JCM2000 TSL Power Transformer

[Enzo]

So, the bulb limiter is for troubleshooting only? Then bypass it once I am sure there are no major shorts or power related issues?

Yes exactly.

What I was being adamant about was if you wire the primarys out of phase, they will act like a dead short circuit. It won't cause kinda low voltages, unless the zero voltage of a blown fuse counts.

[mikeboone]

Thanks Enzo. I was so paranoid. I traced it out on the schematic and drew myself a connection diagram, then went out to the amp and worked it out visually and made a diagram. They matched, no smoke or bright bulb

[mikeboone]

Last issue was a preamp tube socket that needed to be re-tensioned. One pin was spread a bit and was intermittent. It looks to have good memory after adjusting. I plugged in a tube, pulled it out and it drew back in like the others.

Thanks for all the help guys. I really do try to try as much as I can before asking you guys to spend your time babysitting me. Thanks for everything.

[davetutt]

Please be aware that the transformer failing is potentially the start of a long and painful refurbishment of these amps. You will find that there is a complete minefield of work if it had a suspect version of the main valve board ie the one that carries all the valve bases. I have seen quite a few of these amps over the years and if you have a revision 3,5 or 7 board (its marked on it in white lettering) then you need to know about the failure of the printed circuit board material with internal leakage and how this causes runaway bias and valve failure. There is also an issue with thermally unstable resistors in the entire board but especially under and around the el34 output valves. If it is a rev 5 board you will also find that the grid stopper resistors are 220k rather than 5k6 and are at best half watt resistors when they should really be 1 or 2 watt. This adversely affects the amp tone particularly in the clean mode making the amp sound strangled and lacking drive.
I have had several of this model with blown mains transformer as a result of failure of the crucial parts on the valve output pcb stage and just doing the transformer is not the correct thing to do. You need to go further! For the transformer to fail it has to be under excessive strain and the only cause of this is the loading from the output stage.
Hope this helps. These amps are not the best in terms of reliability because of their drifting bias and as most players are only to aware of the dead on stage situation cannot be trusted unless they are extensively worked on to sort out the design and manufacturing failures of some 14 years ago! An untreated amp will only last around 6 loud gigs before it needs new output valves because they have been over driven.

[mikeboone]

Thanks for the feedback, Dave. I actually advised this that he would need to take it to New Orleans where there is a Marshall authorized service center for any additional work. I build simple amps, 2204, 1987, Orange, Fender, etc type stuff as a hobby and by default I can fix the common problems that ail a lot of old amps. I am not by any means a commercial electronics shop with the experience and resources of you professional guys. There are very very few people in the is area who know anything about tube amps so I do what I can to help them out. The only other guys around that know are fellow hobby builders and wont touch a repair with a 10 foot pole. I can promise I am the least expensive amp fixer-upper around. I charge cost for parts and either pizza/beer or a little cash for labor.

[davetutt]

no problem Mike.

If you get problems you need help with either stick something here or send me an email. dave_london@hotmail.com

I do all sorts of repairs here in a little place called Chatham, Kent UK just to the east of London. I never intended what was a side line to become a full time job having been an IT specialist for best part of 22 years. Having been pushed out of my job at the BBC maintaining some very expensive broadcast TV engineering hardware and software and having been put in a situation where I was never going to work in the same field again I had to fall back on what I know. Having repaired things for over 40 years (I started when I was in my teens) I thought it best to use my skills. Not that it makes any money! If you have to spend 90 UK on a transformer and 70 UK on a output tube set plus, depending on how bad it is anything up to three days repairing all the nasty things that Marshall throw into the mix its never going to be a cost effective way of earning a living! Oh well, back to a Marshall 100 watt MOSFET head that happily goes into instability if you dare to set the controls where it doesn't like them!

Regards

Dave

[StewartM]

Hi.

I am installing the same Classic Tone PT into my TSL and also had a question about the added heater ground wire. I shot an email off to CT support, and I was told to ground the wire to chassis, but no mention was made to remove R8 and R78.

Could you please explain why you can't use both ground schemes at the same time? Does it have to do with a potential ground loop?




Thanks for the info,

Stewart

[StewartM]

Ignore my reply on instructions to attach the heater ground to chassis. There was some confusion that has been resolved.