Help.  Have had my amp for about three weeks and it has died on me. This is what happened. I have just purchased a Mr Springy reverb unit and was trying it out, first, in line, guitar - springy - amp, working fine. Turned everything down and disconnected the reverb unit, plugged guitar straight into amp, working ok, connected reverb through the effects loop, there was a very slight connecting noise/click/pop, not loud then nothing from guitar, it was like I had an open circuit in the guitar lead. With the amp on standby there is no noise from the speaker, switching the standby on has a small amount of hiss/crackle coming from the speaker. Tapping the centre pin of the guitar lead onto the chassis gives a sound out of the speaker. I did have the reverb unit working through the effects loop, I was trying to compare the sound with the revrb in both positions. ( didnt seem to make much difference, when it was working)  Any ideas? TIA

Hi Nick, thanks for your advice, I checked the power amp by running a signal in and it worked fine. I had printed off a copy of the amp design so decided to try and work my way through it with an ohm meter. I have not done this before with an amp but new a little about circuits from my days as a auto electrician, not really close but enough to give me some confidence in tracking through the circuits. quite fascinating. Anyway, couldnt find anything obviously wrong. So, plugged my guitar in, switched on and turned it up a little, nothing, then decided to turn it up a lot. I could hear a faint sound coming out of the speaker. Not enough gain perhaps so decided to check/change the preamp tubes. I replaced v1 and yep, its fixed. Must have been a coincidence plugging the reverb into the loop at the same time as the tube gave out. I havent tried the reverb in the loop again yet so will try that tomorrow. Cheers  AJ