Bad Filter Caps in 2003-2004 BJrs

I’ve got yet another Blues Junior on the bench with bad filter caps. In this one, all three of the 22?F filter caps had leaked. The owner had sent it to me with a note requesting the usual mods, plus a rather plaintive “… and maybe you can find out why it hums while you’re in there.”

Virtually all of these failures are on rev. C (2003 or newer) cream boards, and they’re almost always the 22uF filter caps, not the larger 47uF. They’re not stressed very hard in the Blues Junior, so I think that Illinois Capacitor (the IC brand) cranked out a bad batch of caps. The leakage looks like tan foam or glue, right around the + lead of the cap. Sometimes it drips onto the circuit board.

The symptoms may include hum, buzz, or high-frequency oscillation. Or sometimes a dirty, raspy edge to the notes that just doesn’t go away. If your Blues Junior exhibits any of these symptoms, definitely check out the filter caps.

Here’s another recent example:


In the photo above,  two caps out of three have failed. The one on the left doesn’t look too bad, but it’s gone. The one in the center is worse.

If you’ve got this condition in any of the caps in your Blues Junior, you should replace all of them. And if you find this condition in your BJr, I’d appreciate it if you’d let me know–drop a post below. This is a warranty condition if your BJr is less than five years old, but if you’re planning to mod it anyway, you might as well replace the caps with better-quality caps such as Xicon or Lelon (which I use), Nichicon, or F&T.


  1. George says:

    HI! I had this problem. I repair and replace first condensator on 100mkf [100µF].


    p.s. Sorry for my english.

    • bill says:

      Yes, there’s nothing wrong with replacing the first filter cap with a 100µF cap instead of doubling the 47µF cap. The ESR (Equivalent Series Resistance) may be a bit lower with two caps, however.

      • gameforge says:

        I have a 2006 Lacquer Tweed NOS Blues Junior, and the same two caps as you have pictured above are leaking. I’ll replace all three of them.

        Since I’m now a bit nervous about these IC caps, I was going to replace the stock 47uF with another brand while also adding a second to stiffen the power supply, and this (replacing both with a 100uF) occurred to me.

        I guess I was more worried about it being longer (a 100uF is ~1cm longer than the 47’s); as for the ESR, would it make any noticeable difference being higher than the paralleled 47’s?

        Thanks Bill!

        • bill says:

          I hate leads that are bent under the caps, but I don’t know if that would be necessary in the case of the 100. You wouldn’t hear a difference between a single 100uF and two 47s, but the ESR would be lower. It’s fairly easy to mount two 47s, so you might as well just replace all three 22s and add two 47s.

  2. Dan says:

    The amp pictured is mine, it was modded last Summer. I had not noticed any symptoms of the bad caps, but your sharp eyes spotted them and we got ’em replaced before anything was evident to the ears.
    Thanks again for your dilligence in making sure these beauties sound as good as they should!


  3. Andy says:

    Hi Bill,
    my BJ is a 2003 board (already has bias mod) and the 22uF caps look OK to me – they don’t appear to be leaking anthing. However, the amp has always had an annoying AC hum even with all knobs at zero. Sounds like typical AC buzzy hum and it’s making recording with the amp a real pain. Several years ago I tried your metal plate mod but it didn’t solve the hum. I’m pressing this amp back into recording duties so my interest in getting rid of this hum has returned. Before I blindly go and replace all the 22uF caps, if you can offer any advice it would be much appreciated.

    • bill says:

      Does it make the same hum with V1, then V2 removed? Sometimes a bad tube will cause hum by allowing AC leakage from the filament to the cathode. Also, are the EL84s (V4 and V5) fresh and matched to one another? Known-good tubes are the starting point for solving most hum problems. Phase inverter oscillation can sound like buzzy hum, too.

      If you haven’t done power supply stiffening (doubling the first filter cap), you should. It halves the ripple voltage seen by the output tubes.

