Hey first post here and I thought I would share my '88 JCM 800 2204 that I bought in the early 90's and have used in about 5 bands since then of many genres.
I do recall taking the amp for service in '98 in NYC at EARS but I don't recall what was done. Since then the amp has been played weekly for at least 4+ hours a week at a rehearsal space or live and all I did was change tubes a few times. With the lack of rehearsals etc lately I decided it would be a good time to bring the amp home blow out decades of dust and look inside. I Haven't done a cap job before but pretty handy with electronics and soldering (yes I have discharged filter and bias caps and have confirmed with a multi meter).
I see these are original style LCR caps but were they ever replaced? Is anything look to be changed inside? The markings in the corner "470/38.5" is that the bias setting or a factory note?
The amp sounds good but on some occasions I thought maybe there were some inconsistencies from one day to the next.
I have ordered the F&T / Sprague cap kit and will be doing that soon. Enjoy the pics!
JCM800 2204 owned since '94
Moderators: pompeiisneaks, Colossal
JCM800 2204 owned since '94
You do not have the required permissions to view the files attached to this post.
Re: JCM800 2204 owned since '94
You do not have the required permissions to view the files attached to this post.
Re: JCM800 2204 owned since '94
You do not have the required permissions to view the files attached to this post.
Re: JCM800 2204 owned since '94
I'm an amateur. It is possible someone will correct me 
The caps appear to be date coded 87-50 and 8705. I read this to mean 50th week of 1987 and 5th week of 1987. This makes it likely the date of manufacture was early 1988. If that makes sense, the caps are, in all likelihood, original. Anyway, 33+ year old caps should probably be replaced.
470/38.5 probably means plate voltage = 470VDC @ 38.5mA. It is likely bias voltage is around -57V. If you confirm both voltages, then this is very likely correct. However, if you swapped tubes without checking or adjusting bias, this could easily be off from those numbers a bit.
The caps appear to be date coded 87-50 and 8705. I read this to mean 50th week of 1987 and 5th week of 1987. This makes it likely the date of manufacture was early 1988. If that makes sense, the caps are, in all likelihood, original. Anyway, 33+ year old caps should probably be replaced.
470/38.5 probably means plate voltage = 470VDC @ 38.5mA. It is likely bias voltage is around -57V. If you confirm both voltages, then this is very likely correct. However, if you swapped tubes without checking or adjusting bias, this could easily be off from those numbers a bit.
Re: JCM800 2204 owned since '94
thanks for that info I was wondering if those were the date codes '87" on the LCRS. Yes I have probably been through many sets of tubes since that service date.
I do have the bias adapter I bought from JJ tubes but have Never biased an amp.
I do have the bias adapter I bought from JJ tubes but have Never biased an amp.
Re: JCM800 2204 owned since '94
Sure is clean on the inside. You'd never know it was over thirty years old.