Jet City BUZZ...

[leadfootdriver]

I got the amp at a blowout price, so I'm good with that. I dig the tone for the price, but this amp has a rippin' BUZZ to it! Turning up the master, even without a cable plugged in yields the buzzzzz... I'm sure it was a corner cut to meet a price point.

Anyone have a remedy?

[loudthud]

It would help to have an exact model name or number and a link to a schematic if you can find one.

[Chuck H]

I'd start with a preamp tube substitution and take notes on the tube pull/noise results so I'd have a place to start if it isn't a bad tube.

[soundguruman]

There are some schematics posted here:
http://music-electronics-forum.com/t34709/

[leadfootdriver]

THanks guys. It's a JCA5012C. I suppose it's the same as a JCA50.

[Chuck H]

I doubt it's buzzing because the manufacturer cut corners. It's broken more likely. The problem description of "rippin' BUZZ" doesn't get us to a solution. Have you tried pulling tubes? Starting with the first preamp tube, buzz still there pull the second, etc. If you find a tube that stops the buzz when pulled try replacing it with a known quiet tube (that doesn't mean a new tube that hasn't been heard). If the buzz remains we move to the next step of troubleshooting what may cause the buzz in the circuit you isolated when pulling tubes. OR...

Take it to a repair shop.

[leadfootdriver]

I pulled the Chinese wb's and replaced them with Chinese WA's but they might be rejects for all I know. I haven't swamped the power tubes but it plays at full power. Its just buzzy like having single coils near a flouresent light.

[Chuck H]

That's still no information. I mentioned before:

Have you tried pulling tubes? Starting with the first preamp tube, buzz still there pull the second, etc.

This was to be done as part of tube substitution and would have given us a place to start.

[leadfootdriver]

I should have clarified that I put the tubes in way before this thread. Even so, I swapped in a set of JJ's and the buzz is the same.

It's pretty much AC ripple. According to the schematic, there's plenty of filtering. But, are all 1N4007 diodes created equal?

[Gingertube]

Watch that posted schematic, sheet 1 has had the BF applied to it to confuse people. pin 1 anode belongs on the other triode section, ditto pin 6 anode. The anodes have NOT been numbered incorrectly, they (the tube symbols) have been drawn incorrectly, look at V4, that clearly shows that the anodes are drawn on the wrong triode sections.
On sheet 2 however V5 has been drawn correctly.

Cheers,
Ian

[leadfootdriver]

YEah, I don't think it's a JCA schematic. It's just what I can find on the web.

Thanks!

[Chuck H]

I should have clarified that I put the tubes in way before this thread. Even so, I swapped in a set of JJ's and the buzz is the same.

Have you isolated the buzz by doing a tube pull? (broken record broken record broken record broken record broken record broken record broken record broken record broken record broken record broken record broken record broken record broken record broken record broken record)

It's pretty much AC ripple. According to the schematic, there's plenty of filtering. But, are all 1N4007 diodes created equal?

No. But it's still unlikely to be the problem. Why are you looking past standard troubleshooting techniques and targeting the specifics of different 1N4007 diodes!?!

It's probably a bad ground or decoupling circuit. Maybe a bad relay or coupling from the relay power supply. We have no way to find it if you're just going to float around the advice you asked for.