dsl201 no voltage on preamp tubes

[mark enger]

I got a marshall dsl 20 watter it has some problems, powertubes seem to be getting power but none of the preamp tube are getting high voltage to the plates, im not real good with these printed boards, the clean/od lights are not working could this be stopping the power supply to the preamp tubes? any suggestions would help thanks mark

[Prairie Dawg]

Does your phase inverter tube (V4) get power? Looking at the schematic, the other three tubes get filament power off of a diode bridge that is pretty famous for failing. It's marked BR2 on the schematic.

The good news is that you can buy a serviceable diode bridge for these amps at your local Radio Shack for about three bucks. It's best to install them up off the board a little and also you can attach a small heat sink while you're at it.

That'll get you filament voltage if that's what you're needing.

As far as B+ (or HT if you're British), check your F1 fuse (250 ma), because that shuts down everything downstream of that. I'll bet you don't have plate voltage anywhere if it's blown. You can follow this right out on the schematic.

If that's the problem you may likely have a shorted EL84 that caused it.

[Structo]

Check for a HT fuse.

If it has one and it is blown you should check out the amp to see why it blew.

Common things are shorted power tubes.

[mark enger]

Thanks, ill check it out mark