am

Just use enough wire to go into the eyelets. Better yet, do it on the back of the boardand do the rest of the basic mods, too! The video on the Removing the Circuit Boardpage shows you how to get to the back quickly.

31.

Pasi says:November 3, 2010 at 9:38 am

Just did the mod and wow! The change is just radical!Thank You a lot for this mod, now I get as much and little bass as I want to. I was just aboutto sell this but now this sounds like an angel!I had already changed the Celestion Gold in it and warmed the bias of the Sovteks to some75 mV:s and now I dont have words to describe how great this sweet little amp sounds!Hats off to Bill!

32.

Joel P. says:November 28, 2010 at 8:31 pm

Hi Bill,

33.


14 of 16 08-May-12 12:01 AM

After having done almost all of your mods and changed the speaker to a Canabis Rex, I mustsay the amp sounds wonderful. Since Im always searching for perfection, is it possible toremove some of low mids from the mid control? In other words, can I narrow the freq bandcontrolled by the mid pot by removing from its bottom? I usually keep the mids at 1-2 to keepa very clean sound but I like the upper midrange fullness when I bring the control up to 4-5however I find its bottom end too muddy. The Low control is fantastic especially sincechanging the preamp coupling capacitors do I dont really wanna bring it down. Thanks!


Mids are tricky. The mids cap drains midrange tones out of the circuit. A larger capdrains more mids in a broader range. A smaller cap drains fewer mids, but in a narrowerrange. My tone stack changes the mids cap from .022uF to .015uF. You might want to trya .01uF mids cap.

You did the TwinStack mod, right? Thats important for removing midbass from the stack.

Joel P. says:December 19, 2010 at 10:16 pm

Yes I did the Twinstack mod as well as the presence control, Heyboer OT. Does themid control have a bell curve or is it essentially linear? I guess what Im looking foris to raise the center frequency of the mid pot so that it affects fewer low mids. I feelthe mid control and the bass control overlap too much, as if the mid control wasvoiced a little too low in the mid-band range. If I were to take what youre saying tothe extreme, what would be left of the mids if you had an extremely small cap onthe mid control? Would the mid control do anything? would there be a fixed amountof mids left? Obviously I lack an understanding of electronics anyway, thanks a lotfor your help and your wonderful mod kits. I must have the nicest sounding BJr intown!

bill says:January 14, 2011 at 6:26 pm

The mids control drains the leftover mids out of the circuit after the basscontrol is done. A smaller mids cap will leave more mids in the circuit, it will notchange the frequency range of the control. A larger mids cap, will drain morebass out of the circuit, however.

dan smith says:December 2, 2010 at 8:52 pm

Hi Bill,i recently emailed you because after the basic mods,presence,reverb taper,twin andtonestack mods,cannabis rex speaker(nice speaker) my mexican bj has too much bass whenusing my archtop,my teles fine but obiously is much brighter,i cant get enough sensitivity inthe bass control,i have the bass control set 1-2/2.5 but its a bit of a bass on or bass off kindof thing,Can i do anyting to smooth it out like the reverb taper style?Or lower the bass orangedrop value?or have another lower gain input?If so what do you recommend?Regards.Dan.


You could put in a .047uF instead of the .1uF bass cap. On the cream board, the basscontrol is already audio taper, so theres no further advantage to be gained there. You didthe TwinStack mod, right? That pulls out the excess midbass.

34.

Wil says:35.


15 of 16 08-May-12 12:01 AM

December 16, 2010 at 7:12 am

Hello Bill,My question is simple :I bought the re-cap kit but cant remove the old caps, they are glued to the board, I readacetone could help but I didnt tried.So how do you proceed for doing that ?Thanks(Ps : The basic and presence mods are awesome !)


After you clip the leads, you can rock the old caps side to side and it will break the gluebond.


16 of 16 08-May-12 12:01 AM

400Hz 1500Hz

Starting Level 90dB 100dB

Fat Switch 99dB 107dB

Clean Boost 97dB 106dB

Both 105dB 111dB


Billm Clean Boost ModuleOne of the ongoing complaints about the Blues Junior is that it doesnt step out enough whenyoure going from rhythm playing to solo. If youre going from clean to distorted, a pedal is anexcellent solution. The Fat switch gives you a boost in loudness and a bass boost, but it isnt quiteenough to cut through the rest of the band. Putting a clean boost pedal in front of the BluesJunior is often not a good solution because the BJrs high-gain preamp stage goes into overdriveor distortion increases to unacceptable levels. The boost just isnt clean anymore when you cut inthe pedal.

The Billm Clean Boost module gives you more volume without a tone change by boosting anunder-used stage late in the Blues Junior signal chain. It takes the preamp tone and makes itlouderdrives the output tubes harder. Its one square inch, mounts right on one of the existingcircuit board retainer screws, and all the connections are done from the top of the circuit boardnoneed to remove it or get to the back side. The clean boost module adds about as much additionalloudness as the Fat switch, but without the bass boost, and it does it at any volume level, all theway up. It boosts clean signals or distorted, and doesnt change the tone. It does not suck tone oralter the Blues Juniors tone in any way when it is off. Like the Fat switch, the Clean Boostincreases the gain of one of the Blues Juniors tube stages. But unlike the Fat switch, it doesntincrease distortion or boost the bass significantly. When youre playing loud, though, it doesultimately increase output-stage distortion, which is a good thing.

The Clean Boost is designed to come on when you pull up on the presence control. It can be usedin conjunction with the Fat switch for a big boost in volume and heavier tone. If you play out, youmay prefer an additional mod that changes the footswitch jack to a stereo jack. You can then plugin a 2-button footswitch and control the Fat switch and Clean Boost independently while youreplaying. The footswitch overrides the panel settings for both the Fat switch and the pull-up on thepresence control.

The loudness boost, when combined with that of the Fat switch is dramatic. I made some testswith continuous, harmonic-rich tones, similar to what youd get from a guitar, and wired one of myBlues Juniors so I could turn the Fat and Clean Boost on and off independently.

