Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: fossilshark on May 24, 2023, 03:48:37 pm

Title: jcm800 2204 noisy
Post by: fossilshark on May 24, 2023, 03:48:37 pm

This is the JCM800 2204 I built a while ago and I was wondering if anyone had any tips to make this less noisy? Also recently it seems theres a microphonic tube so I have to deal with that as well.

When plugged into the clean channel with guitar volume all the way down + gain dimed there is only hum when the volume is up around 8 or 10. On the high gain channel hum starts becoming audible around 5 or 6.

No sane person should ever have this up past 3 but hey I just want to be prepared in case I need to play a stadium on a whim.

Any advice?

Title: Re: jcm800 2204 noisy
Post by: fossilshark on May 24, 2023, 03:50:03 pm

Heres the schematic.

Title: Re: jcm800 2204 noisy
Post by: pdf64 on May 24, 2023, 06:08:53 pm

Maybe the valve in V1 has excessive leakage between heater and cathode?
The lack of full cathode bypass / heater elevation / DC heater makes that leakage apparent.

Title: Re: jcm800 2204 noisy
Post by: fossilshark on May 25, 2023, 09:22:14 am

So mabey I should add a bypass cap? I'm thinking I want to hotrod it a bit anyways since the clean channel is so insanely quiet compared to the gain channel.