AC30 HWH - Volume dips/fluctuations

prlgmnr

Any ideas what might cause this?

It's most noticeable using gain pedals as there is a big sudden drop off of volume/gain or sudden increase, but I've also been able to reproduce it just going straight in, both with the master volume bypassed and the channel volume on low or with the master wound right down and the channel opened fully up. Seems to happen on all channels/inputs regardless of settings (not that it's an amp laden down with knobs and toggles).

My best guesses are:

1. Time for a retube (have had the amp for about 8 months and haven't used it heavily at all but no idea what the previous owner/s have done in terms of revalving). 
2. This particular amp doesn't like dodgy farm outbuilding power and I need some sort of voltage regulator (I've just got one of those thingies with a coil in it that's supposed to limit interference at the moment but I'm not sure how much they really do). 

Any other possibilities? And any recommended techs in the Yorkshire area? I've heard good things about Mac Amps in Leeds.

ecc83

If it is just the VOLUME of sound that is changing and not the level of distortion that is going to be in the pre amp section I would think maybe up and inc' to the PI?  Swap the PI for another valve and tell us the result.

Could be a valve or a bad solder joint. If the drop in volume stays for a time try the highly technical "hand acceleration test" i.e. thump it. If that has an effect, likely a joint. But I am not  a Vox expert and there could be something known?

Power wandering up and down will not usually bother a valve amp except absolute clipped output power. There is nothing remotely cheap that I know of that can regulate 100s of watts of mains power. You can get "continuous conversion" UPS units but they ain't cheap. If it really is a problem your best option is probably a small 1/2 horse generator?  But I shall have a look....

Dave.

ICBM

A change in *gain* (which will also affect volume) is most likely early in the amp - preamp valve, or bad solder connection - whereas a change in *volume* (not affecting gain) is most likely late in the amp, and could even be the speaker connections. A change in both can also be caused by power supply voltage drop.

Dodgy outbuilding power is not a good idea, either for the amp or for your safety. It's perfectly possible for it not to be dodgy if it's a proper cable run from the main house, and if that's a likely cause then sorting that out is the first thing I would do.

prlgmnr

I'll give the old kinetic reset a try.