Valve amp start-up worries.

WAD6550 Power amp. Power on as usual, as the amp starts to warm up, I get a sort of surging 'wom' noise that seems to originate from the transformers, then dissipates. It's quite loud and replicable but has never done it until today. This is all I need after the ongoing farago with my Tannoys. Any guesses as to what is on the way out?

Please say something easy to fix - I didn't build the kit and don't fancy electrocuting myself....

John

 

Could just be the mains transformer or the choke (located beneath the top plate) working loose. Check the bolts before doing anything else.

A loud BOING is usual at switch on.

 

A loud BOING is what I'm used to!

 

Interestingly, it didn't do it from cold this morning - although the low level mains hum through the speakers is starting to annoy me a bit . This suggests that something in the startup circuit is getting too hot and drifting out of spec, rather than a mechanical problem. The amp was being stopped and started whilst hot when I was getting the noise last night - swapping speakers around, since I'm STILL convinced one of them isn't quite right - irrespective of how many times I've measured the impedence and switched the crossovers. Secondhand speakers. Never again. Now, if only Tannoy would start selling 15" Golds again...