I tested 400Hz and 1500Hz tones, starting a higher volume level with the 1500Hz tones::

As you can see, the boost is somewhat more effective at lowerfrequencies, but the 11 to 15dB of total gain is an amazingdifference. The boost remains effective even at 12 and 12 on thevolume controls (wear your earplugs!). The Blues Junior has someuntapped power hidden away in there, and the Clean Boostmodule brings it outdramatically.

Billm Audio Billm Clean Boost for Blues Junior http://billmaudio.com/wp/?page_id=105

1 of 6 08-May-12 12:18 AM

This is the Clean Boost module. Its 1 inch square and it connects to your amp in three places. Allconnections are from the top of the circuit board, so theres no need to get to the back side.

R3 is a thumbwheel trimpot that lets you adjust the amount of boost. If youre not running theboost along with the Fat switch, youll probably leave it wide open. If youre combining the Fat andClean Boost, and the jump in volume is a little too much, you can dial it back. This is probably aone-time adjustment for most users.

The Billm Clean Boost uses premium components, including a Bourns cermet trimpot for reliable,static-free operation, and a Xicon low-ESR (equivalent series resistance) capacitor for maximumefficiency. It switches in and out silently, with no pops or clicks. The active connection usesMogami low-noise coaxial. This is mixing board/studio-grade cable. The control and powerconnections are stranded, Teflon-coated wire for ruggedness and resistance to the errantsoldering iron when you install them.


2 of 6 08-May-12 12:18 AM

Heres the Clean Boost module installed in a cream board Blues Junior. The back of the board iscushioned to prevent buzzes and vibration damage.

Although shown on a cream board, it works equally well on a green board, including those withexisting Billm mods. I supply the module fully assembled and tested, with instructions and wiringoptions.

Comment (RSS) |

18 Comments

Scott Pope says:November 16, 2009 at 1:55 am

Bill, if the audio taper gain and master volume controls are both installed, is thereanything to keep from installing the clean boost and hardwiring it so its on all thetime? With the new TO20 or TO22 transformer, it seems like that would be a modyou would want on all the time if you wanted your BluesJr to hold its own withsomething like a Blues Deluxe, or a JTM45 or such on stage?


Sure, you can just ground the blue wire and itll be on all the time. Or justleave the presence control pullswitch in the up position.

1.

John says:May 9, 2010 at 7:09 pm

It does exactly what is says on the tin. Great mod!

2.

Karl says:3.


3 of 6 08-May-12 12:18 AM

August 12, 2010 at 12:57 pm

If you want to drive the output tubes harder, why not just change the resistiveattenuator that includes the master volume control? You could swap out a fewresistors; theres plenty of gain from the preamp amplifer stages.

bill says:August 15, 2010 at 2:28 pm

The boost module is more easily switchable and includes tone shaping.

EricL says:August 13, 2010 at 2:04 pm

Hello Bill.Congratulation for all your work on the fender amps and the kit you offer. Fine newweb site too.

I was wondering what makes this boost clean compared to the fat boost since thecircuit is very similar to the fat switch, but working not on the same tube.

Thanks,Eric

EricL says:August 16, 2010 at 3:23 pm

Ok, I think I got it. This is the cap in parallel with R17 (or R10 for the fatswitch) that makes the difference. The bigger, the more bass (and viceversa). Am I right ?


Instead of changing the size of the cap, the Clean Boost includes atrimpot so you can set the amount of overall boost. In this stage of theamp, there is less bass boost than what youd get in the preamp, as withthe Fat switch.

4.

Rusty Milner says:August 30, 2010 at 10:09 pm

Bill, Is it possible to make a Mod to the Fat Boost that would tame the low endwhen in use? Also for those who like the Fat Boost on all the time, can your CleanBoost be wired to the existing Foot switch?


You can de-fat the Fat switch by replacing the 22uF bypass cap that the Fatswitch turns on/off with a smaller one, perhaps 4.7uF or 2.2uF. But if the ampsounds farty on the low end, you should probably do the basic mods and

5.


4 of 6 08-May-12 12:18 AM

TwinStack to clean it up. Then decide whether the Fat switch is more useful.

I dont recommend rewiring the Fat switch to control the Clean Boost. Itsactually easier to replace the existing jack with the stereo jack kit.

Sammy Wheeler says:September 8, 2010 at 6:34 pm

Hey Bill!

Just looking through the mods you offer for the blues junior! Excellent! I was justwondering with this particular one whether I have to have the prescence controlmod, in order to put the clean boost module in? I intend to use a two buttonfootswitch to toggle between the fat/clean boost via the stereo jack kit.

Best regards,

Sammy


Yes, you can wire it directly to the footswitch.

6.

k-o-matic says:December 28, 2010 at 5:30 am

Hello,

Sorry, I dont know anything about amp construction, so this might be a dumbquestion But is it possible to convert this clean boost module into a mid boostmodule, and be able to control the amount of mid boost with the trim pot? I have acouple of D-style amps, so I am used to having the mid-boost function

Or is it possible to convert the Fat boost into a mid boost? Is that what thede-fat-ing does? (replacing the 22uF bypass cap that the Fat switch turns on/offwith a smaller one)

Thanks in advance for your reply.


Given the simplicity of the BJr circuit, its not really possible to change the Fator Clean Boost into a mid boost. Turning up the mids control all the way givesyou some extra distortion and drive, but not as much as youd ever get out ofa Dumble-style amp.

7.

scott says:February 26, 2011 at 4:28 pm

Thanks for helping my blues jr. turn into a great amp. would it be alright to wire

8.


5 of 6 08-May-12 12:18 AM

the clean boost so its on all the time. I mean- can it be like like giving the mastera 13, and 14?


Its really designed as a boost, not a permanent volume increase. But if youlove it, you could just turn it on and leave it on; it wont hurt anything.

Paul L says:March 11, 2012 at 4:04 am

Hi Bill

Till I purchase a 2 button footswitch, can I bridge tip and ring on the stereo jack tocontrol both Fat and Clean Boost with a 1 button footswitch?

bill says:March 11, 2012 at 1:14 pm

Yes, that will work, no problems.

9.


6 of 6 08-May-12 12:18 AM


Standby Switch for Blues JuniorBy popular demand! People have been asking me for years for a standby switch on theBlues Junior, and here it is. Ive seen a couple of implementations over the years, butthey typically used an on-off-on switch with standby on one side and play on theotherkind of a kludge. Also, they involved cutting into the high-voltage wiring. I dontlike creating possible points of failure.

