These amps are well known for their cheap construction, and over heating problems. The most common problems are blown transformers, and short valve life. Anyway, I own two of these and like them a lot, except that they constantly overheat, and stop working after more than an hour of constant use. After a few minutes turned off, they come good again, so it's not a permanent fault every time they appear to blow.
Is there any way to stop this overheating, short of adding a cooling fan to the chassis?
Could components be changed to lower the voltages that may be causing the heat, like lowering the B+ voltage, or biasing differently?
How can they shut down when hot, but come good when they cool again - what component could cause this, without permanent damage to itself?
Should any components be upgraded to ones that will work at higher temperatures, or would this strain the weaker components?
Marshall JTM30/JTM60 overheating problems
Moderator: jingle_jangle
Marshall JTM30/JTM60 overheating problems
Two wrongs don't make a right, but three rights do make a left.
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soundmasterg
- RRF Consultant
- Posts: 1923
- Joined: Tue Oct 01, 2002 1:06 pm
My offhand guess would be that the power tubes are biased too hot, or that some resistors are under spec (they should be 1/2 watt instead of 1/4 quarter watt). That is strange that it shuts down when hot but then works again soon after without blowing a fuse or something. I'd guess there must be some solid state stuff in there in addition to the tubes that must be overheating. It needs to be taken to a tech who is either familier with this particular amp and it's prolems, or to a tech who can put it on the bench and try to make it fail by heating up parts. Once he knows which parts are overheating, some solution could be improvised. I've never seen one of these particular amps myself so thats about all teh advice I can offer.
Because you didn't like the sound, or because it kept breaking down?
BTW, I found an article on the web titled:
"Fixing the infamous bridge rectifier / heater wire problem", and, although it refers to a JCM2000 DSL201, the symptoms are identical to my JTM30.
http://www.piller.at/music/dsl201/ (Why doesn't HTML code work after a forum post is been edited?)
BTW, I found an article on the web titled:
"Fixing the infamous bridge rectifier / heater wire problem", and, although it refers to a JCM2000 DSL201, the symptoms are identical to my JTM30.
http://www.piller.at/music/dsl201/ (Why doesn't HTML code work after a forum post is been edited?)
Two wrongs don't make a right, but three rights do make a left.
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byrdwatcher
- Veteran RRF member
- Posts: 11
- Joined: Sun Mar 03, 2002 11:06 am
Hello--
I'm just a recreational player, and don't gig... but I've had a JTM 30 (the 2 x 10 model) for six years, and I've never had any problems with it. I've read that Marshall cancelled this product line due to transformers overheating, but so far, so good with me.
My amp is regularly on for more than an hour, with no problems. I've retubed it once with 5881 power tubes (along with the appropriate preamp tubes), which is what it had when I got it. An online tube merchant told me that these amps came from the factory either with EL34 or 5881 tubes. He also said they're "self-biasing," but from Jared's posting it looks like the tube guy didn't give me a straight story.
I have absolutely zero knowledge of tube amps, but at all times mine is plugged into a voltage regulator/power strip. Maybe this helps... who knows?
In any case, I bought this amp because it had the best clean AND dirty tones of any tube amp in its price range. Granted, I've never plugged into a Matchless, a Bogner, etc. But I've still never heard anything that comes close to the JTM 30. A good friend has a Riviera 2 x 12 head/cabinet setup as well as a Top Hat 2 x 12 combo, and the Marshall smokes 'em both. I, for one, am very pleased with my amp.
I'm just a recreational player, and don't gig... but I've had a JTM 30 (the 2 x 10 model) for six years, and I've never had any problems with it. I've read that Marshall cancelled this product line due to transformers overheating, but so far, so good with me.
My amp is regularly on for more than an hour, with no problems. I've retubed it once with 5881 power tubes (along with the appropriate preamp tubes), which is what it had when I got it. An online tube merchant told me that these amps came from the factory either with EL34 or 5881 tubes. He also said they're "self-biasing," but from Jared's posting it looks like the tube guy didn't give me a straight story.
I have absolutely zero knowledge of tube amps, but at all times mine is plugged into a voltage regulator/power strip. Maybe this helps... who knows?
In any case, I bought this amp because it had the best clean AND dirty tones of any tube amp in its price range. Granted, I've never plugged into a Matchless, a Bogner, etc. But I've still never heard anything that comes close to the JTM 30. A good friend has a Riviera 2 x 12 head/cabinet setup as well as a Top Hat 2 x 12 combo, and the Marshall smokes 'em both. I, for one, am very pleased with my amp.