  4. Daniel J. says:

    That’s one more to add to the list. I have had the parts for all the mods for a year or so and just got around to doing them after my other Junior crapped out. Opened up the back and sure enough C28 is starting to go. It leaves me in a bit of a pinch as I just opened it up to put the mods on and now this. So you are saying I need to replace C25 through C28 ? most likely. I have since lost all the instructions I was sent.

    Could anyone help me out finding a supplier of quality Caps in Columbus OH ? I really need to get this thing up and running in two days, waiting for parts would be a bummer.

    Also I already have a Nichicon for the power stiffening, should I seek out the matching component or will that not really matter as long as it is a quality part ?

    Thanks Daniel J.

  5. Jeff says:

    This is a well known problem in the world of computers. A few years ago many motherboards went to digital heaven due to bad (leaking) capacitors. There’s a story that says that a stolen formula of electrolyte that wasn’t completely correct but applied however by some companies caused the caps to blow after a certain time.

    I wonder if the problem with the BJ caps is the same.

  6. stratosmacker says:

    I got a blues jr. a month ago and it sounds great. Sometimes though on certain notes there is a mechanical buzz sound and on some there is a high pitched oscillation. After pulling a microphonic tube and making the chasis as un prone to vibration as i could it is mostly better. But not totally. I saw this and it sounds alot like my problem. I looked at the caps but they are not leaking. any ideas?

    • bill says:

      You need to go through the whole amp–make sure that the tube socket springs are tight, that there are no cracked solder joints on the sockets, that the ribbon cable to the phase inverter is up at a right angle (see the PI oscillation page), that the blue wire isn’t too close to the V4 ribbon cable, that all the other tubes are good.

      If it’s a green board, shield the input jack. If you run high volume and high treble, the tone circuit can bleed over to the input–high, ringing feedback.

      Tracking down a buzz is a two-person job unless you’ve got a signal generator (a tone generator and your PC will do fine) that can produce the buzz frequency. Then you’ve got to poke, press, and prod until you find it. It could be a bad speaker, overtightened speaker bolts, a vibrating wire, filament rattle, loose components on the board….

      Finally, it’s possible that the caps can be bad even though they’re not leaking. The IC brand caps are just OK in my book, not the best.

  7. Martin says:

    Ive got bad caps in my Blues Junior. It was built in January of 2005. All the caps are being replaced by Fender under warranty. I noticed the humming getting worse over the last few months. Finally, all I could hear was a loud buzzing sound. It didn’t matter if I had the guitar plugged in or not. It also didn’t matter if the volume, reverb, etc was on or off. Same loud buzzing sound.

    • Martin says:

      Got my Blues Junior back yesterday. All three of the small caps were bad. The big one was good, but they replaced it just in case. I don’t remember it sounding this quiet in a long time. Very happy to have her back.

  8. Dan G says:

    Hi Bill,
    I am having similar problems mentioned above. When notes are played by 4th and 5th strings on 12th fret, there is a distinct hissing noise that follows. I have a new blues Jr. with cream board. Any ideas?

  9. Jimmy F says:

    Not totally pertaining to this but I had the R47 go out on me and its listed as a 470k 1/4W resistor. I am having an impossible time finding a suitable replacement and is curious if the same value but 1/2W would work the same, or add problems? Please help.

    • Jimmy H. says:

      I had the same R47 resistor go on mine. I have replaced it with a higher watt one from Mouser Electronics but I am still not getting any sound from the amp. I can hear sound only when powering down.

    • bill says:

      I emailed you about this. You’re reading the wrong schematic for your amp. Check the dates. R47 is a 2.2K 2W resistor in the power supply–on a cream board.

  10. D says:

    my filter caps went out what do you recommend? Are they included in your cream board basic kit?

    • bill says:

      I use Xicon caps in virtually all my mods and repairs. If a customer wants premium caps, I use F&T. The cream basic mods kit includes one stiffening cap, no replacement caps. A full set is inexpensive. Email me.

