[GEAR] Marshall JTM60 Amp repair
So I thought I would share this fix for my amplifier. I've had a Marshall JTM60 for about 7 years now I picked up used for around 600 bucks.
If you ask anyone who's owned one of these you're gonna find a few things out. One being that they tone is out of this world. It's 60 watts, it can handle club gigs no problem. Perfect for jamming with the band but two, there are a lot of complaints out there regarding this amplifier's durability. They seem to have a few design flaws that cause a lot of issues users for players who own them. Myself included obviously.
The main thing is that heat from the tubes vents right up into the electronics and causes failure. Solder connections get too hot and can melt causing contact issues. The transformers in mine have already been replaced prior to my purchase but after a while, I started noticing the amp would have these volume cutouts.
Naturally I took it to the repair shop. The charged me 300 bucks to solder a new tube socket on, which he didn't do that great of a job, and re-tube and bias the amp.
After I'd got it back, I made a huge mistake. I didn't fully test it out and let the warranty on the work expired. I basically left it in the studio after a 20 minute jam session and didn't end up back in there for a few months while I was on a break. The volume issue was still there and I basically went out and bought 3 new amps going back and forth between them trying to be happy. I tried all kinds of amps. I even bought an Orange 30 watt combo that cost me nearly 1700 bucks. That, I sold last year because I just wasn't happy with the tone.
Naturally now that I have kids, I don't have that kind of money any longer. I'm pretty tech savy and work in computers so I was comfortable opening it up on my own this time.
ELECTRICAL SHOCK AND SAFETY WARNING!!! PLEASE BE WARNED! DO NOT OPEN AN AMP UP IF YOU DO NOT KNOW WHAT YOU ARE DOING. YOU CAN GET ELECTROCUTED AS CAPACITORS AND TRANSFORMERS CAN STILL HOLD A CHARGE EVEN AFTER THE AMP HAS BEEN OFF FOR A WHILE. DO THIS AT YOUR OWN RISK.
I went out on the internet and started researching the issues. I'd like to thank mrgretschfalcon over at Youtube for posting his fix. Here is a link to his video showing it off. Nice guy! https://www.youtube.com/watch?v=Vs2TRFz-2RI
Most folks have installed fans or had them installed. That is an option but typically you want the tubes hot so this can lead to a degradation of sound quality which really defeats the purpose. This is my take on it.
As you can see, above the tubes, there is now a heat plate installed so the heat doesn't damage the electronics. His video shows 3m velcro holding it in place but he did update it saying he had to install some screws instead as the velcro didn't last. It is aluminum and quite thick. I used what I could find which was actually an old sign a guy at work had as scrap. Cheap and easy. I used a ban saw after measuring and cut it. I stripped the sign's paint off using standard paint stripper. Then I marked the holes on it and hit it with a drill. Found some bolts and nuts and just installed them using the vent grill on the amp. I did not have to do any drilling at all on the amp so this is reversible if need be. I bought a few rubber washers to go in between the plate and the grill so there's a space and made sure the plate did not touch the tubes in any way.
After tightening the bolts, I used a drop of super glue on them to hold them in place. Had to wait 24 hours for the glue to cure as it was putting off a smell right after installation when I turned the amp on. It went away the next day.
This is the first part of the fix. This will prevent future issues from happening related to heat. Other's have said online in many forums that Marshall amps have a tendency to cutout the volume. This is due to the FX loop connections on the back. Some contact spray cleaned those right out. I've yet to have any issues with it. I did all the pots while I was in there too, which is always a good idea when you have the contact spray out.
All in all, this is a great sounding amp with some flaws but thus far it's running like a champ now. It cost me about 30 bucks to do, and a few hours of my time.
If you know what you're doing and are comfortable and happen to have one of these, I highly recommend this fix as the amp sounds fantastic and I believe I'll get a lot more use out of it now.
If you can find one cheap enough, this might be a great way to get into a great sounding tube amp.
Posted May 15, 2016, 8:18 PM UTC