Questions and Answers

I get lots of questions from folks who want to modify their Blues Juniors. You’ll find most of the answers on the Mods in Detail pages. I’ve added some questions that I’ve gotten via email, along with the answers. You can post additional questions here.


  1. bgropp says:

    Hey Bill,
    Very interested in potentially doing some mods on my green board ’96 model BJ amp. I’ve never done any mods to an amp and my soldering skills have been limited to guitars (pickups). I did the unthinkable and purchased a cannabis rex speaker as I read that you suggest making that be the last mod, but anyways, was wondering what mods might be worthwhile. I’m considering an OT mod, and maybe certain capacitators and what not. the line out and presence controls would also be nice, but I’d rather not have to drill too many holes or change the amp too much. What would be your suggestions. I play primarily blues, rock and funk and have both single and humbucker pups on my guitars. With my lack of skills from what’s mentioned above would I be in over my head for some of these mods on my own? I saw a mod kit on eBay with capacitators and a few other mods for around 70 bucks, not sure if any of those would be worthwhile and not sure if I”m allowed to post that link here on this site. Would really appreciate your advice and would love to give you my business.


    • bill says:

      The mods that make the most difference are the basic mods, the presence control, and the TO20 or TO20B output transformer. You can practice on a junked 1980s boom box or other printed circuit board electronics. The hardest part is desoldering. Once you’ve mastered that, you should be OK.

      If you’re nervous, you can always send the amp to me for mods.

  2. tothemax says:

    Hi Bill,
    A little new to your site, more serious now sinnce my Blues Jr. has a substantial hum issue. It’s a circa 1999 green board model I bought used about a year ago. It has always had a slight hum, but it seems to be more pronounced lately. I get the hum as soon as the amp warms up and the reverb pot seems to control the hum volume – the volume controls make no difference in the hum level (master or volume) on or off, fat switch makes no difference. I went through your tube test removing V1 & 2, then substituting the AX7’s. All of the AX7 tubes are Fender, the EL84’s are JJ. I’ve begun using this amp pretty regular now so I ordered a spare set of tubes for it.

    The shop where I bought it had replaced the volume pot (before I bought it), but it seems like a the repair was well done – it turns a little stiffer than the originals but seems to work well).

    Any advice would be appreciated…

    Love your site, very informative

    • bill says:

      Try cleaning and tightening the RCA connectors on the reverb tank. Maybe they’re loose or corroded. You may also need a new tank.

      • tothemax says:

        Will do, thanks for the quick update…

      • tothemax says:

        I checked the plugs and they look good. I may take a reading on the tank, so an article about checking for continuity. But there is one more possibility, when I was checking the reverb leads I see that the one connection is adjacent to the volume pot. This volume pot was repalced by the tech where I purchased the amp. I’m wondering if something in that repair may be causing the reverb hum. A new MOD reverb tank from Amazon is only $17 and the reviews for upgrading the tank in a JR were almost all positive. It may be an easy way to isolate the tank as the source of the hum.

        I love the upgrades that you have done with the Jr. down the road when I’m not depending on it I’d like to try them. For now I’d like to get rid of the hum if I can. As you mentioned working on the PC board is not an easy task, so I’d like to get your opinion on replacing the tank.

        Really appreciate your help on this.

      • tothemax says:


        Parts arrived and I replaced the tubes and reverb tank (with a MOD unit). Seems a little better but still has a significant hum in the reverb circuit (both volumes can be completely off). Used it last night, in a band scenario it’s OK but for practice it is annoying. The MOD reverb seems a little deeper. Do you think going with the basic green board kit will help?

        Since I’m using the amp on a regular basis I’m little hesitant to get too deep – I do really like this little amp.

        • bill says:

          If this is a stock green board, the reverb circuit is always active. It bypasses the master volume. The basic mods kit has the parts to wire it like the cream board, where it’s under the control of the master, which makes more sense. It’s also quieter.