There isnt room inside the chassis for anotherswitch next to the power switch, even if yourelocate the pilot light. Yes, you could cram acheesy little switch in there, but were talking highvoltage here, and only a heavy-duty switch willdo. Fortunately, Carling, the same company thatmakes the power switch thats in your BluesJunior, makes a clever progressive switch. It hasthree positions: off, standby, onvery logical. Instandby, the high voltage supply is cut off. Thefilament and bias supplies receive power.

The kit is super-easy to install. Theres nosoldering andif youre sensible enough to unplug

the amp before you startno danger. I supply everything you need: the switch,high-voltage wire, and a special connector, plus photo instructions. You can be back upand running in minutes.

Even though standby switches arent really necessary on low-powered amps, Ive gottasay its pretty cool! Its a handy way to mute the amp when taking a break or whenchanging guitars. And even with the Billm cooler bias, the output tubes do run evencooler on standby.

The kits are available now. Order from the Mod Kits and Services page.

The kit does not work for the Pro Junior. The switch can be adapted, but requiresremoving the circuit board and doing some soldering.

Comment (RSS) |

41 Comments

Tom says:July 5, 2009 at 8:40 am

1.

Billm Audio Billm Standby Switch for Fender Blues Junior http://billmaudio.com/wp/?page_id=327

1 of 7 08-May-12 12:05 AM

Will this Standby Switch for Blues Junior work on a peavey classic 20 amp?


Im sure you could wire up the switch to work, but the kit is specifically forBlues Juniors.

Tom Levens says:October 24, 2009 at 1:49 pm

Ive come across a bit of information that might be of interest to your internationalreaders. Ive been repairing a cream-board Blues Junior sold in the UK that hadbeen cooking its output tubes. Not only was the Bias set WAY too hot (as wasexpected) but the plate voltage was around 380V! The combination of the two wasleading to the tubes dissipating about 16W at idle toasty! In poking about, Inoticed that Fender had the export transformer wired for 230V mains, but therewas also a 240V option on the schematic. Thought Id give it a try its as simpleas swapping the white/black wire connected to S2B (on the mains switch) with theblack wire connected to P6 (on the main board next to the fuse F1). Now itsrunning cool with a B+ of346V with the bias set correctly. If Fender are shipping all Blues Juniors to the UK(and Europe?) set for 230V, Im guessing a lot of people might be running in toproblems depending on their localvoltage. So might be worth advising people to check their B+ and adjusting thetransformer if necessary.

Tom Whitwell says:April 18, 2010 at 3:54 am

Tom, I just checked my UK Blues Junior, and it was wired for 230v. Not anymore! Thanks for the tip!

Andy P says:October 5, 2010 at 9:23 am

This was true of my Hot Rod DeVille 212 as well! Its being fixed by a friend atthe moment and one of the first things we noticed when checking over theboard was the incorrect voltage due to the connections to the transformer.Now it is running with a lower B+. This sounds like a common issue

crsturmer says:February 7, 2011 at 5:45 am

Hi Tom, Thanks for this tip. To confirm, do you take the wire off S2B andput it on P6 and take the P6 wire and put it on S2B? Sorry, if Im beingsimple, I just want to be extra sure before doing this!!

2.

Don LeBlanc says:October 25, 2009 at 8:48 pm

3.


2 of 7 08-May-12 12:05 AM

Would installing this Standby switch void the warranty on a Blues Jr or are thechanges easilly reversible ?


Im sure that it would void the warranty, but it is easily reversible.

mira arnaud says:October 30, 2009 at 9:05 am

Hello,Im living in France and i will buy your standby switch. Do you give theschemat with it?

Thank you


The instructions cover the international version of the amp, too. Photographsshow how to connect it.

4.

Larry Seagle says:December 19, 2009 at 2:56 pm

Will your standby switch for the BJ, work on my PRRI?


Yes it works. Ive installed one, and its pretty cool. Unfortunately, I neglectedto write down the lengths of the connecting wires, so I cant offer it as a kituntil I get another PRRI in hand and install another.

5.

Chris says:January 8, 2010 at 6:38 pm

Would this by some chance also work Peavey Delta Blues?

Thank you!

bill says:January 12, 2010 at 11:16 am

In theory, yes. In practice, youd have to route the B+ supply to the switchand back to the board. Someone knowledgeable about the Delta Blues wouldhave to do it. The connector I supply in the kit is specific to the Blues Junior.

6.

Javi says:January 22, 2010 at 2:06 pm

This kit was super easy to install! You just have to take your time and be very

7.


3 of 7 08-May-12 12:05 AM

careful when pushing/pulling the connectors onto the PCB. I braced the PCB with afinger while I did this. Works great, excellent work Bill!

BillEvans1956 says:June 17, 2011 at 5:35 pm

Just ordered my kit! Looking forward to getting it and making the swap. Gladto hear that its straightforward. Thanks. BillShrewsburyUnited Kingdom

BillEvans1956 says:July 2, 2011 at 10:01 am

Fitted and all up & working again. Excellent piece of kit. Thanks Bill

Mike says:January 23, 2010 at 5:11 pm

Hi, will this standby switch work for Princeton Reverbs ? Thanks


The fit is very tight on a Princeton Reverb (Reissue). Im not currently offeringit as a kit, but I may do so in the future.

8.

Mike says:January 27, 2010 at 1:18 pm

Hello again,Will this switch fit / work in a blackface or silverface Princeton Reverb ? If so, howmuch is it and how can I order one ? Thanks again


Its a very tight fit in a Princeton Reverb, at least in a reissue. Im not offeringit as a kit right now. The switches I stock have push-on connectors, so youdhave to install female connectors on the appropriate leads in the PR.

9.

Carlos says:March 1, 2010 at 9:30 am

Hi!

I installed the switch while drinking a cup of coffee nursing a hangover on aSaturday morning! Easy to install and works great!

Thanks Bill!

10.

Steve Adams says:11.


