Distortion after 15mins use

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Distortion after 15mins use

Post by Axeman010 » Sun Apr 18, 2021 7:31 am


I built my JTM45 approximately 7 years ago and in that time it has not had a great deal of use as it stays in my studio as a recording amp.

Whilst recording recently I noticed that after approximately 15 minute or so, from cold and with a clean dialed in sound the signal starts to break up in to a light distortion sound a bit like a crunch setting. Volume pots are on 2 or less when this happens. After this time its nearly impossible to get a clean sound

I guessing this is a heat related problem but as this has never happed to me before I'm not sure if this is just a valve gone bad or possibly a dry joint opening up with the heat. Hopefully its not a transformer problem !

I would be most grateful if anybody has any advice on diagnosing this problem further.

Thanks in advance


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Re: Distortion after 15mins use

Post by danman » Sun Apr 18, 2021 7:02 pm

I would say that either of those possibilities could be causing the problem. Try swapping in a fresh preamp tube through each spot to see if it helps. Do the same with the power tubes if you have a spare set. Don't forget to check the speaker also. If these ideas don't help, try chopsticking all of the solder joints with the amp turned on. Listen for any static or strange noises when you press against the wires and joints. There are a few places in the circuit that may make a small popping sound through the speaker when poked at but you are mainly looking for static or crackly sounds when performing this test. If all of this fails, a full list of all voltages will help to see if there is a problem within the circuit.

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