Question about noise during amp warm up...

[mcbrideb78]

Ok, so I have two Class 5 heads. One I purchased new and the other used. They both sound the same once warmed up. However, the used one makes some radio static type noises during the first 30 seconds of warm up and then goes away and it's fine after that. Volume changes do not affect the sound as it does it the same way whether the volume is all the way down or up. Once it's warmed up there are no strange noises at all.

I thought it was just going to need some new tubes, so I didn't worry about it, but as a test I just swapped the tubes in from the other head, but it still does it. It's a clean head and the tubes were the original Marshall labeled tubes, so I don't think it's been messed with.

Any recommendations on what the cause might be? I was thinking of pulling the chassis out and checking all the mechanical plug in connections first.

Thanks.

[Anitoli]

Ok i just mulled over the schematic and i see this has no standby.
It sounds about the same time it takes for the heaters to warm.
If its not a tube im thinking something related to it such as a capacitor.
You could remove both preamp tubes and see if it stops. if not replace and remove the el84 and see if that makes it stop. Or you could try it one at a time. By removing the tubes your breaking the signals conducting path, this can help isolate the part of the circuit its in.

[mcbrideb78]

Well after removing the tubes and putting them back in again, the noise is pretty much gone. I'm betting the power tube socket is a bit dirty, and working it a few times has cleared some of the corrosion. One of these days I'll have to pickup some contact cleaner and do a proper cleaning.

[mcbrideb78]

Just thought I would update this thread to say that after cleaning the power tube socket and checking the various non-soldered internal connections and putting it back together that the noises are gone. So, a bit of simple maintenance solved the issue.

Edited to add that I used a little bit of rubbing alcohol not contact cleaner to clean the tube socket.