Ampeg 3Pro. Sound cutting out/crackling.

[Goingdownslow]

I have a fault on my SVT 3pro that is similar to what you would get with dirty in/out sockets. I have cleaned the contacts on the sockets thoroughly, even tried linking them with a patch lead but to no avail. I know it is on the power amp section as I have tried different pre/power amp permutations. It does not always do it and it seems to do it more on low volume. A quick flick of the volume control up and down cures it for a while. It is not the bias.
There is one more set of contacts, and I have had a problem with this on a hifi amp which was cured by cleaning, and that is the speaker relay.
Has anyone had this problem with a speaker relay?
It looks a bit fiddly to get at and pop the cover off but I will attempt it If I can't locate the problem elsewhere.

 

[agedhorse]

What about some proper troubleshooting rather than guessing?

A scope, generator and a good bit of knowledge will sort this out very quickly.

Fixing parts that aren't broken often break they, causing new problems.

If a jumper around a loop doesn't resolve the issue, it's not the switching contacts inside the jacks, so cleaning them won't help (as you have discovered).

What is your knowledge level, do you understand how global NFB amps are supposed to work? Do you have a scope, signal generator, multimeter and know how to use them SAFELY?

 

[JimmyM]

^^^ What he said. However, one other thing you can try is swapping out a known good tube with the others one at a time. Or you could just pull them and reinsert them to see if there's a dirty contact around the pins. A bad tube can cause crackling, too. And if that doesn't work, refer back to Andy's post and take it to a shop. You'll save $ in the long term.

 

[agedhorse]

It is possible that it's either V1 or V2 on the power amp.

 

[Goingdownslow]

Just an update.
The amp has been performing well since cleaning the contacts on the speaker relay.