  11. Tom Dawson says:

    Hey Bill

    Thanks for your work with the Blues Jr It is my favorite amp now I Have a 1999 green board that has had your mods and I love it. I recently bought a NOS tweed and am waiting for your cream board mods to arrive in the mail. I opened up the back and noticed something I did not see on my green board. All of the caps have it looks like big globs of silicone underneath them Is this normal? Before I do the mods I wanted to find out so I could go back to Fender. The amp is used but only a year old and the warranty is transferable. I could send pix if you like.

    Thanks Tom

    • bill says:

      There should be globs of silicone under the four filter caps to keep them from rattling against the board and to prevent solder joint breakage from vibration. If there’s goop under all of the caps, some misinformed person did that, not the factory.

  12. Sho says:

    I saw the filter caps, and mine looked fine. Mine was made in 2004, cream board.

    They all had nothing comping out of the ends. I still replaced them with 450V xicon caps, and doubled the 47uF one with another in parallel.

  13. Bill: Will a 100mf 350V filter cap simply not be applicable? I noticed the current into the cap was 329V. I have one on hand and thought I’d use it unless you inform as otherwise. Thanks, JN

  14. That’s what I needed to hear! Perhaps “in stock” would’ve been a better choice of words. Thanks! JN

  15. James Via says:

    I’d recently put in new power tubes. Then treble, bass and middle pots needed to be re-soldered as they were knock loose when something heavy was placed on top of them during transport. When I plugged it in to play it worked briefly then crapped out.

    R 47 shows black burn underneath it on the board itself, also the caps ( C26 , C27 ) side facing the burned area of R 47 are also blackened but no leakage, and the R 48 shows a bit a burn on its surface but not blackened. Cap C 28 is clean. This is a cream board dated 2003.

    I was thinking of doing some of your mods while it’s all apart but I need to resolve this first.
    Any help/advice would be appreciated. Thank you.

    • bill says:

      The R47 burn is usually caused by a failed screen grid on V4 or V5, so you need a new set of output tubes. The 100 ohm screen resistors are supposed to go first, but in the real world they never do and the shorted screen takes out R47. The damage is mostly superficial, from the resistor smoke.

      Scrape the carbon off the board (it’s conductive) and maybe reinforce the crater under R47 with some epoxy and a little cloth. Higher resistance on the screens will decrease the current and the stress on them. I’d recommend 470 ohms (1W, flameproof) at a minimum and some designers go up to 1500 ohms.

      I have some tips on printed circuit board repair here:

  16. James Via says:

    I can’t figure this out. What is the correct resistor size for my cream board R47 replacement? You also recommended replacing the 100 ohm screen resistors with something higher what are their locations, the R# for these screens? Thank you.

    • bill says:

      R47 on the cream board is 2.2K. Make sure you have the right schematic; the PDF on Fender’s site has the green first, then the cream.

      The screens are R35 and R36.

  17. David McCoy says:

    Have a BJr and just went out after an hour of playing. There is output but its weak and there is a slight vibration or phase and almost a low octave that doubles with the note playing. Almost sounds like harmonizing notes when playing. Note there is one of the power tubes that has some blackness around it, but not sure if that is the issue. Can you help?

    • bill says:

      If the tubes aren’t fresh, you don’t have a solid, known starting point. But the problem could either be bad filter caps or phase inverter oscillation. See the appropriate links in the right column.

  18. MIke says:

    Hey Bill

    My Blues Jr, purchased in Sept 2005 (Cream board, so it is just out of warranty)last week began emitting a high pitched squeal, similar to an old radio tuner, that increased when I turned up the volume and/or engaged the FAT switch. It stopped when I removed the V1 pre-amp tube, so I replaced it with a new one, to no avail. So Googling, I came across your Bad filter cap thread, which prompted me to remove the back cover of the amp and inspect the caps, where I found one exhibiting signs of leakage. And if it IS that, how I can go about getting it to you for the repair ( I’m in Toronto, Canada), and some possible mods (standby switch, etc). Any info/help you can offer me will be greatly appreciated. Thanks.

