Marshall JCM 800 reverb noise

[Randall]

I've got a 1990 JCM 800 model 2210 that makes quite a buzz with the reverb on full and all other controls at zero. The reverb ois working, it's just buzzy. Footswitch will kill it, pulling V3 doesn't effect it, but pulling V4 does stop the buzz. Different tank, same thing. Grounding the V4b grid actually makes it worse.

I think it is less after hitting the connections on V4, but I am not 100% on that. I know it seems kind of odd to turn the reverb on a Marshall up fully and worry about some buzz, but the guy runs it with a full stack and says it is in his face.

Any ideas?

http://www.ampwares.com/schematics/m..._100w_2210.pdf

[nosaj]

I've got a 1990 JCM 800 model 2210 that makes quite a buzz with the reverb on full and all other controls at zero. The reverb ois working, it's just buzzy. Footswitch will kill it, pulling V3 doesn't effect it, but pulling V4 does stop the buzz. Different tank, same thing. Grounding the V4b grid actually makes it worse.

I think it is less after hitting the connections on V4, but I am not 100% on that. I know it seems kind of odd to turn the reverb on a Marshall up fully and worry about some buzz, but the guy runs it with a full stack and says it is in his face.

Ay ideas?

http://www.ampwares.com/schematics/m..._100w_2210.pdf

Check for DC going into reverb tank?

nosaj

[Randall]

"Check for DC going into reverb tank?"

No, it's clean on the cable plug.

[nosaj]

"Check for DC going into reverb tank?"

No, it's clean on the cable plug.

What about c29 or c26? Scoping the signal will help the process.
nosaj

[g1]

How is it with the reverb on 8 ?
Just because he wants to run it at 10 doesn't mean it didn't buzz like that when new. I would expect buzz and you need to know whether you are dealing with a fault or being asked to re-design. With no master and reverb set to 10, there will be buzz, just a question of how much is normal.

[Helmholtz]

Does the buzz stop if you lift the collector lead of TR2 or one end of C48?

[Chuck H]

I've had several buzzy tubes new out of the box. Did you try another tube in the V4 position?

Also, might try bypassing the V4B cathode. If there's too much gain you can always increase R42 to achieve unity.

It's probable neither of these are the solution, but possibly and they're easy to try.

[Randall]

I did try other tubes, but I decided

1. It's really not that much buzz, and I may have corrected some of it by soldering the socket. It's a full 100 watt Marshall stack, how much can some reverb buzz matter?

2. I really don't want to flip this board to try much else for something that may not even really be a problem. I can live with cutting my losses and referring him to the nearest Marshall shop 100 miles away at no charge. I'm getting old and becoming more and more selective, I don't need to accept every single problem that walks in my door.

Thanks for trying to help as always.

[Chuck H]

I'm getting old and becoming more and more selective, I don't need to accept every single problem that walks in my door.

True. But then you miss being their guy when they have easy stuff or any referrals. Still, it's probably not an actual circuit failure and you're not the type that wants to redesign every 'meh' circuit that comes through your door. On that note, when I started contracting a smart man told me that a good deal of my success would be determined by the jobs I don't take.

[John G]

Randall,
Sorry for the late reply, Your problem rang a bell, so I dug out my Marshall schemos like your 2210 and found s note to self that went.
"Check ground point at reverb transformer.........................add an additional wire soldered from the ground leg of R39 to the grounding point on the existing transformer frame to reduce hum.
So that's it, a bit vague but then it was 20 something years ago and don't remember the fine detail.
It may help it may not.
Cheers
John
that

[Philr228]

Hi,

Probably a bit late now, as just revisiting this site and read this thread.

I too had a problem like this on my old Marshall 4210 and after a lot of testing and resoldering, changing valves/tubes etc. what sorted it out was making and remaking the connections to the reverb tank several times. I talking about the phono connections here!

Give it a try, might do it!

Cheers

Phil