Rivera Quiana Studio combo volume drop.

bdc64

Can anyone help me figure out why my amp is fine for 30/40 mins then the volume drops very low, I then turn it off for a while and it's ok for another while. The amp was serviced so all the valves are ok .

ICBM

bdc64 said:

Can anyone help me figure out why my amp is fine for 30/40 mins then the volume drops very low, I then turn it off for a while and it's ok for another while. The amp was serviced so all the valves are ok .

Not necessarily, especially if some of them are new. If it is one, it will be a preamp valve.

It could also be something completely different, most likely a resistor or a solder joint which is failing when hot.

bdc64

I am thinking it's a solder as the problem starts when the amp is warmed up. The tech could not find any fault when he had it running for an hour but once I had it back the problem returned.
I also tried 5 fully working preamp valves from another amp, same problem.

ICBM

Did he run it on the bench with the chassis open? If so that will have stopped it getting as hot. He will need to cover it with something like a sheet of plywood to replicate the condition.

These faults can be a bugger to find, but it does sound like it’s easier than something completely intermittent. Once it has cut out, it should be easy - as long as it stays like that for long enough!

bdc64

That is a very good point, I bet he did have it open. His report said "bench tested". Well thanks very much for your help I will have another chat with the guy.