DSL 401 Help/Advice

[DiezelAmpPlayer]

Hello,

I have a Marshall DSL 401 that's around 8 years old and it's been down for a while now. I've changed the pre-amp tubes, power tubes and it's still dead.

The problem is that the power tubes and the V1 or tube closest to the input jack all turn on/light up fine but the other 3 pre-amp tubes don't. I can't remember if I've changed the fuses but I doubt that's the problem since the power tubes are on and light up well and the amp does turn on it's just that there's no sound at all.

Does anyone have any experience or advice for me (again, 3 pre-amp tubes don't light up/turn on but the V1 does and so do the power tubes) with this. Is this worth taking to a tech to fix? Is it a common problem with these amps? I really don't want to spend more than $200 to fix it and if it costs over that, I'll just dump it and get a new practice amp. I don't want to fix this thing every few months or so and I hear alot about these amps having lots of issues with heat etc.

Thanks in advance.

[Enzo]

Don't believe everything you hear or see on th einternet. These amps may have more failures than others in certain areas, but that doesn't mean they ALL drop dead once a week.

First, turn off the room lights and look at those tubes in the dark. The heater on some tubes does not stick out far so you can't see it. If there is a dull glow inside, the heater is on. The only part of the heater that matters is inside where it cannot be seen anyway.

The power tubes run on 6VAC and so does the phase splitter. The three preamp tubes run on DC heater voltage. If one of them lights up, that means the DC voltage is being created, and then I'd have to think the sockets were loose or something to kill a couple of them. The three are wired in parallel. I think there is a pair of wires twisted running tube to tube with that voltage. Or just pull a tube from its socket and probe with your meter. There is voltage between pins 9 and 4/5 or there is not. If it is actually the three DC heater tubes dark, then the rectifier bridge itself is where I'd look.

Meanwhile I would be looking for missing B+ voltages. Is there several hundred volts on the plate and screen pins of the power tubes?

For reference, in my shop, labor would likely be in the $60-75 range. PArts could be anything from nothing to a bad transformer somewhere. If the problem really is dark tubes, that is nothing. If it is something else, usually it is no big deal to diagnose. Unlikely, but if it were a transformer, those run I think in the $75-100 range. I give free estimates if I have to estimate, but most shops charge for diagnosis, with the estimate fee going toward repair if accepted.

[DiezelAmpPlayer]

Don't believe everything you hear or see on th einternet. These amps may have more failures than others in certain areas, but that doesn't mean they ALL drop dead once a week.

First, turn off the room lights and look at those tubes in the dark. The heater on some tubes does not stick out far so you can't see it. If there is a dull glow inside, the heater is on. The only part of the heater that matters is inside where it cannot be seen anyway.

The power tubes run on 6VAC and so does the phase splitter. The three preamp tubes run on DC heater voltage. If one of them lights up, that means the DC voltage is being created, and then I'd have to think the sockets were loose or something to kill a couple of them. The three are wired in parallel. I think there is a pair of wires twisted running tube to tube with that voltage. Or just pull a tube from its socket and probe with your meter. There is voltage between pins 9 and 4/5 or there is not. If it is actually the three DC heater tubes dark, then the rectifier bridge itself is where I'd look.

Meanwhile I would be looking for missing B+ voltages. Is there several hundred volts on the plate and screen pins of the power tubes?

For reference, in my shop, labor would likely be in the $60-75 range. PArts could be anything from nothing to a bad transformer somewhere. If the problem really is dark tubes, that is nothing. If it is something else, usually it is no big deal to diagnose. Unlikely, but if it were a transformer, those run I think in the $75-100 range. I give free estimates if I have to estimate, but most shops charge for diagnosis, with the estimate fee going toward repair if accepted.

Hey thanks for the reply man.

I just read another thread around here were it was asked if the board itself underneath the pre-amp tubes socket, if it was dark or a different color. Well, I remember this from the last time I pulled the thing apart and mine defenitely is darker yellow or light brown around the area of the socket for the tubes in question. Actually, those 3 tubes that don't light up are all darker color underneath so that might tell you something..?? I'm just trying to make it as clear as possible to describe.

I'll check all the above you suggested and see if what I can come up with. If it's that much to repair then it's worth it to me.

Thanks again man.

[Jay D]

Marshall JCM 2000 DSL 401

Hello:

PLEASE - PROCEED WITH CAUTION AS VACUUM TUBE AMPS, AND WORKING WITH HIGH PLATE VOLTAGES.

I am in the process of repairing a Marshall JCM 2000, and the same problem(s) has happen. Check the bridge rectifier solder connections, and the two large filter capacitors, C68 and C73 for bad solder joints. Over time I have found that the heating and cooling of the leads can cause the solder joints between the component lead and the solder pad to crack and become intermittent.
I also had to re-solder the CON1 and CON2 connector solder joints, as I was also loosing the channel switching and LED's.
The amp now powers up, all three pre-amp tubes light and once the stand-by switch is on, the amp produces sound, but fades away and goes silent.The two power supply filter capacitors 22uF, 450 VDC, are intermittent solder joints, and the second 22uF,450VDC cap is bas and needs replacing.
Good luck,

Jay D