Bad Filter Caps in New BJrs
I’ve got yet another Blues Junior on the bench with bad filter caps. In this one, all three of the 22μF 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 (which I use), Nichicon, or F&T.
HI! I had this problem. I repair and replace first condensator on 100mkf [100µF].
Photo: http://forum.harmonica.ru/viewtopic.php?f=19&t=126166
p.s. Sorry for my english.
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.
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!
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.
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!
Dan
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.
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.
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.
All of the “-con” caps are pretty good. Nichicon, Xicon…. Just make sure they’re 450V.
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.
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?
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.
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.
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.
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?
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.
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.
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.
my filter caps went out what do you recommend? Are they included in your cream board basic kit?
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.
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
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.
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.
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
Why screw around with the wrong caps when 450 volt caps are readily available? “On hand” is a false economy!
That’s what I needed to hear! Perhaps “in stock” would’ve been a better choice of words. Thanks! JN
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.
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:
http://billmaudio.com/wp/?page_id=204
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.
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.
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?
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.