4 of 7 08-May-12 12:05 AM

June 24, 2010 at 1:11 pm

Hi AllTo save any confusion thought would confirm officially voltage for UK changedfrom 240volt to 230volts(-6%,+10%) as of January 1st 2004

Geoff says:July 3, 2010 at 4:05 pm

Hi, The change of UK mains voltage from 240v to 230v is purely cosmetic. Nothinghas actually changed, theyve just shifted the error bands as shown in Stevespost. Its still effectively 240v, folks. (This is to harmonise with the rest ofEurope btw.)

12.

Adam Mackintosh says:July 4, 2010 at 2:01 am

Love this switchare the installation instructions on this site? We bought a few ofthem for the Lynda Kay band and I think someone else got my copy. Thanks cantwait to have it in. -AM


The switch kit comes with instructions, 600V-rated jumper wire with insulatedpush-ons installed, and wire ties for putting it back together neatly.

13.

NHBluesMan says:July 15, 2010 at 2:36 pm

is the middle position just not connected to anything?

Im interested in adding a switch like this to my Blackheart Handsome Devil, andim wondering if this would work on it. Thanks!


In the middle position, theres power to the heaters and to the bias, no highvoltage to the plates. Since the HD is cathode biased, you dont have to worryabout the bias. But you can wire it so that it interrupts the high voltage supplyand leaves the filaments on.

14.

Neal says:August 7, 2010 at 12:46 pm

I have the relicd version of the Blues Jr and Im wondering if my aged nut andwasher will work on the threads of this switch?


15.


5 of 7 08-May-12 12:05 AM

Yes, the nut will fit. On Relics, I also rough up the switch with sandpaperand/or a file and rub some black and brown permanent marker into thescratches to complete the rusty look. I do the same with the replacementinput jack, which uses a different-sized nut than the original.

Good luck getting the back and case screws out.

Neal says:August 31, 2010 at 12:23 am

ha, thanks Bill. Ive already done your basic mods so getting in a secondtime wont be a problem, it sounds amazing so far, I cant wait to try theTO20 tranny I also ordered

CSCAN15 says:December 30, 2010 at 11:29 am

Hi Billwant to get this and have a couple questions. With replacing the switch, doI have to worry about any voltage issues? Getting shocked? I thought it says plugand play? Shouldnt you just have to unplug the existing terminals that areconnected to the stock switch and plug them onto the new switch? Let me know.

Thanks!


You cant get shocked if the amp is unplugged.

16.

Naal says:January 15, 2011 at 6:16 pm

Hey, Bill. You woulnt happen to know if this switch works on a Vox AC4, wouldyou? The little guy needs a standby for the sake of the tubes, and I cant seem tofind one here on the interwebs. Thanks!

-Naal


No idea whether it would work on an AC4. Someone who works on themwould be able to help. If it has the same toggle-type on-off switch, that wouldbe a start.

17.

marko5702 says:April 5, 2011 at 8:00 pm

Hey Bill just installed the stand by switch, I noticed a sight pop from the on to thestandby position and even a louder pop from standby to the off position, is thisnormal?? Its quiet when flipping the switch the other way I have a cream board,does it matter which of the two white wires go to P9 or P10? Will you be making

18.


6 of 7 08-May-12 12:05 AM

any white decals SB to stick next to the switch??Thinking about doing some of your other mods, what watt solder gun should I use.For the bias control is there a proper setting or is it by what sounds good to me?Thanks Mark.

bill says:April 6, 2011 at 7:40 am

Some noise is normal when switching in our out of standby. Youre switchingAC, which goes from zero to full voltage to zero 120 times per second. If youhappen to hit it at zero, you wont hear a thing. If you hit it at full voltageyoull hear a pop. In between the two extremes, you hear less. Its nothing toworry about.

Regarding the other kits, they come with full instructions, including setting thebias.

lazarus909 says:May 4, 2011 at 8:55 am

Will this switch work with the super champ XD ? also what tubes would yourecommend for the scxd? Thanks Bill

bill says:May 4, 2011 at 1:53 pm

This switch will not work with the SCXD. I like JJ 6V6s output tubes.

19.

TP says:June 19, 2011 at 6:13 am

Some words regarding the 230-240V issue: actually most of the time the mainvoltage I measure is near to 240V (speaking of Austria, but I think its the same inmost european countries) I changed the transformer wires to 240 on my BJ a whileago to run it cooler, but my impression was: it sounds a lot softer and mushierwith a noticable loss of clean headroom. The better idea is to leave it on 230V andset the bias cooler. High B+ voltage on a tube amp is a good thing.I always check the filament voltage on my customers BJ, if its the correct 6.3V ormax 6.7V I leave the amp on 230V. Only if its much too high up to 3,8 or 3,9V it isbetter to change the transformer wiring to 240V

20.

Jazzman says:October 17, 2011 at 1:17 am

Got the switch in Friday afternoon. Followed your instructions, which wewremeticulously spelled out! My wife helped out. It took about 10 minutes and evenMr. All Thumbs had successfully installed the switch. I used the amp on tonightsjazz trio gig and really enjoyed the new standby option the switch afforded me. Itmade a sweet amp even sweeter. I used it mainly as a jazz amp and its great!Thanks Bill!

21.


7 of 7 08-May-12 12:05 AM


Fixing Simple Printed Circuit Board MistakesEvery once in a while someone installing my mods gets in over his head, or somethingjust goes wrong, and they ask me for help. I looked around on the Web for a page thatshows how to fix common printed circuit board problems, so I could refer them to it. Iwas amazed that I couldnt find such a page. So here are some examples of what not todo, and how to fix common problems when it all goes wrong.

I recently received this board for repair. The owner had attempted to install the green board reverbmod and the tone stack capacitors, and realized that he wasnt hearing any bass or midsanymore. He had removed the tone stack caps again before he sent me the board. He hadattached a weird piece of push-back wire to the cap thats half-inserted into C20 and tack-solderedit to R40, and tack-soldered the re-routed R56 to the other side of R40. Neither tack-soldering jointheld; one broke off in shipment and the other broke when I touched it. Neither would havesurvived the pounding that a combo amp gets from its speaker.

