DSL100HR Red Plating!
- Thread starter Cadorman
- Start date
Amp Mad Scientist
Ambassador of Heresy
Some of those tubes which are run in DSL seem to develop a runaway thermal problem.
The tube starts out normal, but then as it heats up - it draws more and more current till it overheats and turns red.
But the problem stays with the tube and doesn't appear to be caused by the amp itself. (not yet anyway)
When the tube is changed with a new one, the problems stop and all seems normal again.
But if these failures are caused by the amp, we don't know why yet.
It could possibly have something to do with insulation breakdown on the circuit board, allowing B+ voltage from the plate (pin 3) bleeds into the filament (pin 2).
And after this goes on for some time, the tube develops the runaway thermal problem...
[the filament power connectors from the power transformer on the circuit board start to overheat and burn}
Although UN-confirmed this is the only insulation issue that I have identified as plausible so far.
So you see?
There is more problems on this board than "just" bias drift.
There are actually a number of issues where insulation is breaking down.
Plate to filament - maybe.
Destruction of DC filament supply for the preamp - maybe. Caused by B+ bleeding into the filament tracks.
(I suspect that something is going on with this).
The circuit boards are made of sub-standard low grade fiberglass - the insulation fails.
The circuit tracks on the board are too close together causing insulation failure.
Amp Mad Scientist
Ambassador of Heresy
You can run 2 tubes at a time, not 4. (I think but I don't have the schematic)
Put the 2 tubes in the middle 2 sockets.
Then by process of elimination, you can swap the tubes out and locate which single tube is causing the problem.
I have been doing this with DSL 50 / 100. But I don't know if DSL 100 H is wired the same way (probably is).
Amp Mad Scientist
Ambassador of Heresy
That's good.
Every test you report will help other people fix DSLs.
Once there is enough info accumulated, it will help solve other amplifiers (it helps a lot).
I’d take it out back and shoot it! Ok, with a BB gun.
chilipeppermaniac
Ambassador of Decibels
This is what I have found to be the case too. As I began learning amps, I got nice teachings from Bastard, 67, Ampmad, Sysco, DonP, Ivan, Smitty, SGJOhn...
but also across the web and from reading amp issues from other members in here like RobertH's DSL's
Big Bastard Don is the first person to point out evidence of redplate issue on one amp I bought a few years back. I suspect this one was not the fault of the board or traces etc, but as we found, numerous bad tubes and some other bad hands in the amp in the past.
All this talk about pins and heaters and filaments and getters etc all used to me mumbo jumbo to me, but began to make sense during hands on and book learnin for me. I just have to keep at it often so it becomes 2nd nature.
chilipeppermaniac
Ambassador of Decibels
Get the thing sorted out with your most reliable tubes, If the factory tubes are available, try those first. If you get it sorted and working reliably, return it under warranty if you still can.
Buy a different amp with better circuit boards etc.
OP
Cadorman
Ambassador of the Catocaster
You guys are killing me. It was fixed yesterday. I just stuck the known wandering pair in my 50 watt 1987 with my VHT meter hooked up and one channel went to 44 mv and the other went to 100! Then I tapped on the top of the tube and it dropped to 80. Then 60 and finally 40. Swapped positions and the condition followed along. I could keep tapping and make it go up as well. Pulled them out and the bad one rattled like a blown incandescent light bulb. And it still works, just not how you want it to.
chilipeppermaniac
Ambassador of Decibels
OK Lefty, good news. I was just tryin to get you a free amp.
OK, now take it out back and shoot it !
Amp Mad Scientist
Ambassador of Heresy
DSLs are cursed by Voodoo Priests, true.
But people keep playing 'em.
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eSGEe
Ferengi Ambassador of Trade
extremely sad on an amp that new and of that "price caliber" ........
Id expect such in a Behringer or Bugera 15 watt hybrid
not a Marshall 100 watt head
Amp Mad Scientist
Ambassador of Heresy
Tubes can get damaged from shipping and you can sort of expect that once in a while...extremely sad on an amp that new and of that "price caliber" ........
Id expect such in a Behringer or Bugera 15 watt hybrid
not a Marshall 100 watt head
Different amps too with tubes base down, and tubes base up.
The problem may have been noticed if the tube was mounted base up instead of down etc...position related vibration related failures.
A bad tube can show up anywhere at anytime , it not like a brand new engine in your truck, ever replaced a light bulb and with in a week have to replace it again ??extremely sad on an amp that new and of that "price caliber" ........
Id expect such in a Behringer or Bugera 15 watt hybrid
not a Marshall 100 watt head
I have.
One of my Dsl40c’s has eaten 3 power tubes in 5 years, while the other one is still happy with the ones it came with..
Chris I am glad ya got your amp back on track and running healthy.
Cheers
90 days or 90 songs, 3 months or a Minor 3rd, whichever comes first.
I know for a fact that tubes are excluded from Marshall's warranty protocols, but not sure about other amp makers.
eSGEe
Ferengi Ambassador of Trade
I had a DSL40c that every time I played it one of our pets passed away the same day .......... I traded it off
Speaking of which anyone wanna buy a Marshall origin 20h ???????? No really -- like new w/ marshal pedal --- PM me
-- probably to costly to ship though-- buy a new one for about the same .........
Amp Mad Scientist
Ambassador of Heresy
Well, the circuit board can have a defect which kills the tubes.
And so when this happens we keep a watch for the defect.
We want to know if it "is" just a bad tube, or if the amp is killing the tubes one after another.
Some DSL models have had numerous problems.
But the funny part is, no matter how many times these DSLs screw up, people keep fixing them and playing them.
I gigged a pair of DSL40C (a 2014 and a 2015) for 2 years, 5 nights a week and most Saturdays, plus used them daily in the studio, leaving them on for up to 8 hours at a time, and never had a problem with either one other than periodic tube replacement.
Seems like the 'Bedroom Players' may subject them to rougher handling???
I just don't have the reliability problems that I hear so much about...
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Amp Mad Scientist
Ambassador of Heresy
It's not every amp they made. I have seen only a couple DSL40c have a circuit board problem.
It was DSL 40CR that people had a time with, it was a microprocessor firmware issue. And there was a problem with glue used on the board that shorted out the circuit tracks....
There was DSL TSL 50 100 circuit board problems, and the 16 ohm jack should be replaced because the switch contact fries out.
And there is an issue with the bias adjust pots failing prematurely and that also caused red plating.
In the earlier amps there was a speaker jack fail problem, but I think they stopped using those jacks.
It not like they all fail, it's just some of them.
Some people have more luck than others.
But I think it's more of an issue with many techs just don't understand the failure causes.
Some techs are just fed up with trying to fix the issues.
And I can understand why. Thes amps were not the best designed or easiest to work on that I've ever seen.