    Mike Gordon

  19. Bryan says:

    Hi Bill. I purchased a Tweed B Jr in March. Re-tubed with JJ’s. Sounded great! Then last week while playing the amp began to produce a LOUD “honking” sound. My guitar signal was no longer audible. Frankly, it gave me quite a scare. I immediately turned it off and caught my breath. After about 3 minutes, I turned it back on and all seemed fine. The guitar sounded normal. Then, the honk came back like before. I tied to turn the volume down on the lead and master both with no effect to the honk. So I turned all the knobs including reverb. No effect to the honk.

    I took the back off to inspect the board. Nothing looks out of sorts. The caps are not leaking. The tubes are secure. No burn marks, etc.

    Any suggestions on what would cause this honk?

  20. kbell101 says:

    Hi guys

    I had added almost all of billm’s updates and the sound was some better, but still a bit thin and tinny, raspy when driven a bit. My caps did not show signs of leaking, but I decided to change them anyway. After the update, I got the bottom that I was looking for and the tinny sound is now gone.


  21. Hepcat says:

    Hi, Bill, I just repaired a BJr from 2003 that belongs to a student of mine. It was humming worse than usual and had strange sounds on low frequency notes. A scope look at the power supply found 50 volts of hum riding on the B+ line. The three 20mfd caps were leaking also, just like in your picture. I changed them all and it works well now. Doubled the big cap as you suggested and its a bit clearer. Also changed the bottom resistor in the divider providing the bias to a 27k and the bias voltage went up to -12.5 volts. I think the tubes are a little cooler now. Finally, the reverb tank return coil was open so I replaced it with a similar Accutronics that I happened to have around. It sounds better than the original did (if my memory is correct). The replacement had the numbers rubbed off but it measured about 200 ohms in and out. Other than these problems, it worked fine! LOL! Many of my students have Blues Juniors and they all like them very much. Nice amp but I’m a jazz and blues player. I started making amps recently and have one with the topology of a Deluxe. Used a Weber sig12B speaker and tuned the voltages/ and tone stack to my taste. Build the cabinet out of solid pine. A lot of work but great fun and very satisfying. Sorry about the length of the post. You do ask us to let you know if we have the filter cap problem.

  22. tosty says:


    I have a 1996 green board BJ. I was thinking about changing the caps and have noticed they are 22uF 500v instead of 450. Should I replace the caps with 500s or 450s? Would the extra voltage in the caps be causing any humming?

    • bill says:

      The voltage rating on the filter caps is the maximum voltage they can withstand. The maximum voltage in a Blues Junior is only around 330V. So the 450V caps found in current Blues Juniors provide plenty of safety margin. The 500V rating was unnecessary at the time and it’s unnecessary to replace them with 500V caps. The voltage rating has no effect on the filtering capability. The first place to look for hum is usually the tubes. See “Tracking Down Hum in a Blues Junior.”

  23. seymor says:

    my fender blues junior plays an octave down when on vol/master´s not an perfect octave;sounds awful.i´ve already replaced all tubes (all new) but the problem is still there…need your help! thanks

  24. seymor says:

    hey bill, thanx so very much for your reply!!! it´s a 2002/2003 cream board.

  25. Satchel says:

    Hi Bill,

    The R47 blew in my Blues Junior and I just want to know where I can buy the replacement resistor and how to clean carbon off the board. I know it’s been asked, but I’m a new owner and don’t wanna mess anything up as I’m not familiar with the layout! 😀 No other resistors or caps are blown just this one thankfully!
    Thanks for your help!

    • bill says:

      R47 burned because the screen grid in one of the EL84s failed. It drew too much current and toasted the resistor instead of popping the fuse.