Billm Audio Fixing Simple Printed Circuit Board Mistakes http://billmaudio.com/wp/?page_id=204

1 of 16 08-May-12 12:07 AM

As you can see, three out of four of the pads for the tone stack capacitors are completely gone.This kind of damage is normally caused when youre desoldering components. The leads are bentover onto the circuit board, and if you try to lift them while any of the solder is still adhered, thepad comes off. If you work carefully, suck all of the solder off, and make sure the lead is notadhered to any part of the pad, you wont have this kind of problem.

Scorching on the board and widely-spread rosin indicates that the soldering iron was either toolarge or too hot or both.

This is nasty, but all is not lost.


2 of 16 08-May-12 12:07 AM

I cleaned the board with solvent and scraped off the excess rosin. You can see how the lower lefttrace is partially torn off, too. The missing solder pad on the upper right breaks the continuity ofthe thicker trace.


3 of 16 08-May-12 12:07 AM

The next step is to scrape around 3/8 inch of the green solder resist on the trace leading to eachmissing pad. Take light passes with the edge of a hobby knife. You want to expose the copperbelow, but not remove any of it.


4 of 16 08-May-12 12:07 AM

The next step is to tin the exposed copper. Just heat the copper enough to flow solder onto it.Dont overheat it, or you could lift the trace.


5 of 16 08-May-12 12:07 AM

Put the new components into the holes. These Orange Drop tone capacitors have heavy leads.Here you can see that I bent the lead over sharply, so that it overlaps the tinned trace. I thenheated it and applied a bit more solder, so that there was a long, smooth bond between the leadand the trace. You can hold the lead down tightly with a jewelers screwdriver. Solder wont stick toa chromed screwdriver.

After it cools, you can trim the unsoldered portion of the lead. Make sure you dont damage thetrace when you clip the lead.


6 of 16 08-May-12 12:07 AM

The upper trace that has to be connected in two directions to complete the broken circuit. Thisrequires a different approach. I twisted a piece of wire around the capacitor lead. This is a cutofffrom a thin resistorperfect for the task. Never depend on a bridge of solder to close a gap; alwaysuse a patch wire.


7 of 16 08-May-12 12:07 AM

Drop the loop over the lead and pull it tight.

There are other ways to repair printed circuit boards, such as metal-bearing ink pens that let youdraw a new trace, or copper-loaded two-part epoxy thats rugged and conducts well. Theyre OKfor repairing cracked traces, but neither is as strong as wire and solder for a long-lasting repair orfor creating an attachment point for a component lead, as Im doing here.


8 of 16 08-May-12 12:07 AM

You can also use the loop technique to create a new solder pad. Just put a loop in the end of thewire, then connect the tail to the scraped trace on the board. Make sure that the component is firmagainst the other side of the board so that theres no possibility of play through the hole. Motioncan crack the solder joint or cause the trace to peel from the board.


9 of 16 08-May-12 12:07 AM

Remember the first picture? Above is the right way to attach top-of-board mods: Crimp thecomponents or wires so you have a strong mechanical connection before you solder.

Heres the tone stack and reverb mod, all finished up. Solder has flowed nicely on the C20connection (also crimped first), and on the R40 connections. The Orange Drop caps are gluedtogether with hot melt glue to prevent vibration. Two more dots of glue hold the wire against


10 of 16 08-May-12 12:07 AM

vibration. Whenever you solder on the top side, always check the back side to make sure that youhavent loosened the back-of-board connection.

Were all set to button it back up.

Uh-oh, wait a minute! What the heck is this? Our modder decided to lower the too-hot bias byreplacing the 22K resistor in R31 with a 27K instead of going with adjustable bias. Good, buttack-soldering the 27K resistor onto the cut-off leads of the old resistor is a bad idea, especially forbias. I pulled the board again to take a look at the back sideand do the job right.


11 of 16 08-May-12 12:07 AM

Heating the stub caused it to desolder on the other side. This is a potential disaster waiting tohappen. Losing the bias voltage will certainly take out the output tubes and maybe destroy theoutput transformer as well. Dont mod onto stubs from the top of the board!!


12 of 16 08-May-12 12:07 AM

It turns out that the tack soldering job wasnt so great, either. It broke while I was removing it. Seeabove, under potential disaster.

The solder pad and trace on the back of the board were in good shape, though. With a freshresistor in there, the bias will be dependableand cooler, reducing future heat damage from theoutput tubes and improving the tone.


13 of 16 08-May-12 12:07 AM

Even arced-over, burned traces can be repaired. Damage like this can happen from a poor solderjoint at the ribbon cable or from a screen grid failure in one of the EL84s. The carbon is conductiveand it will arc again, even after youve repaired the solder joints.


14 of 16 08-May-12 12:07 AM

The solution was to create new solder pads for the plate and screen wires. I cut the trace leadingto the burnt area so there would be no possibility of further arcing or voltage leaks.

So the moral of the story is to do mods that are within your level of expertise. Learn how to solderand desolder on a broken radio. Make every fix for the ages, not something that looks marginalor is hanging on by a thread.

The ribbon cables are especially annoying to work on. If you break one connection, you have toshorten the whole cable. Then you have to get all of the leads into the holes at the same time.Like shortening one leg of a chair, things can go from bad to worse very quickly.

The basic mods to this board were done with a too-hot soldering iron, probably a cheapo plug-inwith no thermostatic control. All of them showed board damage; I had to remove all of them (tonestack, presence, etc.) and start over again.

Comment (RSS) |

One Comment

sluggo42 says:April 12, 2012 at 8:01 pm

Well, I had to take my board in to get my mistakes fixed, and get the job finished.Got her back together and wow, sounds great!I did have 3 bad caps (2003) so I replaced everything. I still need to set the bias,and then it will be donefor now lol.

1.


