JCM800 volume fade

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JCM800 volume fade

Post by calling card »

I got my 800 (Ceriatone) out after a couple of years or so rest. Seemed a little out of sorts, volume would fade and generally sound a bit off. High fuse blew, it was then I saw white colouration at one power valve. Changed it and a new fuse. Seems good again but the volume will periodically drop in and out. If it damaged a screen resistor when the valve went would I expect the intermittent volume issue?
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Re: JCM800 volume fade

Post by Molly »

I can't answer this for you, sorry. Just bumping because I'm interested too.

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Re: JCM800 volume fade

Post by jeremyb »

Could be another power tube on its way out?

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Re: JCM800 volume fade

Post by AiRdAd »

are the batteries starting to go flat in your hearing aids?
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Re: JCM800 volume fade

Post by calling card »

I robbed a spare JJ EL34L from my JMP clone, same valve & type. Remaining valve in 800 looks good, as I understand it white deposit up top is from vacuum leak and air getting in.
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Re: JCM800 volume fade

Post by Mini Forklift »

Chur might be able to help out if he sees this? He's a whizz with anything electronic and I believe he owns a JCM800 himself
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Re: JCM800 volume fade

Post by calling card »

I'm going to scrub the in/out jacks next. From what I've read today also run a patch lead in the effects send & return sockets. To listen for any improvement.
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Re: JCM800 volume fade

Post by RectifiedAmps »

calling card wrote:From what I've read today also run a patch lead in the effects send & return sockets. To listen for any improvement.
FX loop jacks could definitely be to blame. Also, give each preamp tube a good wiggle in its socket. Could be corrosion/dirt.

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Re: JCM800 volume fade

Post by sizzlingbadger »

Clean all the 1/4" and tube sockets, change and bias both power tubes. If that doesn't help then you'll need to start looking to see if there was any damage.
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Re: JCM800 volume fade

Post by Bg »

Then bang your head against the nearest wall for not using it for the last couple of years :P
you JUST KNOW some Tory wanker has thought of this idea already. Probably getting the inspiration whilst fucking a dead pig.

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Re: JCM800 volume fade

Post by calling card »

Yes I got distracted with Fenders. Don't think this thing liked having a rest, nice dry place it was too, maybe a bit warm in summer though.
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Re: JCM800 volume fade

Post by Bg »

calling card wrote:Yes I got distracted with Fenders. Don't think this thing liked having a rest, nice dry place it was too, maybe a bit warm in summer though.
I know, I promised myself to get my 36 watter down to an 18 watter over the last few months but house repairs got in the way. Having a helix helps.
you JUST KNOW some Tory wanker has thought of this idea already. Probably getting the inspiration whilst fucking a dead pig.

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Re: JCM800 volume fade

Post by chur »

If you run a separate preamp or pedal into the effects return bypassing the amps pre, does it still do it?
I assume you have been eyeballing the tubes during the volume drop for red plating or something?

My JCM800 could do with a volume drop :moresarc:
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Re: JCM800 volume fade

Post by Jops »

I retubed an entire amp for this same symptom, turned out it was a faulty patch cable on my pedal board :rofl:

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Re: JCM800 volume fade

Post by NippleWrestler »

When this happened with my Laney aor it was the output transformer dying.

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