  3. chris_fws says:


    Here is a link to a show I played on “Good Morning Texas” recently using a cream board Blues Jr that I modded with your mods! It was amazing! Let me know what you think!!!–236729601.html?fb_action_ids=10201143981267972

  4. bjnaber says:

    Hi, Bill!
    I just bought a used (but really like new) blues jr. Anyways, everything is stock and looks exactly how it should. However, when any note/chord has time to resonate there is a whooshing sound that slowly decays. My friend who referred me to you described it as microphonic. Any ideas on a course of action to fix this would be greatly appreciated!

  5. vseager says:

    Hi Bill,

    I am in the UK but am looking at buying a blues junior from the US. Some people in forums say that the voltage can be switched in the transformer quite easily between voltages, and some say that it can’t… can you shed any light on this?

    • bill says:

      The North American (US/Canada/Mexico) Blues Junior runs on 120V only. It does not have a 240V winding nor any means of converting. If you buy a US Blues Junior, you’ll have to run it with a converter or get the 240V transformer from Tube Amp Doctor in Germany.

  6. Thomasr says:


    I ran across a Fender FSR Blues junior III stealth Cannabis Rex the other day which I thought sounded very nice and sweet. I asked the retailer about the difference from a regular FBJ, but he couldn’t say more than that the exterior looked different and that it was equipped with an Eminence Canabis Rex speaker. Are there any other differences? Are there any factory special runs that involves other changes than the exterior and the speaker?

    I searched your site but couldn’t find the answer but it’s a huge site and I may have overlooked it.

    • bill says:

      Fender never changes the electronics, except to do an actual new model, such as Blues Junior III. To do so would mean recertifying the amp with UL, CSA, the EU, etc., which is an expensive proposition. All they can change is speaker, tubes, and cab covering.

  7. fishermangoose says:

    Hey, Bill.

    Thanks for the site. Though I play guitar, I come to you with a general circuit board question. I really enjoyed one of your tutorials about troubleshooting and fixing circuit board components. I am working on a DVD recorder power supply board — replaced a bulged capacitor and now getting voltage to it. But there is a wire/cable labled w10 that does not have any voltage. I heated and added more solder to the wire side and used a jump wire (cut from another good capacitor)on the opposite side to get voltage — but it is still dead. What is a “w” wire and how do I get it hot again?

    Many, many thanks!

    • bill says:

      “W” probably doesn’t signify anything more than “wire.” It’s not a special designation for signals or power. If it carries signal (low-power AC), you probably won’t see anything on your voltmeter.

      • fishermangoose says:

        Thank you, Bill. I failed to mention that all other “w” wires (about 100 in all boards) show hot on my voltage detector (screwdriver kind). Could it be an issue with the wire itself or maybe an issue with the circuits before it gets to the wire? Could the issue with the capacitor caused a prkblem? I appreciate you taking time to help me.

  8. nbcswjb says:

    Hi Bill,

    2002’ish creme board BJ.

    Just did a filter cap replacement. The three 22 Uf’s. (the larger 47 was done at another time) Anyway, turn it on to check it out (master and volume full off) and when the tubes warmed up I was hit with a full pitched squeal that then descended to a low rumble like an idling Harley. Now there is just a very loud hum. Hardly any instrument signal will get through even with the volume pots full.

    :pulled V1 and V2 no change
    :pulled V3 hum goes away so I’m guessing phase inverter stage, but I did a tube swap there and the problem remains.
    :pulled one lead from the new caps and ohm checked for a short (test was negative) and did the push and wiggle test on all of the tube and ribbon cable joints. went ahead and re-flowed solder just in case.

    Any ideas where to look next?

    Raleigh NC

    • bill says:

      Hi Bill,

      Is the output jack attached to the chassis? Are the blue and brown output transformer leads n the proper locations? Both can cause a lot of hum and noise.

      • nbcswjb says:

        Bada-bing. Ground the speaker jack and hum went away, went back through and swapped out tubes. V1 appears to be bad so I’ve got gain back and no hum. So that appears to have been the problem. I wonder what made the awful noise when I first powered it up? anyway thanks for the tips. I think I’m back in business : )

  9. ujd213 says:

    hi. i have a 2010 MIM Bjr with a greenback in it. has the GT’s, which are ok, but as i grow as a player, i am developing likes and dislikes.
    the amp is has a almost annoying jangle. i like the fender sound but this is a little much for me. i read that you recommend a sovtek 12ax7 lps for V1. i’m thinking of trying that before i invest in jj’s for everything else.
    what’s your take on that…..

