Older 11 knob DSL100h red plating help please

Leonard Neemoil

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Hi folks.

TLDR; got a used dsl 100 H. Cleaned all jacks and tube sockets. Cranked great for about 2 weeks. 2 days ago it red plated on the left 2 tubes. Cleaned the output jacks again and cycled it on for 30 minutes and off to cool 3 times with no problems. Then cranked it for a few hours with no problems.

Do I just need to do the output ground mod to stop possible future red plating/circuit board meltdown?
If interested in more details please read below. Thanks.

Ok, actual post below;

Two weeks ago I bought a used dsl 100 H.

I knew about the runaway bias problem but took a chance anyway. The thing is MINT! I couldn't believe it.

Removed the chassis and cleaned all the jacks inside and out along with all of the tube sockets. Used residue free contact cleaner and ran a plug/tube through the sockets while spraying. Let it dry and fired it up.

Amp sounded phenomenal and phenomenally loud. Loved it.

Been cranking loud for hours a day nearly every day for 2 weeks.

So 2 nights ago I warmed up the amp. Usually about 10 minutes.

Flipped the standby switch (usually let everything warm up an additional 10 minutes). So I figure I'll play on my phone for 10 minutes.

About 1 minute later I hear a pop (not really loud though). I looked up and saw the left 2 tubes we red plating. Shut amp off. Tubes didn't get hot enough to blacken the writing on them. Stock Marshall tubes or replacements from Marshall.

Chassis has been out of the shell since arrival waiting for new tubes, bias, and ground wire mod for the speaker outputs.

So once cool, I looked underneath for any burnt components or popped fuses.

Nothing. All looks good.

So due to a possibile bad connection with the 8ohm jack, I cleaned the output jacks again like when it arrived at my house.

Let it dry, warm it up, and flip standby.

Left it off of standby for half an hour with NO red plating. Keep in mind, it had only been off of standby for about 1 minute last time when it started to red plate on the left 2 tubes.

The tube glow looks even in color between them all, tube temp feels even amongst the bunch when I put my hand an inch above them, and it seems to sound fine.

Did that 2 more times that night after letting it cool in between. Then I cranked the snot out of it for a couple hours.

All good.

Could it just be the stupid dsl ground problem with the output jacks that I'm soon to fix?

Is that the only reason these things meltdown?

This is the older dsl100 h version with only 11 knobs and 3 output jacks, not the newer dsl100h R with midi and all that.

Those of you who made it through this novel of a post please share your opinions/experiences.

Can I just do the output ground mod and be set?

Thanks for any help.

Have a great night.

Cheers!
 
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Leonard Neemoil

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what was the bias reading?

Haven't checked it yet. Had to order a multimeter that read millivolts. Received it a few days ago so I guess I should check.

It sounded a little low if anything, definitely not saturated, and still sounds the same.
 

Dogs of Doom

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There's a couple resistors that feed the bias, that wreak havoc on the JCM2000 series amp's.

IMO, they were underspec'd, because they are always going out.

There's a few threads on here, about the TSL100, where ampmadscientist gives some testing you can do. You'll want to do them. You pull the power tubes, so as to avoid any damage to anything...
 

Leonard Neemoil

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There's a couple resistors that feed the bias, that wreak havoc on the JCM2000 series amp's.

IMO, they were underspec'd, because they are always going out.

There's a few threads on here, about the TSL100, where ampmadscientist gives some testing you can do. You'll want to do them. You pull the power tubes, so as to avoid any damage to anything...

Thanks for the advice. This amp is just a plain dsl100h, no jcm 2000 in the model name if that matters. IDK.

Also, should I have put this in the workbench forum? If so can you or some other mod move it please? Thanks.
 
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Leonard Neemoil

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what was the bias reading?
Ok finally found time to check the bias.

Was actually higher than I would have guessed according to the sound.

So I got 90 on the right side.

84 on the left side, this side was the one that was red plating.

Adjusted them to both be around 84-85.

Wish I had received the multimeter sooner so I could've checked the bias before the partial meltdown.
 

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