Occasional sharp crackle from DSL. Time to get spare EL34’s?

noisepolluter · August 2023

Bought new around April so annoyingly valves probably out of warranty by now. I have some spare 12ax7’s but not EL34’s, probably sensible in any case to have a matched spare pair of bog standard JJ’s - if it turns out to be one of the 12ax7’s e.g. phase inverter at least the 34’s will be useful eventually.

Still annoying though. I imagine there’s probably virtually no grading with stock valves for most non-boutique amp makers

ICBM · August 2023

Thankfully you said bought new in April

... my first thought when you said DSL was one of the notorious arcing problems that afflicted the original UK-made JCM2000 ones.

If it is valve-related, a sharp crackle is most likely to be an EL34, but it could also be V3, which is the cathode-follower in the preamp. It's less likely to be any of the other preamp valves (although still possible).

noisepolluter · August 2023

Thanks @ICBM - do Marshall have the DSL preamp valves in an odd layout E.g. back to front in terms of usual numbering?

ICBM · August 2023

No, V1 should be at the input jack end and V4 furthest from it.

I only have the schematic for the 40 and 100, but I think the 20 is the same.

noisepolluter · August 2023

Thanks, it’s the 40. I will say that it was biased too hot out of the box (41/42mV and Marshall said it should be 35 per side), but I corrected it fairly quickly and it’s not been thrashed.

Oh well - I had a 6V6 crap out after a couple of weeks in a new Princeton a couple of years ago, I pretty much expect it.

noisepolluter · August 2023

Actually now I think about it there’s been a soft burbling background noise pretty much constantly which seems unaffected by master/volumes etc.

Could that also be the cathode follower?

ICBM · August 2023

noisepolluter said:

Actually now I think about it there’s been a soft burbling background noise pretty much constantly which seems unaffected by master/volumes etc.

Could that also be the cathode follower?

Probably not, the cathode follower is before the master volumes.

noisepolluter · August 2023

I swapped out the stock 12ax7’s in both V3 and V4 with fresh JJ’s. No further crackles at the moment, and the low-level rustling seems much reduced. I suppose I should have just done it one at a time as it was unlikely to be both valves playing up. Oh well.

Have ordered a spare set of EL34’s as well, as they’ll be needed sooner or later.

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Occasional sharp crackle from DSL. Time to get spare EL34’s?

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