    • bill says:

      Is the jangle tube-related? Do you hear ringing when you tap the tubes? Does the treble control moderate the jangly sound? The LPS will be a little warmer, more mellow-warm than the GT tube, but it’s a subtle effect, not a cure for the over-brightness of the Blues Junior. The basic mods kit is designed to address the tone balance.

  10. arnettmark says:

    I’m hoping to get some feedback from you Billm modded BJR users. I’m shopping for my first tube amp and I played a Blues Deluxe and loved the sound…it’s just a lot of amp for me. I play mostly in my home office and a few sundays a month at church. Blues & Rock. How similar will a modded BJR be to that blues deluxe tone? Looking for cleans with a little hair plus a few pedals.

    • bill says:

      The Blues Deluxe is much louder and has more clean headroom.

      • arnettmark says:

        Thanks Bill, but other than the results of more power you feel like the tonal characteristics are similar? Also, a 9v output mod to drive a few pedals would be nice. Not sure if there’s room in the box for another transformer…

        • bill says:

          Yes, the Blues Deluxe is in the same family. The BJr and BD sound more similar with my basic mods installed in the BJr. And there’s always room for an aux 120V plug, if not a 9V power supply.

  11. vinic says:

    Hi Bill,

    I’d like to be able to bypass the tonestack for flat response on my BJ III.
    – Would a simple RC HPF (22nF 400V + 220k to ground) between TP4 and TP5 would do the job correctly?
    – If I want to switch the bypass ON and OFF (both before and after tonestack) I guess I’ll get some audio bursts… What could I do to prevent that?

    Thanks in advance for your advices!

    • bill says:

      To get flat response from a Fender-style tone stack, simply turn off the bass and treble and turn up the mids all the way.

      • vinic says:

        Thank you for the hint… But I really want to make it switchable!
        I plan to use a footswitch and a relay in order to avoid to carry the audio signal through the footswitch cable.

        • bill says:

          The 22nF coupling cap should give you flat response and the 220K resistance will give you a large increase in loudness over the tone stack, since the tone stack is only 25K to ground through the mids pot. If you do your switching after the capacitors (your 22nF and the treble cap), you won’t be switching DC, so it shouldn’t pop. You may need a high resistance across your relay to help quiet switching transients, however.

          Edited: Sorry, I left out the 100K slope resistor. Your 220K resistor should still be somewhat louder.

  12. arnettmark says:

    Does anyone feel like it’s worth the extra dough to get the NOS version of the Jr? I’m looking at a couple used amps, the NOS with the Jensen will run an extra $50.

  13. CleanMAC says:

    Have you already seen a problem the JFet Q1 in the junior blues? My Fat switch does not work any more. Everything seems normal until the gate. I have zero volt when I push the switch but no variation of current on the out. I ask before ordering transistors for nothing.


    • bill says:

      The Fat JFET does fail very occasionally. I have probably replaced 8 or 10 of them. Fortunately, it is an inexpensive part.

      • CleanMAC says:

        Hoping that that’s it the problem! it is produced while I made cathode follower. I had put back the bad lamp in V1, then I put switched off the ampli without waiting that it discharged. By removing V1 and I heard a “PLOC” in the speaker.
        Anyway, I am happy to learn that it it is already produced and that it is not expensive.

  14. arnettmark says:

    Picking up a B Jr tomorrow. I’ve read through the site and have concluded the best place to start is the basic mod kit and a presence control. If a guy needed to piecemeal his way through amp mods, is that a good first step? OT for round two?

  15. Danchez says:

    Hey Bill,

    Just want you to know that I absolutely love the work you do man! I’m about to be the proud owner of a Blues Jr. NOS tomorrow and I wanted to go about the process of modding it.

