Marshall DSL problem?

[SLOgriff]

Recently bought a JCM 2000 DSL 100 (2009 MLB) version. Love this amp...and some killer Marshall tones! Seems to be in excellent condition and very clean with original Marshall tubes and never opened up.

Anyway, I noticed that all four EL34's power up BUT the two left pair of tubes do not come out of standby when in play mode. Meaning they don't give the blue glow as the right pair (that tubes normally do when off standby). I swapped out the tubes and still the two left pair seem to not be playing with the right pair. Hope this makes sense...

Any ideas on what might be wrong? I took the chassis out and looked inside and everything looks clean without any burn marks or blown fuses.

Thanks
Bryan

 

[311boogieman]

I'd get a probe and a mutlimeter and check them all and report back. Good tool to have anyway if you don't. I thought these amps worked as an inner pair and outer pair?

 

[SLOgriff]

I'd get a probe and a mutlimeter and check them all and report back. Good tool to have anyway if you don't. I thought these amps worked as an inner pair and outer pair?

The pairs are biased separately with one trim pot for left pair and another trim pot for the right pair. I have a multimeter, just not skilled enough to know which components to check. I was thinking screen grid resistor but they look fine with no burn marks or cracks. Not sure of a tech here in Phoenix to take it to.

 

[311boogieman]

I'd get a probe and a mutlimeter and check them all and report back. Good tool to have anyway if you don't. I thought these amps worked as an inner pair and outer pair?

The pairs are biased separately with one trim pot for left pair and another trim pot for the right pair. I have a multimeter, just not skilled enough to know which components to check. I was thinking screen grid resistor but they look fine with no burn marks or cracks. Not sure of a tech here in Phoenix to take it to.

I wouldn't take it to a tech just yet.

So no matter what tubes you put in which sockets the left pair does not seem to work? How does it sound? Sometimes there is no blue glow and tube works fine. Just sayin'

I would def check the plate voltage and bias of every socket. Test points generally cannot be trusted. The single probe from Weber is like $40 I think. Eurotubes has them for $25.

See if this helps:
http://splawnfans.proboards.com/thread/ ... g-tutorial

#9 in particular if you want to get straight to it.

Good luck

 

[1big1]

I'd get a probe and a mutlimeter and check them all and report back. Good tool to have anyway if you don't. I thought these amps worked as an inner pair and outer pair?

The pairs are biased separately with one trim pot for left pair and another trim pot for the right pair. I have a multimeter, just not skilled enough to know which components to check. I was thinking screen grid resistor but they look fine with no burn marks or cracks. Not sure of a tech here in Phoenix to take it to.

I wouldn't take it to a tech just yet.

So no matter what tubes you put in which sockets the left pair does not seem to work? How does it sound? Sometimes there is no blue glow and tube works fine. Just sayin'

I would def check the plate voltage and bias of every socket. Test points generally cannot be trusted. The single probe from Weber is like $40 I think. Eurotubes has them for $25.

See if this helps:
<span class="skimlinks-unlinked">http://splawnfans.proboards.com/thread/7786/amp-biasing-tutorial</span>

#9 in particular if you want to get straight to it.

Good luck

i have a 1998 dsl 100. i'd check the bias as well. the amp might be just fine. the sequence is 1-3 and 2-4 for the push pull on the class ab circuit.

 

[SLOgriff]

The amp sounds great at apartment levels. I just havnt had a chance to crank it up yet. Yes, swapping tubes around still only get inside power tube "blue glow" from the right two EL34's only. The left two sockets/tubes will power up as normal....just no blue glow.

Thanks for the the replies and info! Will dig into it more tomorrow.