Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jasonvilla on November 26, 2016, 01:28:11 am
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Hi all, I need help with a noisy jcm800 that I built before i throw it in the trash. :( I basically used the Ceriatone layout, all stock values EXCEPT the NFB is on the 8ohm tap to help tame the noise AND I have a one tube driven spring reverb, ala tubenit, thats installed. I know I know.. Ive taken it out of the signal path and moved around reverb related grounding points to try and figure out the noise problem with no success.
With the preamp volume turned up its very hissy and with the master turned up, with the pre amp turned down lower, it makes more of a hum sound. Here are pictures of the guts and voltage chart. All iron is classic tone, all tubes are JJ el34 and 12AX7s. Ive tried changing out tubes as well. Ive started to replace all signal wires with shielded cable but that hasn't seemed to help either. Hopefully someone can see something that I can't.
Any help/suggestions would be greatly appreciated! OH, and it sounds pretty good, if I can ignore the noise!
I made an album with the gut shots because I can only upload 4 images here - https://goo.gl/photos/gyRrjnDnNedK3vFu6
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I reduced the 68k input grid stopper to 10k and that seemed to take away most of the hiss but it also seems to have taken some life away. Ill try a 22k that I have on hand. Ill also play around with "enhance caps" that i saw some members talking about. :)
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Might have just been a noisy 68K R? Was kind was it, a MF, carbon film or carbon comp?
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It was just a standard carbon film like what I used everywhere else. The 10k is a metal film - for metal BUAHAHA