    If I were to tell you that money is of no concern and I wanted to go ALL OUT with the amp in getting all the mods I could possibly get to improve the sound of the amp to the maximum — what kits would you recommend me getting? Looking forward to hearing back from you!

    • bill says:

      It depends if you want to stay with 15 watts or move up to 6L6s and 30 watts. It’s much more expensive, but it’s a whole different experience. At the stock power level, you don’t need anything more than the basic mods, presence control, and TO20B or TO20 output transformer. The rest is optional.

      • Danchez says:

        I play lead guitar often and all of my overdrive comes primarily from my pedalboard. So in my case, I’d love to move the amp up to 30 watts for the extra clean headroom (and for that new experience you mentioned). What’s that going to look like mod-kit wise? — and don’t hold back on the utility mods (standby switch, stereo footswitch jack for clean boost/fat, etc. :] ). And do you recommend 6L6s over 6V6s for the tubes? First time I’m hearing you mention them — I think I’ve heard you talk a lot about the 6V6s more so than the 6L6s.

        Lastly, I was also planning on replacing the speakers and wondered if you had an opinion on the WGS Reaper HP? I can’t afford a Celestion G12H30 right now unfortunately and I’ve read a lot of rave reviews about the Reaper when it’s inside a BJr.

        • bill says:

          I think the 6L6 conversion is a better investment than stopping at 6V6s, especially if you play out and want the additional headroom and overall volume. Although you use pedals for drive tone, the 6L6 version with the clean boost has a nice not-so-clean tone when you turn up and it pushes the 6L6s into distortion.

          I haven’t used the WGS Reaper personally, but I’ve heard great feedback from owners.

  16. mdesign says:

    Hi Bill,
    Had a diagnostic question.

    Recently added basic mod kit (green board). All installed per instructions. Tested prior and played at recent gig (2-3hrs) no problems. At the next gig after a few songs (1/2 hour amp running) it started cutting out,(like fizzling out) then would come back full then fizzle again.

    Brought home and tested it seems to be still cutting out after after it warms up – but then seem fine (intermittent)?

    Any ideas on testing or trouble shooting? I may have a bad solder on one of the orange drops or third prong of adjustable bias may not be properly soldered?


  17. mdesign says:

    Hi Bill – Following up on my last question.
    I replace the variable bias control with the old resistor at R31. Seems to be solid now. I notice when I was setting the variable bias control — if I put normal presssure on the blue adjustable bias (while adjusting) it would drop to 0 on volt meter — then build up to 2.4 volts after i took pressure off it (almost like the solder was not proper) — this led to me isolating this Mod and replacing the old resistor (I’m running the same transformer and tubes EL84 as OEM).

    This might a good case for the files?


  18. arnettmark says:

    Hum. There it is. So I use a fender mustang floor unit for effects, no modeling. I have used it through a PA, a keyboard amp, a studio monitor system and a Fender solid State amp with no troubles. However, when I plug it into my new-to-me Blue Jr I get a nasty hum. The amp is pretty quiet with the guitar plugged straight in. I tried different outlets, power strips, lights off, etc but with no change. Is the BJ particularly sensitive to impedence mismatching? Is this likely the reality of matching a tube amp with a modeling pedal or a malfunction? Any ideas would be helpful. Thanks!

    • bill says:

      I’m guessing you need something with a ground lift. Radial has some nice adapters in the Big Shot series, and they give you more features for not much more than you’d pay for a HumX.

      • arnettmark says:

        The multi-effects board has xlr outputs with a ground lift. Is there any hazard to using an xlr to TRS cable from the unit to the amp then use the ground lift switch? Just want to make sure I won’t damage anything before I try it.

        • arnettmark says:

          By the way, you are an incredible resource here and I can’t thank you enough for maintaining this site and providing help for us newbies.

        • bill says:

          No danger as long as both are properly grounded at the AC socket. I notice that Fender’s manual says to use the left unnbalanced output. I assume you’ve tried that?

          • arnettmark says:

            Thanks Bill. I tried both unbalanced outputs with similar results. Using the xlr output with an adapter does indeed solve the ground loop problem, I just wanted to make sure I wouldn’t fry the input of the junior. Thanks again.