15 of 16 08-May-12 12:07 AM

Anyways, my point is that its not that easy to do all of this, and unless you reallyknow what youre doing with a soldering iron, I suggest just sending it in to Bill orhaving a qualified person do the job. Its TOO easy to make a mistake and screwup your CB. I contemplated attempting to mix my goofs, but figured $100 to aqualified person was worth it. I now have $360 into my bjr, and it soundsawesome. Thats tough to beat


16 of 16 08-May-12 12:07 AM


Improving Green Board ReverbMost people agree that the reverb in the early Blues Junior stinks, and most people blame it onthe short Accutronics tank. Fender heard a lot of complaints on the Fender Discussion Pagesboard, but admitted to no faults. Then, without fanfare, it totally redesigned the reverb circuit in the2001 cream board redesign. The green board circuit picks up and reinserts the signal after theMaster Volume control, so that any hum or noise in the reverb circuit is fully amplified by the powerstage. Apart from noise, this is a poor design because if you turn the master volume up or downyou change the drive to the reverb tank. This changes the proportion of the reverb in thepost-master signal, so you generally have to adjust the reverb if you make any significant changesin the master volume.

The newer circuit picks off the signal and reinserts it before the Master Volume, so the reverbchanges with everything else and the proportion of the reverb in the final mix doesnt change. Italso uses a different dual op amp, with different component values, but the circuitry is essentiallythe same.

This modification updates the green board reverb so that it picks up the signal at the same pointas the cream board and inserts it back into the signal chain at the same point before the MasterVolume. The result is much quieter reverb operation, stronger reverb, and better reverb tone.

Although Fender used a different op amp, a 4560, when they revised the circuit theres nothingintrinsically wrong with the TL072 in the green board Blues Junior. Some early fixes for the BluesJuniors reverb attempted to change either the gain or the frequency response of the reverb circuit,but these early mods have proven to be ineffective; no one does them anymore.

Billm Audio Improving Blues Junior Jr Green Board Reverb http://billmaudio.com/wp/?page_id=34

1 of 6 08-May-12 12:10 AM

I provide the proper capacitor, with the lead already attached, plus the resistor in the green boardbasic mods kit. As you can see from the photo, you simply unsolder C20, insert the free leg intothe right hole of the C20 location, and connect the other end of the lead to the right side of R40.Then replace R56 with the provided 330K resistor, running it from the top hole to the left side ofR40. Its easiest to do this while you have the tone stack caps removed or before you replace themwith the tone stack caps provided in the green board basic mods kit.

If you want to roll your own, the 470pF cap should be a 1 kilovolt (KV) ceramic because the 1KVcaps are made to a higher quality standard that affects audio performance. Alternatively, you canuse a 470pF 250V or 500V silver mica capacitor. I supply a 1KV ceramic in the basic green boardkit.

You can use the existing 470K resistor in R56, but connected across to R40, but the new one inthe kit gives you more lead length to work with..

One More StepIf you play your BJr with the volume control at 10 and higher, you are likely to hear a high, ringingtone that sounds like feedback when a guitar is plugged in. It is feedback, and its caused by thepoor layout of the old green circuit board, which has no ground planes or other shielding. Some ofthe signal from the preamp circuitry leaks back into the amp through the input jack, and causesthe feedback.

One cure is simply to shield the jack. You can use adhesive metal foil tape (not duct tape, realaluminum tape). Heres what the shielded jack looks like, and heres the pattern I cut out of thefoil. The fingers go on both sides of the threaded portion of the jack, and ground the foil againstthe inside of the top of the chassis when you reinstall the circuit board.

When I mod green board Blues Juniors, I always replace the input jack with a Switchcraft all-metalinput jack (see kits). I bypass the feedback-prone circuit board traces entirely and wire it directly tothe preamp input resistor with shielded coaxial wire. I highly recommend the Switchcraft input jackwith all green board mods.

When you get everything back together, youll find that the reverb sounds cleaner and brighter,and has virtually none of the previous sensitivity to hum. Turning up the Reverb control no longerswamps the rest of the signal; you can use its full range. The Master Volume control will now varythe amount of reverb along with the dry signal.


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18 Comments

Dieter Billinger says:January 1, 2009 at 6:31 pm

Reverb tone/distortion suggestion:I was thoroughly impressed by the improvements in my green board Woody BluesJunior, but I did find that the reverb was somewhat distorted either by signaloverload or an excess of high frequencies causing harmonic distortions in thereverb springs. I found that turning the tone down on the guitar to reduce thehighs had a dramatic effect on the cleanliness of the reverb. This lead me tobelieve that the problem was probably caused by excess highs in the reverb tankas opposed to general signal overload. It just happens to be that I didnt have a680K resistor on hand to replace R43 however I did have a 300K and a 390k onhand which I placed in series to get the needed value. (at least close enough forrock, country and blues). The junction point of these two resistors was an idealspot to try and do some tone experimenting with the reverb. I pulled out my oldcapacitance substitution box and connected it between ground the resistor junctionto see if a suitable capacitance will clean up the reverb distortion. Indeed thisproved to be very worthwhile. I found that placing a 2.2 nf cap between theresistor junction and ground provided a remarkable clean up of the reverb signalwithout a substantial loss to the reverb signal.

TP says:December 11, 2010 at 9:02 am

Thats a good suggestion. I always found the reverb of the BJr too shrill withtoo much treble . I tried a 1,5nF across R38 (cream board) to drive the reverbwith a little less high frequencies, but what I found to be even more effective:a 2,2nF cap across the reverb poti smooths out the reverb signal itself andsounds more pleasing to my ears. Anyway I left the bypass cap C23 in thecircuit, would be probably even more effect to cut that out too.BTW: I have a Limited Edition BJr with the wooden sunburst enclosure from2003, and I had to change also all power supply filter caps. Two of themleaked and shorted the supply voltage after a while.

Many thanks to you, Bill for your passion and sharing so much usefullinformation about this nice little amp

1.

Matthias Huth (Leipzig) says:February 3, 2010 at 5:13 pm

Hi Bill, Ive done the reverb kit in my 91 green board Blues Junior. I dont changedeitehr the capacitor nor the resistor. So the hum and noise is gone and all is infunction. Only in case I turn the volume to 12 the reverb will missed a bit. May beif I would use a 330K resistor instead of the 470 K (R56) the result will be better.

2.


3 of 6 08-May-12 12:10 AM

Thanks a lot. Matthias

Ron Ditty (P-strat63) says:April 27, 2010 at 10:08 pm

Hi Bill:

The reverb on my creamboard FBJr died. After replacing it with another tank, Ifound the original to be the problem. The replacement is from a 1980s MusicmanRP112-65 combo. The trouble is that now the reverb is very noisy. Unusably noisy.I dont use a lot of reverb to begin with, just enough to add life to the sound.

