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I'm into a mid 1990's tube guitar amp that failed a 6CA7 output by developing a carbon path between the plate pin and heater pin. Tube tested short, and found the burn marks on the tube socket and later tube when I went to replace. So, tube sockets on the way and a pair of Mullard outputs in hand. Now, my question - this uses "modern" electrolytics in the power supply. They are more than 20 years old. No signs of overheating. Should those be replaced as a preventive or left as long as things look and work ok? I dont want a repeat.
If I could find the place called "Somewhere", I could find "Anything" 
Tim
Jesus cried out and said, "Whoever believes in me , believes not in me but in him who sent me" John 12:44
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If it has worked recently and you have seen no degradation (hum, clipping) - you could leave them be.
You could possibly unsolder few wires and check the capacitance to make sure it is OK.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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Kinda thinking the same. Its not something that is going to get a lot of use. Here's a couple pics of things.
If I could find the place called "Somewhere", I could find "Anything"
Tim
Jesus cried out and said, "Whoever believes in me , believes not in me but in him who sent me" John 12:44
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Condensers are not that expensive. Were it I, I would replace the filter condensers as a preventative measure, if they will fit, with ones of a higher voltage rating.
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I can't see what brand those are, but if they are from a quality manufacturer I would consider leaving them, otherwise I'd replace them with a known quality brand from a vendor like Mouser. A.E.S. carries Solen 630V Metalized Polypropylene that I often like to use in place of electrolytic caps but they don't seem to carry radial leads or values above 47 uf.
https://www.tubesandmore.com/products/ca...nd%3DSolen
John KK4ZLF
Lexington, KY
"illegitimis non carborundum"
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+1 what John (Eliot) said.
If they are Nichicon or Panasonic, or possibly United Chemicon and there is no hum, then you might chance leaving them. Any other brand, then replace - with Nichicon, Panasonic or United Chemicon (in that order with Nichicon being the preferred brand). Relatively cheap insurance. 
--
Ron Ramirez
Ferdinand IN
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Samwha caps. Sounds Japan to me.
If I could find the place called "Somewhere", I could find "Anything"
Tim
Jesus cried out and said, "Whoever believes in me , believes not in me but in him who sent me" John 12:44
Posts: 13,776
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Samwho?
Never heard of that brand. Replace...Nichicon is your friend. Or Panasonic.
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Ron Ramirez
Ferdinand IN
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I am not sure Chinese caps were popular (or even existed) in the beginning of 90s on American market.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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I finally had a chance to update. I replaced all the power HV supply caps with the good Nichicon brand from Mouser. I didnt replace any of the lower voltage caps, but I may need to. I put new ceramic tube sockets in, which was fun since they were soldered between the PC board and bottom of the tube socket instead of opposite sides. I installed a new pair of matched Mullard output tubes and bias looks about right (-33V if I recall). Im not sure just how well they are matched tho. There is a slight difference in cathode current when I monitor, but is small. They both draw slightly either side of 50ma at idle. I cleaned all the controls and fixed the speaker terminal connector after it broke off when disconnecting. I have a couple minor issues, which one I believe is the 12AX7A preamp tubes. I have some static, hissing or whatever when I first power up, but diminishes once it warms up for a few minutes. I plugged a new short plate JJ tube (only had 1) in and it helped quite a bit, but still had some noise. It is very quiet with the 1st preamp tube pulled and the JJ tube in the 2nd tube/splitter. It is noiser with the original tube, so I have a new set of Tung Sol tubes coming. Ill see if this silences it.
The next is a low level 60/120 cycle hum that is dependent on the tone controls. Its almost not noticeable with the tone controls zero'd. So, I will probably go after the e caps in that section and on the DC line of the filaments.
If I could find the place called "Somewhere", I could find "Anything"
Tim
Jesus cried out and said, "Whoever believes in me , believes not in me but in him who sent me" John 12:44
Posts: 15,825
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My guitar teacher owns several Trainwreck amps.
He knew Ken Fisher well and those were gifted to him.
Nowadays those are worth a fortune.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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To me, this is one of the best sounding amps I've heard! I really like the fact you can set it for an acoustic or use a bass guitar. Most amps I've seen are one or the other. I put the new pre tubes in and it silenced the noise, so down to tracking down a hum in the preamp section. It's not bad, and would pass like it is, but if I can diminish it, that would be great. Got a couple low voltage e caps on the supply line for a couple mosfets on the cathode of the 12AX7a's. May be the culprit. I'm posting a PDF schematic.
If I could find the place called "Somewhere", I could find "Anything"
Tim
Jesus cried out and said, "Whoever believes in me , believes not in me but in him who sent me" John 12:44
Posts: 1,130
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Joined: Jan 2014
City: Annapolis, IL
I pronounce it fixed. I replaced the rest of the e caps, put back together and found some of the cracking static came back until it warmed up. I pulled both boards and resoldered a bunch of suspicious looking connections. I put back together kinda loose to be able to flex things and pull again and had no sound at all! Huh ... so after some messing around I found flexing the board made the sound (and static) come and go and could see the output tubes flash inside (not sparking, you know -the look inside when the tubes are handling current). Well, I discovered the outputs were grounded through the screws and stand-offs that hold the octal tube sockets to the metal chassis! So, I went back and cleaned and tightened those screws very tight - quiet as a church mouse! So, if anyone has one of these amps with static/cracking noises and cleaning controls and replacing tubes doesnt completely quiet it, clean those studs or solder a ground to those to chassis ground. I still have a very light, low level hum, but I think it is the nature of the beast for the most part. It's not really HiFi, so it may not be completely quiet like a Fisher or Dyna.
If I could find the place called "Somewhere", I could find "Anything"
Tim
Jesus cried out and said, "Whoever believes in me , believes not in me but in him who sent me" John 12:44
Posts: 13,776
Threads: 580
Joined: Sep 2005
City: Ferdinand
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JJ might be OK for preamp tubes, but when it comes to audio output tubes - avoid JJ.
--
Ron Ramirez
Ferdinand IN
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