Please please help svt classic problem

[Dave516]

Hello there, currently I am having an ongoing battle with my SVT Classic (199?). The issue I am having currently is when the amp goes from standby to on I get a nasty crackling noise. After a minute it goes away and then comes back 10 minutes later then leaves again and so on. All 6 (6550) have been replaced a couple months ago, as well as all 5 pre-amp tubes (3 12ax, 2 12au). I have had the amp apart and the solder joints looked fine. I can also reproduce the issue with a chopstick when it is acting up. I seemed to have isolated the issue to the back preamp section; if I tap anywhere around there when the amp is freaking out it goes ballistic. So today I once again swapped all three back preamp tubes (2 12au, 1 12ax). Still I have the same issue I read something about a noisy load plate I don?t know what that is or how to test it please help me. I haven?t been able to play out with my head in weeks for fear of it acting up live.

[Enzo]

The preamp is the part where the front panel controls are. The large chassis in the bottom is the power amp. The three small tubes in the bottom area are the phase splitter and driver tubes, which are part of the power amp.

LOOKING OK is not the same thing as BEING OK when it comes to solder. REheat and reflow any solder connection that seeems possibly involved.

Tapping that causes the symptom tells you that there is a loose connection. SOlderwork is always suspect, tube sockets get loose or corroded, parts get cracked and/or thermally sensitive. ANy place there is a ribbon cable connector is suspect. REsolder the makes and a little cleaner up the females.

ANd welcome to the forum. It is not necessary to post the same issue in several places.

[Amp Kat]

The last one I had that did this was a bad standby switch. It is possible that something is loose as that amp has serious vibration issues afetr all 6-6550 's on top of a cab would rattle anything. I know one guy locally that doesn't put his head on top of his cab and he has reduced his repair bill by 10 fold.