Is it possible that I put the wires on backwards (I dont want to swap them until Iknow that I wont damage a vintage tank.), or is this tank bad also? Which tankwould be a good replacement?

Soon, Ill be ordering the stand-by switch and your new transformer. Theres a guyon e-Bay selling matched tubes for the FBJr that Im considering, either him or theAmp Doctor.

Thanks for your help,

Ron

bill says:April 29, 2010 at 8:52 am

That tank is probably the wrong impedance for the BJr. Use the stockAccutronics 8EB2C1B tank or the replacement Ruby or MOD tank availablefrom Mojo Musical or Antique Electronics. You can also see how to repair theusual problem with the tank here: http://billmaudio.com/wp/?page_id=46.

The red wire goes towards the middle of the amp. The black is under V1.

If youre interested in improving the tone, start with the basic mods.Upgrading the transformer doesnt help much if the amp is strangled by thestock electronics. Theres no magic about where you buy your tubes. A pair ofJJ EL84s from Mojo, Tubestore, Antique Electronics, etc. are the same.Matched 12AX7s are a waste of money.

3.

Glenn Heller says:June 16, 2010 at 12:24 am

Hi Bill. After installing this reverb mod on my green board, I felt the reverbsounded more ditorted as i increased preamp overdrive (in a brittle way, not a truereflection). And still a bit noticable with pre amp down and main volume up. Uponreading the first comments by Dieter Billinger on 1/1/09 Im wondering if youvealso tried his resistor and cap mod to the reverb circuit? Upon looking for R43 onschematics it appears to say (910K) but is that a standard value? Am I looking atthe wrong resistor? Can you help clear this up?

bill says:

4.


4 of 6 08-May-12 12:10 AM

June 17, 2010 at 6:51 pm

I have not tried Dieters mod. R43 on the green board is R37 on the creamboard. Fender increased the value to 1M. The difference is not reallynoticeable.

Glenn Heller says:June 20, 2010 at 11:19 pm

Thanks Bill. I do love the re-routed pre-master reverb path making the balancemuch better while I change settings between full master and low master. Perhapsa linear pot change will be next for the reverb.

5.

Greg Mauser says:August 5, 2010 at 3:19 pm

Hi Bill,I didnt see the answer I was looking for in the previous posts. In the green boardreverb mod, can you elaborate on the difference of the reverb sound when usingthe 330Kinstead of the 470K for R56? Im asking because I put the Ruby tank in and itsounds REALLY good but my ears are not as finely tuned as yours andI have not tested at all levels yet.

Thanks so much,Greg


The 330K resistor sends a slightly stronger signal to the reverb. No tonedifference.

6.

NAUSICAA says:January 8, 2011 at 4:26 pm

Bill, is it neccessary (or at least preferable) to sheild the input jack even if I keepmy stck plastic one? Or, does it only make sense to shield the jack if its all-metal?


If you do the tone mods, definitely shield the plastic jack. Otherwise youll getinternal feedback at high volume/high treble settings.

7.

greekscramble says:October 29, 2011 at 8:21 pm

Hi Bill,Are there instructions for bypassing the reverb all together? My chicken head knobhas broken off of the reverb, and it is pinned at 12. I never use reverb, and I dontwant it.

8.


5 of 6 08-May-12 12:10 AM

Thanks in advance.


Unplug the black wire a the tank and short the center pin to the shell tabswith some thin, bare wire.

Colins says:November 2, 2011 at 3:44 pm

Hi

Just came across this page looking for information on my BJ III reverb feedbackand It kinda sounds like the same thing, feedback/distortion when the reverb is setaround 10 and above. It just seems to happen when I hit a couple high stringstogether. Is there anything similar I can do to the BJ III to quiet it down cuz itskinda ugly.

Thanks for any help!Colin


You may just have a saggy spring in your reverb tank. Try isolating the tankwith some heavy cloth. If that helps, you may want to get a reverb bag. Or itmay make more sense to have the dealer replace the tank.

9.

tim2b98 says:March 24, 2012 at 1:09 pm

Hi, Just recieved the Basic kit that came with a few extra parts that the instructionsdid not mention. I found this page and now I know what the 470pf cap and resistor(I recieved a 430k) are for. But I still dont know what the blue 100pf cap is for?Tim


On the green board, the 100pF cap goes across the leads of R19 if youreexperiencing phase inverter oscillation.

10.


6 of 6 08-May-12 12:10 AM


Removing the Circuit BoardSome techs refuse to work on printed-circuit Fenders. Its too time-consuming and frustrating. Thenewer amps were definitely not designed with serviceability in mind. I hope this guide will helpyou.

The first thing you have to do before you can do any mods to your Blues Junior is get to the backof the circuit board. You dont have to remove it completely from the amp; its more convenient, infact, if you dont. Heres what I do to open up a Blues Junior.

Remember that tube amps run at temperatures that can burn you and voltages that can kill you.Work safely, and always think before you reach into an amp for any reason.

Disclaimer:Its a shame to have to include this, but some people just like to make their problems somebodyelses problem. Although all of these mods have worked well for me, you perform them entirely atyour own risk. I do not warrant or guarantee that they will perform the same way for you or thatyou wont damage your amplifier, burn yourself, electrocute yourself, or stick an X-Acto knifethrough your palm. Tube amplifiers have components operating at high temperatures and lethalvoltages. If you dont feel comfortable doing these mods, take the amp to someone who does.

These modifications will void your warranty. Peace and music, not lawsuits.

Heres a video that demonstrates how to remove the circuit board:

Billm Audio Removing Remove Blues Junior Jr Circuit Board http://billmaudio.com/wp/?page_id=17

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And here are the older, written instructions.

1. Unplug the amp.

Pardon me for stating the obvious. Then remove the back. If the back panel binds on the sides ofthe case, you may need to loosen the two screws on the sides of the case that hold the chassis.Dont remove them; just back them out a few turns to relax the tension on the case. Heres whatyou see when you open the back:

2. Discharge the power supply capacitors.Theyre the four large gray and black tubular objects. Actually, if you turn the amp off while thetubes are warm, it will self-discharge in 20 seconds or so. Once youve turned it off, dont turn itback on. Ensure that all the stored charge is gone from the caps by touching the positive terminalof the big one to ground with an insulated jumper. The other caps are all connected together


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through resistors and will discharge any remaining charge at the same time.

