I have a Marshall DSL 401 (40 watts) tube combo amp. The amp will
play fine, but then two of the small tubes inside will go dark and
then all the sound goes away. I'm pretty sure these are pre-amp
tubes.

Both tubes go on and off together, which leads me to believe it has
something to do with the electronic circuit that is feeding these
tubes rather than just having a bad tube.

Does anyone have an idea on this or what I should do?

Paul Newman wrote:

I have a Marshall DSL 401 (40 watts) tube combo amp. The amp will
play fine, but then two of the small tubes inside will go dark and
then all the sound goes away. I'm pretty sure these are pre-amp
tubes.

Both tubes go on and off together, which leads me to believe it has
something to do with the electronic circuit that is feeding these
tubes rather than just having a bad tube.

Does anyone have an idea on this or what I should do?

Filament supply fault (probably). Should be an easy fix.

Regards, Dan.
--
And on the evening of the first day, the lord said.... LX1, Go!
And there was light.
The email address *IS* valid, do not remove the spamblock.

In article ,
(Paul Newman) wrote:

I have a Marshall DSL 401 (40 watts) tube combo amp. The amp will
play fine, but then two of the small tubes inside will go dark and
then all the sound goes away. I'm pretty sure these are pre-amp
tubes.

Both tubes go on and off together, which leads me to believe it has
something to do with the electronic circuit that is feeding these
tubes rather than just having a bad tube.

Does anyone have an idea on this or what I should do?

Don't **** around. Take it to an experienced tech.

Well worth the money not to fry yourself on high internal voltage.

CT

Paul Newman wrote:
I have a Marshall DSL 401 (40 watts) tube combo amp. The amp will
play fine, but then two of the small tubes inside will go dark and
then all the sound goes away. I'm pretty sure these are pre-amp
tubes.

Do you know if they have DC filaments or not?
Series string or paralleled?

Both tubes go on and off together, which leads me to believe it has
something to do with the electronic circuit that is feeding these
tubes rather than just having a bad tube.

Well, with the filament circuit anyway.

Does anyone have an idea on this or what I should do?

If you aren't even sure if they are pre-amp tubes, you probably don't
want to be poking around with a voltmeter. If this is a series string,
you probably have a bad connection somewhere on the filament string.
If it's got DC filaments, it's probably something wrong in the DC
supply, like a bad rectifier. But it's in the filament supply and it
is something common to both tubes but not common to the finals.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."