Crackling problem in 5E8A

[Bluefinger]

Hi,

I have discussed this in another forum and the amp has been checked by a tech but the following problem is still there so I need some fresh brains. Here'S the deal:

I have a self built 5E8A that worked fine from the beginning. Then after a couple of weeks it startet to crackle a bit and it got worse. It sounds a bit like bacon frying. It appears when the amp is idling and gets less when I play a guitar through the amp. When I stop playing, the crackling slowly comes back.
I have already replaced all resistors and caps and disconnected the whole tone stack. All solder joints have been redone and checked. Any ideas? Can these symptoms be caused by a faulty tranny?

thx!

[Enzo]

Not most likely.

Isolate the problem. Do any of the controls affect the sound of the noise? If so, the noise source is before those controls.

Pull the first preamp tube. Noise stop?

Go through the amp and ground grids where possible to determine which stages are carrying the noise.

[Bluefinger]

I checked that but ...

... here's what seems strange to me:

Crackling is very loud and gets more when the amp idles.
the tone controls do affect the sound of the crackle.
The volume controls affect the volume of the crackle but with the volume turned off, the crackle is not completely gone.
pulling V1 & V2 (each channel has a whole 12AX7 in this circuit) doesn'T have any effect on the crackle.
When V3 is pulle the crackle is ALMOST gone. it sounds very muffled and can hardly be heard but it is there. Removing the whole V3 socket doesn't change anything. The low crackling is still there.
The feedback resistor between the two gain stages was removed when the tests were performed.
When V4 (PI) is pulled, it's dead quiet.

So if most of the crackle is created before V3 but some of it is also created after V3, what can cause this? My only explaination is that it's coming from the power supply ... I can't find any other component that would have an effect on both parts of the circuit. If all caps and resistors have already been replaced, What except for the PT and chocke might be the cause?

Maybe I am missing something but this is driving me nuts and I can't find it. So many folks at the FDP have been a great help but yet, the amp is still crackling. I will get another amp kit with matching transformers in a couple of weeks but I wonder if there is a way to rule out the trannies and choke before that. It's such a great amp but I can't use it ....

thanks ...

[Enzo]

SO set your scope to about 1v/div, set it for AC coupling, and monitor the B+ in the sections where V3 is. See if the noise shows up on the B+. But the controls affect it, so I'd look befoer the controls. Tha fact that a litle leaks through means either the controls themselves do not go all the way to actual zero - quite common - or that whatever is making the noise is getting a little into the powr supply as well as coming through the signal path. Doesn't have to be either/or.

If it were a tranny or choke, it would make all this noise with V4 pulled. The amp is quiet that way though, so those parts are fine.

[Bluefinger]

Hmmm ... unfortunately I don't have a scope. Is there a "poor man's way" of checking this?
At least the good news is that if it's not the trannies that it's probably a cheap fix ... in case I ever find it )