Burnt up DSL100HR.. Replace board or build vintage spec clone?

[CHall1525]

Quick info.. Just joined, first post. I am capable, but not all knowing, inside a tube amp. I'm still learning a lot of the terms and forget them pretty quickly so ignore my ignorance. I have built a mojotone 5e3 tweed deluxe clone with success, and troubleshot and changed components in a couple vintage Fenders I own. This includes a couple of Bassmans, a vibrolux reverb, and a champ. This is my first Marshall to tinker with.

What it is... I purchased a busted (fried board) DSL100H with reverb but no "R". It is the version with the chassis mounted power tubes. All the replacement boards I have found online are for a different version with pcb mounted power tubes. My board is stamped DSL 100-60-00. I have contacted Marshall service but don't plan on much help as I am not the original owner, but maybe they could sell me the board. If anyone has a source for my board I am all ears.

Another option... Build a vintage spec turret board of a classic Marshall using the chassis, transformers, cab, etc of the dsl. What would be the most correct/best sounding circuit to fit the transformers from the DSL? (assuming they are good, I have to figure that out also). Any major roadblocks I may not be thinking of trying to go this route?

Thanks in advance for any help or advice.

 

[Chris-in-LA]

You need to find out if the transformers are good first. I would be tempted to build something classic if they were good. Can you post a picture of what you have to work with?

 

[Gene Ballzz]

@CHall1525
Even if the transformers are good, one difficulty will likely be finding out what the specs for them are! Sure, you can teast for voltages, turns ratio, etc, but that won't give us the mA ratings/capabilities. Given the tube complement and claimed wattage, we can certainly make some "assumptions" but you know the old adage: "To assume makes an a$$ out of u and me!"

And Oh Yeah, To The Forum!
Gene

 

[XTRXTR]

2203 with a FX loop, if the iron is good it should be rated for a 100 watt anything named Marshall, I just looked at the schematic.

 

[Chris-in-LA]

2203 with a FX loop, if the iron is good it should be rated for a 100 watt anything named Marshall, I just looked at the schematic.

Are you suggesting that OP use the 100 watt DSL iron to build a 2203 with an effects loop?

 

[XTRXTR]

Yes I am saying 2203 with additional tube for FX loop. The schematic shows heaters for 4 pentodes and 4 triodes on a JCM2000 DSL 100. I followed the schem and verified that. The JCM 2000 has an Fx loop or a reverb tube. The Iron is made for it already so why not? Plus he already has the layout on the chassis. Build a P2P version of a 2203 with a fx loop.

 

[Gunner64]

Are we talking a JCM2000 DSL100? And what do you mean by fried? The bias drift issue or is it actually physically damaged?

If it's just the 2kdsl drift issue I would install the Dr. Tube stable bias kit, new bias pots, and do the ground fix on the output jacks. That is if the transformers are ok.

 

[CHall1525]

Not a JCM 2000. Just has DSL100H on the front.

It roasted around v2 and v3.

 

[paul-e-mann]

Yes I am saying 2203 with additional tube for FX loop. The schematic shows heaters for 4 pentodes and 4 triodes on a JCM2000 DSL 100. I followed the schem and verified that. The JCM 2000 has an Fx loop or a reverb tube. The Iron is made for it already so why not? Plus he already has the layout on the chassis. Build a P2P version of a 2203 with a fx loop.

This is exactly what I was thinking

 

[Gunner64]

Not a JCM 2000. Just has DSL100H on the front.

It roasted around v2 and v3.

Holy crap! Roasted is the right word. Thats junk for sure.

 

[geddy]

If it were me, I'd want to try and work out why the PEC failed. That could guide your decision. What might have failed that might have taken out the board? You may be able to fix that by using discrete wiring and replacing components. Difficult to tell from pics.

Which country are you in? Marshall factory are very good for support in the uk

 

[Gunner64]

I'd get the correct new board for the amp, that is if it would be financially feasable.

Idk what you have in it, or what a new board would cost but If it would cost more to fix than its worth I would explore other options. Imo repairing that board would be challenging.

 

[CHall1525]

Not trying to repair this board really, and the replacements I have seen are in the $250 range, which for what I paid would still be under used prices if a DSL, but I still haven’t found the exact one I need. Still holding out to see what Marshall Service tells me.

Anyone got a good source to show me how to check out the transformers for proper voltages, problems etc.? haven’t dug in too deep yet.

 

[JP2036]

Considering a new Vietnam Marshall is $600 bucks how much money do you plan on spending ?

 

[CHall1525]

Would like to keep the repair in the $250 range or under. Would put me around $500 total.

 

[neikeel]

YOu can test the PT by disconnecting all the secondaries and measuring the (albeit unloaded) voltages to see if they are in spec.