3. Clip the wire ties.You need some maneuvering room, and youll also want to retwist some of the wires later for humcontrol. Be very careful not to cut or nick any of the wires.

4. Remove the knobs and input nut.The knobs are pressed onto the plastic shafts of the control pots. Pull up with even, steadypressure. If knob doesnt come off easily, hold the pot body with your other hand to reduce stresson the circuit board. If the knob really wont come up, use a pair of spoons as levers. Pad thefaceplate so you dont damage it.

5. Remove speaker/FAT jack nuts.Use a 1/2 nut driver or socket wrench to remove the nuts that hold the speaker and FAT switchjacks. The lock washers are located inside the chassis, not under the nuts.

6. Unplug the power transformer and output transformer leads.Do this before you unscrew the board. Pull up firmly and steadily on the red, brown, and blueleads while wiggling the connectors side to side. Pull the push-on end, not the wire. Note wherethey go. Theyre marked for color on the cream board, not the green board. The green, red, andbrown pairs from the power transformer are AC, theres no polarity when you reassemble. They letgo all of a suddenmake sure youre clear of the thin wires that run from the speaker jack board.Dont tear out any wires. If youre working on an older (green circuit board) BJr, also removethe pilot light. Do this by pulling gently on the petals of the white socket assembly. I use abent-jaw long-nose pliers for this. The red lens may pop off; be careful not to lose it. The whiteLED assembly will remain attached to the wires.

7. Remove the circuit board screws.Seven screws hold the circuit board. The black plastic standoffs may be stuck to the chassis. Pullgently at each standoff location to pop them free.

Now youre ready to actually maneuver the board so that you can get to the back. Move thespeaker/FAT daughterboard out of the way, letting it hang over the lower edge of the chassis.Press the output transformer and reverb (black) wires flat against the chassis. The lower edge ofthe circuit card will want to catch on these wires, so keep pressing them down as you gently movethe circuit board down far enough for the pot shafts and input jack to clear the edge of the


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chassis. Unkink the power transformer wires so that they dont resist. Keep wiggling and pressingand sliding, making sure that youre not stressing any wires. When the shafts clear the chassis,bend it out gently, lifting the lower edge of the circuit board, until it is nearly at right angles to thechassis. This will give you full access to the back of the board.

Dont pull on the big filter capacitor. Put pressure on the empty quick-connect stakes at the leftedge of the board, instead.

This is what your circuit board should look like in working position. You have full access to theback of the board. and can operate the amp in this position after you replace the red, brown, andblue output transformer wires.

For access to the component side of the board, its easier and less wear and tear to lay the ampdown on a soft cloth or carpet than to continually bend and flex the wires.

The printed circuit traces are fragile! When you solder/unsolder, keep the heat on the componentlead. Use a temperature-controlled iron. Too much heat on the board can cause the copper traceto lift and curl.

The unsuccessful mods that come to me for repair almost always have burns on the circuitboard from a too-hot iron. You CANNOT use a crappy little plug-in iron with no thermostaticcontrol! And definitely not a soldering gun!

See my mistakes page for examples of how not to do it. (I havent moved this page to the new siteyet.)

If you have difficulty, its likely to be when you unsolder the tone stack capacitors. The bent-overleads can be difficult to straighten without damaging the printed circuit. The traces and solderpads on the back of the board are rather small and

Instead, clip the capacitors from the other side and use a solder sucker to lift the solder andthe stub of the lead. Do not try to salvage the old parts by removing them intact! Its far morelikely that you will destroy the traces on your board. Flush cutters are a better choice thanstandard diagonal pliers. The picture shows the cream board tone caps, but the same technique


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works for the green board.

After youve clipped the caps, youll see that even with flush cutters, the upward force on the leadhas caused a dimple in the solder. Its best to remove the solder and the lead stub with a soldersucker, as shown here. Youll have a clean hole with no damage.

When its time to button everything up, reverse the above procedures. When you get the circuitboard back into the chassis, twist the green, red, and brown wire pairs together to reduce thepossibility of hum. Secure them with wire ties. Dress the wires so they arch over the circuit boardand back down.

Very Important!The plastic jacks for the input and FAT switch are fragile. Any attempt to tighten them snugly willstrip the threads. Just bring them up to the point where the nut stops turning by hand, then givethem a little bit more with the wrench. Be gentle.

If youve loosened the screws on the sides of the amp, dont forget to retighten them.

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5 of 17 08-May-12 12:03 AM

54 Comments

Paul says:February 11, 2009 at 1:09 pm

Bill,

If I were to get a temp adjustable iron, what temp should it be set at?


I set mine at 650 F

1.

Peter says:March 26, 2009 at 10:50 pm

Bill,

just seeking some further clarification on discharge of the capacitors before Icommence work on the amp.

You say above: 2. Discharge the power supply capacitors. Theyre the four largegray and black tubular objects. Actually, if you turn the amp off while the tubes arewarm, it will self-discharge in 20 seconds or so. Once youve turned it off, dontturn it back on.

By the bit about if you turn the amp off while the tubes are warm do you mean:1. You switch the amp off at the on-off switch on the amp itself when the tubes areHOT, or2. You firstly do as in 1 above, but then let the tubes cool down to warm, and atthat point THEN switch the mains power off, or3. Something else I havent covered.

Sorry to labor the point, but where electricity is concerned.


If the tubes are hot enough to play through and make a sound, the amp willself-discharge in 20 seconds or so when you turn it off. Running a jumperfrom ground to the + side of any of the big gray tubular capacitors is just forinsurance.

2.

Steven says:March 31, 2009 at 12:49 am

Will a solderiong iron at 770 be too much heat to do the twin stack mod?

bill says:March 31, 2009 at 11:43 am

3.


6 of 17 08-May-12 12:03 AM

As I said above, I keep mine on 650F.

Todd says:June 5, 2009 at 3:42 pm

Bill,

What type of solder

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