How hot should power tubes get?

alan67

alan67

Well-known member
Picked up a 100 watt JCM2000 DSL a few months ago. Haven't really played it too much until last night. After about 30 minutes, I noticed kind of a slight smell coming from the amp, not really electrical though - hard to describe. Anyways, I put my hand on top of the amp and the plastic vent over the power tubes was really hot to the touch. Unplugged it, took off the back and looked inside, couldn't see anything that looked abnormal. It's been a long time since I've had a Marshall head so I don't remember if this was normal or not.
 
Probably nothing to worry about.

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DSL's run hot, and depending on the year of production could have issues. Mine runs fairly hot and I've got the bias lower than what Marshall specs, and it sounds great.
 
Doug's Tubes told me they really like to burn in tubes during the winter.
I guess the room gets dry sauna hot.

I can stick a small fan towards the back of my Diezel Herbert and feel the heat 10 feet away.
 
SDMF38":1hl43jeq said:
DSL's run hot, and depending on the year of production could have issues. Mine runs fairly hot and I've got the bias lower than what Marshall specs, and it sounds great.
Click to expand...

I'm finding that to be the case. Everything I've read mentions these amps typically being biased pretty hot.
 
I just posted this in another thread but it could be a 'known' issue with some of the earlier ones. Basically the board gets slightly conductive as it gets hot and then the screen voltage mucks with the bias voltage (since the traces are adjacent to each other at the tube socket) and the amp just gets hotter and hotter. Here is a page on it.
 
I picked up a 2000 JCM 2000 a month or 2 ago. I've spent a lot of time under the hood changing caps and doing mods. Just this weekend I did a PCB mod to the main board to resolve a bias drift issue some of the early ones had. The bias drift is caused ultimately by the heat making some of the board traces conductive. DSLs (and TSLs) definitely run hot. The most important thing to do is measure your bias over the course of an hour and see if it keeps going up.
 
I could keep a grilled cheese warm all night with my Marshall. Toasty !!!!!!! It is supposed to smell hot. That's when you have a good Marshall with Mojo. As long as it is not an electrical burning smell you should be okay. You will know when that happens because it is a very unique smell.
 
John4021":8or4qmk4 said:
Doug's Tubes told me they really like to burn in tubes during the winter.
I guess the room gets dry sauna hot.

I can stick a small fan towards the back of my Diezel Herbert and feel the heat 10 feet away.
Click to expand...

You've got 6 nice bottles in that puppy! I remember when I had mine, I could heat my basement studio area! It was great!

:D
 
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