Marshall DSL40C failed mid-gig last night

longjaw

Towards the end of the first set of my gig last night my Marshall combo packed in. 

It was making a God-awful loud buzzing sound intermittently which I thought may be due to a dodgy lead or bad FX pedal lead connection.

I gradually removed my pedals between songs, in case that was the issue -  until the guitar was plugged directly into the amp. I then tried a different guitar and it still persisted.

The noise got worse and worse as the night went on until it was buzzing all the time and that was the end of it!

I've tried the amp again today and it's doing exactly the same thing.

Here's a video of it happening (the problem occurs around 20 seconds in) : 

Any techs able to diagnose the problem?

I've had the amp from new and used it extensively over the last couple of years, so could it be a failed valve?

Any help much appreciated!
Cheers

Voxman

Sounds like a duff tube, probably a preamp tube?

longjaw

It would be great if it is! Anyone else think it's failed pre-amp tube?

ICBM

I can’t listen to the video at the moment but it is most likely a failed valve - preamp or power amp, I can't say.

First, remove one of the EL34s and test the amp - if the problem has stopped, the fault is in the one you've taken out. If not, replace it and remove the other one, and repeat. It's safe to operate a fixed-bias amp temporarily with one valve missing, although it won't sound good at higher volumes with a guitar through it.

If it's not either of the power valves, replace the preamp valves one at a time with a known good spare.

If it is a power valve you should replace both of them, but keep the non-faulty one as a spare, it may be useful...

longjaw

Cheers bud, I'll give it a try.

longjaw

Well that was a thoroughly frustrating hour.

Removed an EL34 played for 10 minutes without any problems so obviously thought that must be the culprit.

I thought I'd put the valve back in, just to confirm so I did and played for half an hour with no problems at all!

I suppose I'lI have to try again tomorrow night.

ICBM

It could possibly have been a bad contact between that valve and its socket which you’ve accidentally fixed by taking it in and out... but it’s usually not as easy as that, and it’s some annoying intermittent problem waiting for the worst possible time to reappear .

longjaw

Ha, sods law innit!?!

Forgot to mention I also tried putting the amp on maximum volume with nothing plugged in and tapping the valves - all seemed fine there.

Think I'll try leaving the amp powered up for half an hour or so tomorrow evening to get the valves cooking, then giving it another blast.

longjaw

Another hour wasted tonight, half an hour letting the amp warm up and another 30 minutes playing it at various gain levels and volumes with no problems.

Very infuriating!

longjaw

Update on this: I had the power valves replaced and re-biased by Root 2 Amp repairs, but the problem persisted.

Further investigations identified a problem with the PCB at the valve base for V2 - the amp tech re-soldered it.

I'll try it out when I'm next gigging near to home!

sgosden

I loved by DSL, but had no end of problems due to solder and the PCB, eventually sold it on pretty cheap.

annoyingly couldn't ever replicate the faults when trying to find them, only when at a practice or gig! (even if I had it at home running all day to warm it through)

riffpowers

Steve does good work, you must be from the north east are you??

longjaw

riffpowers said:

Steve does good work, you must be from the north east are you??

Yup - South Shields, Steve's workshop is literally a 5 minute walk!

longjaw

sgosden said:

I loved by DSL, but had no end of problems due to solder and the PCB, eventually sold it on pretty cheap.

annoyingly couldn't ever replicate the faults when trying to find them, only when at a practice or gig! (even if I had it at home running all day to warm it through)

I hope I don't have the same problems!

riffpowers

longjaw said:

riffpowers said:

Steve does good work, you must be from the north east are you??

Yup - South Shields, Steve's workshop is literally a 5 minute walk!

Canny, just the stairs to contend with then!!

sgosden

longjaw said:

sgosden said:

I loved by DSL, but had no end of problems due to solder and the PCB, eventually sold it on pretty cheap.

annoyingly couldn't ever replicate the faults when trying to find them, only when at a practice or gig! (even if I had it at home running all day to warm it through)

I hope I don't have the same problems!

mine was a 1999 DSL100 head, was on its second PCB when I got it 2009.

longjaw

From what I understand, the later EL34 Vietnamese version of the DSLs (mine) are more reliable and better designed than the earlier EL84 UK made ones.

ICBM

longjaw said:

From what I understand, the later EL34 Vietnamese version of the DSLs (mine) are more reliable and better designed than the earlier EL84 UK made ones.

Certainly from what I have - or more accurately, have not - seen, yes.

Slightly worrying that you’ve had solder joint issues with yours, but to be fair that’s not unknown with most amps.

gearaddict

I had a DSL50 head that I gigged for a couple of years and then it started cutting out randomly. I tried a few techs and in the end sent it to Marshall - it worked perfectly for all of them all the time but packed up every time I tried to gig it. I gave up in the end. Never did find the problem.

ICBM

gearaddict said:

I had a DSL50 head that I gigged for a couple of years and then it started cutting out randomly. I tried a few techs and in the end sent it to Marshall - it worked perfectly for all of them all the time but packed up every time I tried to gig it. I gave up in the end. Never did find the problem.

Did you use it with the standard Marshall 1960 4x12"? The mono/stereo/4/16-ohm switching panel on those is notorious for doing that. If you're unlucky it blows the output transformer as well...

If not, and you were using it at either 4 or 8 ohms, there's a switch in the 16-ohm jack on the amp which also does that with the same result. Very stupid design - and if you test the amp at 16 ohms, it doesn't show up.