Ampeg V4 60 Cycle Hum - Pronounced When Reverb is Turned Up

[Stovemananon]

Hello all,

Hope you are doing well!

I was wondering if there are any Ampeg Enthusiasts out there who might help me out. I have a V4 VT-22. It sounds great and everything works fine. I just put in new capacitors and a three prong cord. However, when I max out the reverb, I get a 60 cycle hum. The hum balance pot does not help. When I disengage the reverb circuit with a foot switch or turn the reverb down, the 60 cycle hum goes away. It sounds as if the power transformer hum is being amplified.. which I guess is what a 60 cycle hum is anyway.

Anyhow, any ideas on this?

Thank you in advance!

[dorrisant]

Pictures would help... that said, how is the reverb tank positioned in relation to the PT?

Can you move it around while it is humming at the amps worst settings and see if the hum varies with a different orientation. Other than that, how are the wires associated with the reverb run inside the amp? Could there be a proximity issue there?

[mojotom]

May be check your hum balance pot, I had issue with noise and buzz on mine, send it to a tech but they didn’t find the issue. I then change the hum pot and hum was gone.
If a tube go bad it can bring down that hum pot. And reverb become almost unusable due to hum.

At least something to check on those Ampeg.

[Stevem]

The side of the reverb pan labeled output can not be on the same side of the amp as the power transformer.

It may be that the pan was remove once to check it, repair it or replaced it and it was reinstalled wrong on the lid of the amp.

Also confirm that the sheild of the cable on the output side of the pan is at chassis ground and the whole pan itself is at chassis ground.

If a incorrect replacement pan was put in then this may not be the case.

[Stovemananon]

Thanks for the replies and great advice.

I appreciate it. I'll check the hum balance pot. I will also check the output cable to chassis ground!

I took the reverb tank out and the hum/buzz persists exactly the same without the tank connected at all.

I guess this means ruling out the reverb tank, right?

[Stevem]

Well what you need to do to fully prove that is to place a short across that cable that feeds the output side of the tank.
If with that done and the reverb turned up max if you still get hum, then yes something else is going on.

[Stevem]

V203 ( 12AX7 ) the reverb recovery stage could be bad / shorted and produce that hum.
Yank that tube out, does the hum stop?

[bepone]

i had 2 pcs of V4. one /totaly burned and previously converted to EL34's) i have dissasembled until the last wire and do all from the 0. very nice amps. construction is on advanced level.
hum can be from oxide on the connectors, not connecting the ground properly, easy to clean that first and see.

[Stovemananon]

Well what you need to do to fully prove that is to place a short across that cable that feeds the output side of the tank.
If with that done and the reverb turned up max if you still get hum, then yes something else is going on.

Thank you.

Do I short it to ground? If so I have done this and the buzz disappears.

[Stovemananon]

V203 ( 12AX7 ) the reverb recovery stage could be bad / shorted and produce that hum.
Yank that tube out, does the hum stop?

THE HUM DOES STOP!! I put in a good tube just to see if it was the tube, and the hum came back. What else could it be in this stage?

ALSO, THANK YOU FOR THE FIRST LEAD I'VE HAD IN HOURS!

[Stovemananon]

Regarding V203, I have replaced the following surrounding this circuit.

c210 .005 uf
c211 10uf at 25v
c212 .005 uf

replaced components.png

[bepone]

the oxide on the reverb tank connectors? or cable broken inside the tank? or grounding wire on the reverb tank inside?
when connected all , power off, test with the multimeter ground continuity from amp chassis to reverb tank chassis=?

[Stevem]

Check the integrity of that output cable, does the sheild connection at the board have contenuity to the rca end?

If that test good then place a short right across that rca end, when doing that does the hum stop?

[Stovemananon]

the oxide on the reverb tank connectors? or cable broken inside the tank? or grounding wire on the reverb tank inside?
when connected all , power off, test with the multimeter ground continuity from amp chassis to reverb tank chassis=?

Thanks for the response!

It appears that even with the tank removed the buzz persists.

[Stovemananon]

Check the integrity of that output cable, does the sheild connection at the board have contenuity to the rca end?

If that test good then place a short right across that rca end, when doing that does the hum stop?

Thanks for the advice!

When you say “shorting” do you mean to short the rca end to the ground sleeve?