          • arnettmark says:

            Update: I’m using an adapter with a small transformer inside that helps immensely. However, I bumped the input and found intermittent noise and rf depending on how I put pressure on the input. I’m thinking bad jack. Kit ordered. Does the metal switchcraft jack require additional shielding?

          • bill says:

            No, it doesn’t require additional shielding.

  19. arnettmark says:

    Maybe I’m alone here, the FAT switch would be more useful for me if it affected the sound a little less. Is there a value that can be changed that might dial it back a bit?

    • bill says:

      I did modify a customer’s amp to make the Fat adjustable. I replaced the original 22uF cap with an upright cap and a 2K trimpot on a small piece of circuit board, so he could dial it back to the level he liked. It worked well.

      You could also replace the 22uF cathode cap with a smaller value, but you’d have to experiment until you found a size you liked.

  20. atlynch says:

    Hi Bill,
    Thanks for all the amazing info. I recently purchased a new tweed Blues Jr III from Guitar Center. I’m looking for sounds ranging from SRV Riviera Paradise through classic rock. I’ve been able to tame the ice pick by knocking down the treble a bit, but still cannot seem to find a truly rich and creamy sound. I don’t know if I should try your basic Mod kit (I have basic soldering/electrical skills), or look for a different amp (I am still in the return period). I play a Les Paul Standard and an American SSS Strat. What do you suggest?


    • bill says:

      The Blues Junior is more about drive and grind than rich and creamy, although the best drive tones are built off the bass control, with as much mids and treble as you need, and it may not be much. You should shop around some more to see if there’s another amp that gives you the tone you’re looking for before modding it.

  21. lousaad says:

    Received my order today. Thank you Bill! One question: What order should I do the mods? I ordered:

    Cream Board Basic Kit
    Presence control
    Sparkle control
    Switchcraft input jack (Cream board)
    Audio-taper master volume control
    Clean Boost module
    Stereo footswitch jack
    22 Watt Heyboer (Cream)
    Standby switch

    Can’t wait to dive in!



    • bill says:

      Do the sparkle, presence control, and input jack towards the end of the process, so you don’t put wear and tear on the wires hanging from the board. Install the Clean Boost last, since it has to be installed on the presence control and the footswitch jack. So don’t solder the last connection, where the blue wire goes, until the main board is in place and you’re about to put the speaker/footswitch board.

  22. Nick N says:

    Hi Bill,

    Great site!!

    I was wondering if you could explain how to run the BJiii with an extension cab. There is an output jack next to the speaker jack on the chassis. Is that an ext spkr out or is it something else like a line out, foot switch etc.?



    • bill says:

      That’s not an output jack. It’s a footswitch jack so you can turn on the Fat switch remotely.

      You’ll see from my mod kits page that I offer an aux jack.

  23. jtrimble62 says:

    I have a blues junior that already had the presence knob added. Added the boost module. Doesn’t work. Wired it just like the instructions. 100% sure it’s wired correctly. Next steps?? I can send pics if needed.

  24. mrmojoguitar says:

    Hi Bill,

    I think I was an early customer, circa ’08-’09. At any rate, I would like to convert my modded (by you) BJ combo to a head and use a speaker cab. Do you offer head cabs for this amp or can you recommend anyone you’ve worked with who could do this conversion?


    Steve C., Connecticut

  25. Lhem Sevy says:

    Hi Bill,
    Love your site. One of the best I found on the web to date! Got my Blues jnr off Ebay ovr a year ago and it had been lying around unused for a long time. The reverb was great and some time later got weaker to almost none at all. I then unscrewed the reverb tank and placed it outside the amp’s cabinet. The reverb was back in full. Once I screwed it back in place, it lasted for some time and went dead again. I repeated the exercise with the same results. Now, I have it placed back in the cab but in the corner against the cabinet’s wall and so far the reverb does not fail anymore. I suspect it was originally to close to the speaker’s magnet and when under tension the springs must have eventually got stuck together or pulled by the magnet against the metal of the tank. I am no tech at all but that is how I explain to myself what was hppening. What is your take on that?

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