This one belongs to a really fine jazz player I know. He uses it for solo gigs. Yes, it can happen. A 5 watt tube amp for jazz! A little breakup and warmth makes music sexy. An Ibanez Ts-9 with a Roland Jazz Chorus? Um, not sexy.
So what was the trouble? The amp would work for about 20 minutes then crackle out and die. He would plug into the other input and it would die after a few more minutes. The client was frustrated as this is his favorite amp and it's been to another tech who couldn't find the problem. Truth be told, I couldn't either till tonight and it took me a week. Oh, I did everything: the ol' chopstick test, tested the caps, resistors, cleaned and tightened everything, checked the sockets. I even changed the cathode caps only because on the 6V6 tube there is 23 volts sitting on a 25 volt cap. I don't like that. I prefer a 50 volt or better cap there. I've seen those lil' Sprague Atoms pop like a firecracker.
I saw this baby was loaded with a JJ 12AX7 and 6V6. Their preamp tubes in my experience have all sorts of reliability issues. So I put that tube in my tester and let it cook overnight just to see if the heat caused any shorts. Nope. Not even tapping on it caused any trouble. This one was made on a good day.
So I could not get this amp to not behave like a champ! (Yes, stupid pun intended!). I did find one disconnected ground wire flopping about which could reach the input wire by the 12ax7 tube. This wire once was connected to the pin 9. The heaters were improved in this amp, lifting that side from ground and 2 100 ohm hum balance resistors were installed. Well done but why leave that wire?
This brings me to my point. I spent a lot of time I can't justify billing for on this amp due to another techs sloppiness. I replaced the cheap signal caps and the ones what were in there were barely soldered. So I figured maybe this was the problem. But once I soldered the new caps in it finally quit on me! YES!!!! If it ain't broke I can't fix it. Now I had something to fix! I hate turning a project in that I don't feel 100% right about.
Yup. A washer. Flopping about like that drunk and annoying hobo asking for a sandwich. Right under the solder joint where the first .022 cap and wire connect. When the amp was taken apart it must have come loose and gotten lost in there.
And here is is back in it's proper place:
Man this kind of thing....well, yeah, job done.
This is a great little amp. The power transformer was replaced some time ago with an early 70's part so the B+ voltage is a bit higher which I like. Also the speaker is replaced with a Kendrick. I don't really dig his speakers but in this amp it's a great choice. I installed a NOS GE 5751 tube so it has a nice darker and warmer voice to it. This is a terrific amp. Sad to see it go home tomorrow but happy to get paid and have another satisfied customer!