Dual Showman low freq oscillation

[capomonster]

Hi,
I received just some hours ago a Dual Showman I bought off ebay. The amp was sold as recently refurbished by TAD, which probabily is: Sprague caps and TAD brand inside, new power tubes etc.

I took it off the box, connected it, and "vibrato" channel worked ok, while the "normal" made no sound. I tried to lightly poke the preamp tubes, and they seemed to be quite loose in the socket. I tried to push them in firmly, played some more notes and one of them must have moved because a loud rumbling noise was produced.

So I took the head out of the cab, checked if the wires attached to the sockets were ok - and they were - the tightened the sockets' pin holders a bit with a tiny screwdriver. Put the amp back in, plugged the tubes in the sockets, and now as soon as I release the standby switch, a loud WOOOOO noise comes out of the amp. Poking the tubes changes nothing. The power tubes light up normally, and I swapped all preamp tubes with no extent.
any suggestion?

regards,
Maurizio

[capomonster]

I tried to switch the amp on with no v1 nor v2 in. something happened first, then I put v2 back in, the noise came again. but, i was not so quick to switch it off, so the noise slowly increased the disappeared. amp off, then on, no noise. both valves back in, no noise. strummed a bit... the noise seems to be gone!

can I trust the amp now? maybe it was some cap that needed recharging?
(sorry for the bad tech language)
regards,
Maurizio