      Scrape the carbon (burnt circuit board) with an X-Acto knife. Remove the smoke damage with an abrasive eraser or a bit of Bon Ami on a damp cloth.

      R47 is 2 watts, 2.2K metal oxide. I’d replace with a 3 watt to increase the chance that the resistor would survive and the fuse would blow in the future. It’s available here
      and from other electronics suppliers.

  26. seymor says:

    it was the output transformer causing all that´s been replaced & junior´s working fine….

  27. sluggo42 says:

    Hi BIll,
    Getting ready to install my basic mods. I ordered new caps along with the basic kit just cuz it’s an 03, and sure as punch, when I opened it up, all 3 were oozing goo. So, I’m glad I ordered them!

  28. osama says:

    hey Bill
    i have a problem a small thing from my motherboard dropped
    its named R47 does it mean that my pc i gone?

    • bill says:

      If it’s a cream board, the amp won’t operate without R47. It’s a 2.2K 2 watt resistor.

      On the green board, it’s part of the reverb circuit, a 470K 1/4 watt resistor.

  29. wksohn says:

    Hi Bill,

    I’ve been using two MIM FBJ. If I turn up the Bass knob, one amp gives me very open and loud Bass sound, but the other one gives me something different. If I turn the Bass knob more than 5, it starts to give me less Bass ( I know it may sound weird, … ) and a little bit fuzzy sound. It’s hard to say fuzzy, but anyway getting less clear. Definetely the sound with distortion or ovedrive is not good with more than 5 Bass knob. For the both amps, I cannot find the QA tag so I’m not sure when they made, but the one with the issue looks younger than the first one. (made in around 2003 maybe ??) Could you give me any thoughts or recommendation please? Thanks!

  30. Markus says:

    Hi Bill,

    I just got my BJ 2008 back from the tech, something else, but I noticed a hum ca. about 200Hz, I don’t know,
    but it was the same with the master down on 0.
    It is not loud, it also does not change with the volume, there comes just other noise, but with gain and guitar amps that should be normal. It is definitely no ground problem (just the amp alone).
    Do you think it is the caps?
    Is there a safe way to look?

    Greetings from Germany

  31. pwittbold says:


    I am planning to replace my filter caps in a 2003 blues junior. I was planning on getting Lelon 22uf and 47uf caps from this website.

    Are these the correct caps to use, and is there ay more “bad caps” on the market that I have been reading about. I am assuming lelon makes a good cap.


    • bill says:

      While you’re replacing them, you should increase the first filter cap to 100uF 450V. Bad caps were a chemistry problem ins 2003-2004. They’re no longer a problem.

  32. jgsinc says:

    Hi Bill,

    I just registered to your site tonight, and ordered a few of your mod kits for my BJr. I think the re-cap kit is going to solve my immediate problem, and I’m looking forward to the improvements that the basic kit and the audio taper pots will provide. I have a 2003 model and it has the the leaky cap issue. I discovered it while trying to track down a 120Hz noise issue. The noise is present with no input, regardless of settings. I pulled the pre-amp tubes one by one, and the problem persisted. Even with V3 removed. I suspect the the leaky filter caps in the power supply. Let me know if you agree. When I removed the output tubes, the noise decreased dramatically, but to my surprise, the amp wasn’t completely silent. Is the slight hum I am hearing being coupled from the input to the output transformer? Let me know what you think, and thanks for your help. I really appreciate the work you put into helping fellow tube amp enthusiasts.

    Regards, John

    • bill says:

      Yes, you’re hearing direct coupling from the power transformer to the output transformer. With fresh, balanced EL84s, most of that hum gets canceled in the output circuit. The metal hum shield on my site may help if you find that hum persists even with fresh tubes and filter caps.

  33. tobiemunroe says:

    Seems there is a crackle in my cream board blues jr. I took off the back and noticed if I lightly “wiggled” the 47uf cap it would crackle. Does this seem correct? without taking it apart, could it be bad solder connections on the other side? Thanks and looking forward to my mod kit I ordered this week!


