Squealing tube amp...

[Fisheth]

So, I've got a Ashdown CTM100 valve head here and all of a sudden it starts making crackling noises and then squealing.

The VU meter is going nuts and has it's little pointer up about half way.

Could this be a Power Tube that's gone? I have a new set of tubes here, but I don't want to put them in if I'm just going to find that they blow straight after I've biased them.

[Billy Apple]

It could be all sorts of stuff. I'd get it to a tec.

[ColinB]

I'd try contact cleaner in the valve sockets first.

[b]Switch off amp and let the valves cool down[/b]; remove valve; spray cleaner (NOT WD40); replace valve with a slight circular wiggle motion to scrape the contacts together.

Then, if this doesn't work, try swapping the pre-amp valves (the small ones) around and see if that makes a difference. If it does, you'll need to swap out a pre-amp valve.

If any this makes no difference... take it to a tech.

[EliasMooseblaster]

From the fact you've mentioned 'squealing' very specifically, I wonder if it might be dirt in one of the pots on the front. Very different beast, but I have a knackered old solid-state amp that crackles and squeals when I play with the parametric EQ control - could be something similar in this case, that you could very easily test.

Though as Sean says, best get it to a tech!

[Fisheth]

[quote name='ColinB' timestamp='1479814446' post='3179438']
I'd try contact cleaner in the valve sockets first.

[b]Switch off amp and let the valves cool down[/b]; remove valve; spray cleaner (NOT WD40); replace valve with a slight circular wiggle motion to scrape the contacts together.

Then, if this doesn't work, try swapping the pre-amp valves (the small ones) around and see if that makes a difference. If it does, you'll need to swap out a pre-amp valve.

If any this makes no difference... take it to a tech.
[/quote]

Yeah, had a suspicion it was a preamp tube.

I'll try this, if it fails I'll take it to Stoneham again.

Needs a service anyway!

[Beer of the Bass]

Do any controls affect the volume or tone of the noise? Is the noise present on the effects send, or just on the speaker output? Working that out will help you to pin it down to one part of the circuit.

Edited November 22, 2016 by Beer of the Bass

[Fisheth]

[quote name='Beer of the Bass' timestamp='1479818477' post='3179494']
Do any controls affect the volume or tone of the noise? Is the noise present on the effects send, or just on the speaker output? Working that out will help you to pin it down to one part of the circuit.
[/quote]

Doesn't make a different, noise is still there and my cat hates it.

Gonna take it to a tech I think.

[ColinB]

I'm not sure what the tech will be able do with your cat!

[Bigwan]

[s]I'd maybe approach this a little differently if none of the cleaning works. Try pulling each preamp valve in turn, starting with the first one (they're usually numbered V1 - V?) and switching the amp on to check if it stops the problem. This won't do the amp any harm, but should isolate the issue to a certain section of the circuit. Don't blindly swap valves either - note that you're swapping like for like. Their are 3 different flavours of preamp valve in there for a reason...[/s]

Just reading that last comment again - if your volume control makes no difference it probably isn't in the preamp...

Edited November 22, 2016 by Bigwan

[Fisheth]

Seems to be a Power Tube, changed some tubes and it's not been squealing, going to try Colin's suggestion again and take it to Martin at Stoneham anyway. Might be something seriously up.

[Twincam]

Squealing is normally from the valves. And not uncommon. If you replaced a tube or so and its stopped, I would say a trip to an amp tech is probably a waste. Not that I'm saying you shouldn't. Its always good to have something checked over.
Seems like it was just a tube issue.