Artisan 15H crackly output........

Neckwringer

After about 20-30 mins playing the volume starts to drop and then there is bad crackly like distortion,this starts on channel 1 and when you go to channel 2 it soon catches up and its off again....
Could this be the output tubes by any chance?.

ecc83

Not output valves because they are common to both channels, in fact considering the topology of the circuit I cannot immediately think of a cause that would start on one channel then go to the other. You could try swapping the input ECC83 with the PI valve? In fact, pull the first two valves, '83 and EF86 and see what happens.

I suspect however that someone is going to need to investigate with a 'scope.

Dave.

Neckwringer

Its highly likely that both channels start distorting at the same time instead of 2 following 1 thinking about it,would this lean towards the output tubes if so?.

ecc83

Neckwringer said:

Its highly likely that both channels start distorting at the same time instead of 2 following 1 thinking about it,would this lean towards the output tubes if so?.

In that case, pull the PI valve and run the amp. No noise? NOT the OP bottles.

How old is the amp? If a very early one it might still be biased a bit hot for some valve brands,

Dave.

Neckwringer

ecc83 said:

Neckwringer said:

Its highly likely that both channels start distorting at the same time instead of 2 following 1 thinking about it,would this lean towards the output tubes if so?.

In that case, pull the PI valve and run the amp. No noise? NOT the OP bottles.

How old is the amp? If a very early one it might still be biased a bit hot for some valve brands,

Dave.

Is that the first el84 after the preamp tubes..?

DartmoorHedgehog

Neckwringer said:

ecc83 said:

Neckwringer said:

Its highly likely that both channels start distorting at the same time instead of 2 following 1 thinking about it,would this lean towards the output tubes if so?.

In that case, pull the PI valve and run the amp. No noise? NOT the OP bottles.

How old is the amp? If a very early one it might still be biased a bit hot for some valve brands,

Dave.

Is that the first el84 after the preamp tubes..?

It won't be an EL84, more likely an ECC83/12AX7 type. Probably the nearest "preamp" valve to the power valves, but somebody will hopefully be along soon to tell you exactly which.

Neckwringer

Anyways I played it yesterday without the attenuator and after 20mins the volume started to spike and it was fuzzn n a buzzn for a couple of minutes as I played thru it,then it settled down and I played on for an hour without a problem.
Played again tonight with the attenuator and it was fine so don't know what was going on with it......