For the OT you will need a variac and a calculator. Disconnect the mains and remove the output tubes and apply 100v to the ends of the primary wires Pin 3 of first and last output tubes

Insert the 1/4 inch phono plug into the speaker output jack.

Measure the AC voltage across the secondary tap. 4, 8 or 16 it doesn't matter which. (See drawing 2) I like to check each one.
Make sure the impedance selector is set to the tap that you want to check.

Divide the input voltage by the output voltage. This gives you the voltage (turns) ratio.
The amount of turns on the primary to 1 turn on the secondary.

Take the turns ratio and square it (VTR x VTR). This gives you the impedance ratio.

Take the impedance ratio and times it by the secondary tap rating 4, 8 or 16. You now know the ratio of the OT and whether it is functioning as it should. If you are feeling brave crank you variac higher (mine only goes to 250v) to check you don't get shorts or funky readings.

I'd expect 1.7k or so for a 100w running EL34s.

I agree with Gunner, try to get a new board once you've excluded other faults.

Failing that a 2203 with variable NFB, resonance mod and dual MVs will help fill up some of your front panel control holes!

 

[CHall1525]

Response from Marshall. AKA I’m on my own.

So it’s looking like a conversion is going to be my option.

@neikeel Thanks for that info, I will start on the trannies and verify they are operational and go from there.

 

[JP2036]

There is no single worse problem for a guitar player than a sick amp.
Its the worse.
I wish you well but amps are like women : there's millions of them don't get all jacked up on just one.
Seriously there are millions of great amps that need good homes.
Happy hunting sir !

 

[XTRXTR]

Uncle Doug has a good video on testing an OT.
@neikeel Information is great for the OP situation where the Iron is already installed and needs to be tested for damage. To protect yourself and the OT from heavy current draw (in the case you have a short in any of the OT winding or you accidentally touch an open lead and close the circuit) I would add a large light bulb current limiter between the variac and the OT under test. In case any new DIY'r is wondering the 100v needs to be 100 VAC, you can't test primary to secondary voltages using DC.

Regarding the testing of the OT perhaps before you add any voltage you should use a DMM and look for an DC open circuit on both the primary and secondary. An open circuit would mean you don't need to test at all and unfortunately a replacement would be required. I think I would look for an open, a short and DC resistance...you know play with the DMM dials.

To be clear look for an open on the Primary with tubes pulled between pin 3 of the far left power tube socket to pin 3 of the far right power tube socket. These should be directly connected to the OT with brown and blue wires. But, I don't have that amp in front of me and it is possible that a terrible design going through a connector to another board to another connector to the OT was employed.

On the Secondary just use a 1/4" open cable-less plug and measure the tip to sleeve blades inside the cover while it is plugged into the speaker output jack and switch the impedance selector from 4. 8, and 16 Ohm while looking for an open. You could use this plug to test the AC voltage afterward per neikeel suggestion once applied.

 

[Gene Ballzz]

YOu can test the PT by disconnecting all the secondaries and measuring the (albeit unloaded) voltages to see if they are in spec.

For the OT you will need a variac and a calculator. Disconnect the mains and remove the output tubes and apply 100v to the ends of the primary wires Pin 3 of first and last output tubes

Insert the 1/4 inch phono plug into the speaker output jack.

Measure the AC voltage across the secondary tap. 4, 8 or 16 it doesn't matter which. (See drawing 2) I like to check each one.
Make sure the impedance selector is set to the tap that you want to check.

Divide the input voltage by the output voltage. This gives you the voltage (turns) ratio.
The amount of turns on the primary to 1 turn on the secondary.

Take the turns ratio and square it (VTR x VTR). This gives you the impedance ratio.

Take the impedance ratio and times it by the secondary tap rating 4, 8 or 16. You now know the ratio of the OT and whether it is functioning as it should. If you are feeling brave crank you variac higher (mine only goes to 250v) to check you don't get shorts or funky readings.

I'd expect 1.7k or so for a 100w running EL34s.

I agree with Gunner, try to get a new board once you've excluded other faults.

Failing that a 2203 with variable NFB, resonance mod and dual MVs will help fill up some of your front panel control holes!

#1> I don't see any "drawing 2" or any other drawings. Did you space out on sharing them?
#2> Idon't believe the OP's @CHall1525 amp has any Master Volumes and certainly not two of the, as on the newer DSL100HR.
#3> It's interesting that the "roasting" occurred in the preamp section? IIRC, these amps my have DC heaters for the first or more preamp tubes. Something went very terribly wrong here! I would not suspect the transformers to be the culprits here, but one or both may well be the victims of whatever happened. I'm kinda suspecting beverage spillage related!

Definitely a good idea to asses what is salvageable, before spending any $$$ on it!

Just My & Likely Worth Much Less!
Gene