DSL40C is having issues

[BrianTX]

Hey everyone,


New to the forum but not to the Marshall sound. I purchased a used DSL-40C and it worked well for a while. I changed the speaker to an Eminence 1250 and made the amp even better. I started having an issue about a month ago where the sound comes in and out. I'm gonna try to post a video below. Any amp techs out there that may have seen this issue before have any advice on where to start?? In the video, I am NOT manipulating the controls on the guitar; the sounds coming in and out is the amp.

 

[scozz]

Did you check to see if the tubes are seated properly?

Someone with more knowledge on this stuff will be here soon to help.


BTW, to The Marshall Forum!

 

[SkyMonkey]

Must assume you have tried new leads and a different guitar.
Deoxit all the connector jacks too, including the FX Loop.

Try and see if all the tubes are glowing (in a darkened room).
Commonly, problems are due to tubes.
If you have a spare ECC83 (preamp) that you know is good, you can swap out each preamp tube in turn to find a bad one.
Same with EL34 tubes for the power amp.

 

[jeffb]

In addition to the amp, check your wiring in the guitar. I've had a poorly soldered pickup lead or ground do that.

 

[What?]

On what has already been said, yea, verify first that your guitar and cable are ok (mostly likely they are, from what I'm hearing).

Using the effects loop can be helpful for finding which general area the problem might be in.

Plug the known good guitar and cable into the effects loop return and you should have a clean sound. If you are getting that same weak and distorted signal, the problem is in the power amp section or speaker. You can try another speaker to see if the problem is in the power amp or speaker. If swapping the speaker doesn't change anything, you have a problem in the power amp, which might be a bad tube or other issue. At this point I wouldn't just swap in a good tube in case there is an internal problem that could ruin the good tube. But you could at least check the bias to see if anything is crazy off. If the power section and speaker show to be ok, look at the preamp section.

If you have another amp on hand you can connect the effects loop send of the DSL to the input or return of the other amp using a known good cable. If the weak and distorted signal shows up, the problem is in the preamp. If the problem is in the preamp, first go through one at a time with a known good preamp tube and swap it into each position to see if the problem goes away, which you can also do without using the effects loop for troubleshooting. If the problem is in the preamp and tube swapping doesn't make it go away, you have other issues in the preamp, such as a bad jack or other component.

From what I have read, the DSL40's have had a number of common issues to do with how they are built, so you may be running into one of those.

 

[ken361]

those eat power tubes buy a set and test it real quick then have it biased

 

[Mitchell Pearrow]

Welcome to the forum
All great advice above me, Ken is correct on they like power tubes one of mine has had 2 sets since new 4 years now, and I try to play everyday so I don’t think that I’d be to far off, when I had a set going bad I used a pencil (chopstick) method to see it, and with the back off of the amp, they lit up with a tap, but I have never had a preamp tube make that type of noise.
Cheers to getting your amp back on track, they are killer little tone machine’s.


Mitch

 

[BrianTX]

Okay,

So I have changed the power tubes to Groove tubes and this did NOT remedy the situation. I did reseat the four preamp tubes while I had everything apart. I have new tubes on order and will post results. Thanks for all the info everyone, it's definitely the amp that's the problem, not any equipment.

 

[BrianTX]

Update:


I changed all tubes in the amp and I am still having issues with the sound coming in and out. It seems to be happening only in the Crunch channel, or that's where it's most noticeable. I am thinking that it may be the Clean/Crunch button. Every time I push it, it makes the same crackling sound as when the amp fades out.


New tubes = Problem still persists.....

 

[Wildeman]

Can you jumper the switch and see if it stops? If you're comfortable opening up an amp.

 

[Jimmy Bondy]

did you chanced the preamp tubes?

 

[BrianTX]

Yes, I changed the pre-amp tubes; now the amp has all new tubes, and is still acting up.

The switch is difficult to access as it is soldered directly onto a PCB.

The issue may also be the volume potentiometer on the Clean/Crunch channel. Today while fumbling with the amp, turning the volume knob produced a HUGE amount of static sound; the same awful static sound you get when you install StewMac pots in your Les Paul. I may reopen the amp and use some contact cleaner on all of the knobs and switches, which on this amp are all mounted to the same PCB. Not a bad design, just a PITA to repair.

In case anyone wants to know, I cannot tell any difference in playability or sound from re-tubing the amp. It plays and sounds the same, though the Eminence 1258 speaker definitely cleaned up the amp.