  34. flmike says:

    Just picked up a 3rd hand 2003 Blues Jr. last week, love the amp, but I am experiencing intermittent buzzing, thought it was my Cry-Baby pedal, so I took it out of the loo and still buzzed, then I took by DS-1 out of the loop and yup, still buzzed, then I had the bright idea to move the wall-wart for the pedals to a different wall outlet and moved the power line away from the amp, this helped a lot, but there is still a buzzing. I also noticed that when I tried to slide the amp (not across the room, just re-angled it) on the tile floor I got a real bad crackle and pop (maybe loose valve sockets?), and the input jack is very loose, not in the mounting, but the internals. I plan on opening the patient this evening and doing a full inspection, something I have been avoiding since I’ve only had her a week and really haven’t stopped playing since I picked her up. I’m pretty handy with a soldering iron (one of the perks of being a retired AGE troop, the USAF loves to teach you how to solder) and a multimeter. After tonight I’ll have a better idea if anything else is up with her, but, from what I’ve described, what mods/fixes/upgrades do you recommend for an out of the box BJII?

  35. LousyViking says:


    About 2 months ago I noticed a sudden and pronounced “mushiness” in the low end of my (Billm modded) Blues Jr. and also what I would describe as an intermittent ugly distortion (crackly or gravelly sound) at volume, even on the cleanest setting. When I opened the back of the amp, one thing I noticed was a discharge (similar in look to foam insulation and not entirely unlike the picture above) at the bottom of the center (C18 position on the circuit board) filter cap. I took the amp to a TSI, explained the symptoms and explained what I saw on the filter cap. Well, $125 later, they did some other repairs, but did not replace the caps as I asked. The mushiness appears to have been solved, but crackle (especially after the amp has warmed up and I am playing chords vigorously) remains. Does my symptom sound like a failing filter cap and is it self evident that I need to replace them? Also, is it just the three small caps that I need to replace? I don’t know the exact year of the amp, but it is a green circuit board.

  36. Just got gifted a cream board Blues Jr. that “doesn’t work right”. Has a serious hum issue of about 125hz and a lot of strange artifacts and harmonics on the notes sent to it via my guitar. V4 isn’t lighting / heating up. The hum goes away when I remove V4 but alas, no sound at all either. Also checked the 22uf caps and they look just like the ones in the picture. I’ll replace the caps, should I also replace the socket on V4?

    • bill says:

      You might just need to resolder the joints on the socket and re-tension the socket springs so they make better contact with the tube… and I assume the tube is good? It could be defective, shorted internally.

      The amp will sound terrible on only one output tube, so get that working first, along with the new filter caps.

      While you have it open, I’d suggest testing it to make sure it’s working more or less correctly, then doing the basic mods kit to improve it. In the stock amp, V4 can run hot enough to destroy itself because of phase inverter oscillation. The 100pF cap included in the basic mods kit fixes that.

  37. drburns says:

    Hey bill, I’ve replaced my 22uf caps about a month ago, now my 47uf has gone bad, can I order just that one alone, or do I have to get the whole kit?

  38. Larry Cramer says:

    Hi Bill,
    I have a MIM Cream board Blues Jr. It developed a problem where now when I engage the Fat switch it emits a high pitched sequel. After reading your Tubes page I put in all new JJ tubes in hopes that would cure the problem. It did not. Do you know what the most likely cause of this is. I live in a small town where Amp techs are non existent. I’d like to at least be able to point the techs here in the right direction. Thank you so much for your help and all you do.

  39. bluewater says:

    Just completed the Cream Board “Basic” and “TO20” transformer mods. The installation and resulting tone was entirely satisfying! Thanks!!!
    No problems seen with the 22uF caps. My 47uF cap was showing signs of leakage, but the 100uF replacement did the trick to clean up the hum.
    Dave AKA Bluewater

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