JCM800 2205 head (lotsa pics +gutshots) - help needed!! [Archive]

View Full Version : JCM800 2205 head (lotsa pics +gutshots) - help needed!!

fusebop

10-31-2008, 03:14 PM

http://farm4.static.flickr.com/3275/2990101370_1587a61a82.jpg
To say that qualified tube amp techs are rare here in Serbia
is a serious understatement. So please help me if you can.

http://farm4.static.flickr.com/3220/2990105484_b246a080e8.jpg

http://farm4.static.flickr.com/3201/2990105490_7d7264604a.jpg
I bought this JCM 800 50w head with spring reverb for $500.
Cosmetically pretty nice condition, I'd say, and the amp
works although the pots are terribly scratchy. The amp also
runs on 6L6 type valves.

http://farm4.static.flickr.com/3233/2990105496_d55188bb86.jpg

However, the previous owner was kind enough to let me know
that there used to be an arcing problem going on around the
power tube sockets (we're about equally ignorant about these
things), which supposedly fried a few 6L6's in its time. The
amp hasn't been played for at least 5 years.

http://farm4.static.flickr.com/3172/2990105500_2452a63214.jpg

http://farm4.static.flickr.com/3050/2990105510_0919e34bf0.jpg

http://farm4.static.flickr.com/3176/2990105512_1af4aab4ca.jpg

The test run went fine but I don't want to endanger anything
and I will be taking the amp to a tech. The problem is, the
nearest good technician is 150 km away.

http://farm4.static.flickr.com/3207/2989254979_41e924993e.jpg

http://farm4.static.flickr.com/3225/2990109262_7a70c93d78.jpg

http://farm4.static.flickr.com/3283/2989255407_733cf4a222.jpg

http://farm4.static.flickr.com/3237/2989255683_a34fe9844c.jpg

That's why I need your help, for now:
1) how does this look on the inside?
2) Do you think the components are all original?
3) Are there noticable signs of previous malfunctions/damage?
4) The preamp tubes and filter caps were NEVER changed.
I think they are possibly from '84. Any suggestions,
what brand/models should I be looking at?
5) Should I spray contact cleaner and work the pots a bit,
or simply buy new pots? Which ones, what values?
6) Did I overpay or underpay this amp? I'm in love with
the awesome megalithic crunch it's producing anyway.

If the pics don't work here's a link for the flickr set:
http://www.flickr.com/photos/27627977@N04/sets/72157608545107259/

Sorry if my english is a bit weak, and thank you if you will
endure my awful photography skills and give me some answers!

Dave C

10-31-2008, 07:33 PM

Your english is very good and your photography isn't bad either. Your amp looks to be in good condition inside and out. I don't see much if anything in regards to repairs or component changes from the pictures.

I would spray some tuner cleaner in the pots to clean them up and only replace the ones that don't clean up. Values of components are usually on the components themselves or are available from the schematic.

My only question on your amp is since 2205's usually use EL34 power tubes and yours has 6L6's...and I don't see any evidence of changes on the board in the area of the bias circuit. Has your amp actually been set up to use 6L6 tubes? This could be the reason it has "fried" a few 6L6's over the years.

I think you got a good deal on the amp overall. I would suggest spending a bit of what you saved having the amp properly checked out...especially the range of the bias circuit if you continue to use 6L6's. A cap job and some new preamp tubes wouldn't be out of line either.

Looks like you got a good deal on a good amp and with a modest tuneup, it'll be even better. Good luck.

wallaceSnr

11-01-2008, 09:34 AM

my only question on your amp is since 2205's usually use el34 power tubes and yours has 6l6's...and i don't see any evidence of changes on the board in the area of the bias circuit. Has your amp actually been set up to use 6l6 tubes? This could be the reason it has "fried" a few 6l6's over the years.

+1.

phsyconoodler

11-01-2008, 12:22 PM

RedMan

11-01-2008, 01:50 PM

I'd clean the sockets and put EL34's in if that's what it came with, then bias it up. Should be OK then

pfrischmann

11-01-2008, 03:02 PM

Yeah. the 6l6 thing is wrong...as far as I know....el-34's yes. 6550's in the us...yes but the pin config for each is the same.

Look really carefully on the tube pins and the tube sockets, if there is any sign of carbon, they need to be replaced or it will happen again. This is a great way to take out an OT.

FortinAmps

11-03-2008, 10:00 AM

If there is an 'arcing' problem around the power tube sockets there are likely carbon traces on the tube sockets.Pull the power tubes and look for black on the sockets.Lots of light and a magnifying glass.If there is any sign of carbon the sockets will need to be replaced.If a power tube shorted at one time it is very likely that is the issue here.

+1, Great advise.

If you can't easily get a replacement socket, you can use a small flat headed screw driver and scrape away all the black carbon. You should be good to go after that. :dude

Cheers,
Mike

fusebop

11-03-2008, 10:47 AM

I can't express how grateful I am, guys. Thank you, you rock!