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Playing through my JTM30, heard a pop, then nothin!!!

BurstBrian

New member
Joined
Feb 5, 2005
Messages
1,179
I love this little amp. Bought it way back and it's been a great amp for me at home. Recently when I was using it, I heard a pop and then nothing. The believe tubes were original and I though that might be the issue. I replaced them but still nothing. Any ideas??
 

jrgtr42

Well-known member
Joined
Mar 24, 2005
Messages
2,308
Did you check the fuse?
With luck, it's that simple. If not, you might have blown a cap or resister - or if really unlucky, a transformer.
If you're handy, you might open it up to take a look and see if there's something obvious. But if not, then don't - take it to a repair place.
Amps have a lot of high voltage lurking in there, even if powered down / unplugged, and can give you a hell of a jolt if you're not careful.
 

Mars Hall

Active member
Joined
Nov 26, 2008
Messages
1,829
They sound awesome but a poor design issue makes them prone to over heating. Most tube amps have the tubes mounted vertically, the JTM30 and JTM60 models from this era all have the tubes mounted horizontally directly under the circuit board. All the heat generated, from the largest surface area of each EL34 power tube, bakes all the components.

My recent experience, with a JTM30 2x10 model, caused the output transformer to burn up. Once you have it repaired, highly recommend using a fan, pointed at the back of the amp, to dissipate the heat. I've heard of some mounting cooling fans internally but it required drilling holes in the cab for ventilation. It's really too bad about this design flaw because, like I said, these are really good sounding amps and can be found very reasonably priced.
 

el84ster

Well-known member
Joined
Sep 10, 2001
Messages
1,420
I’m a tech.
Sounds most like high current draw blew something. Hopefully just an old power tube (don’t leave those in there until they die, they can take something out with them) that pooped the fuse. New tubes, new fuse and you might be good to go. If not, it’s time for pro help. Most often it’s tubes then next often is power supply Problems.
 

Bob Womack

Well-known member
Joined
Apr 8, 2002
Messages
2,191
I own one one these horrible designs. Darn thing only lasted for twenty-five years on the first pair of power tubes before it went POP and then went silent. It blew a power tube and a couple of resistors. Sucker cost me parts and an hour of bench time. Unforgivable. Unacceptable.

marshall3.jpg



Obviously I'm being facetious. It is a JTM612 and it has served me really well. Right now I am using it as a power amp for my Helix. The repair cost me all of $124.50 including a new pair of ES-34 power tubes, a fuse that lives on the motherboard, and the two of resistors that cooked off when the power tube died. I'd say that was entirely acceptable working costs after twenty-five years of service, wouldn't you? But you wouldn't think such a record could exist for all the whining about the latter-day JTM line.

I went through this little song and dance to give you an idea of what it will cost you. Oh, and I like the sound of the JTM30!

Bob
 
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