Marshall JCM2000, DSL50 of 2002

Owner rarely uses anything other than green clean ch. It dropped in output so instead of his usual 2.5 on the dial , needed 8. Found the usual sort of problems on input socket and output speaker current switching ground contact and a switch but nothing that will bring the gain up in clean, from the output it was giving whan I received it. All valves test good and balanced, same set for 6 years of use. Some test results with 0.05V rms 400Hz in (600R SG) with all pots at mid and all switches out (except the clean/crunch etc where necessary) and grids of V1 and V2 ........... Clean ........... Crunch o/p 8R 0.5V 7V send socket 0.01 0.16V V1(p2) 0 0 (comes up to 0.2V on red and 0.4V red +ultra gain) V1(p7) 0.05 , 0.05 V2(p2) 0.046 , 0.74 V2(p7) 0.01 , 0.18V

Anyone see anything awry there, seems ballpark to me? I suspect a problem has occured in his Marshall 1936 cab , that I've not seen. 2x 16R AFAIK. He's using 8R on amp output and cab input. If problem with input diverter contacts or wiring or one speaker and now running one speaker only and so 16R from 8R then a 1/3 constant volume drop makes sense. Any test an owner can do without lending him a meter?

1.2V or 1.5V battery contacting the speaker lead jack, could you tell whether 2 sound sources under the grill cloth , by listening? I would push a thin rod through the grill to touch the cones , in turn, but not something I could advise someone else trying

It is usually very easy to determine, even for a drummer, whether there is sound coming from both speakers in a 2 x 12. You just have to put your ear to the grille cloth.

Gareth.

Could he also be having a problem with whatever instrument he's using not putting out enough signal? I am thinking of something like a guitar pickup switch screwing up.

Matt Roberds

I asked if he'd tried his guitar and lead on another amp+speaker, and no. Would not failed wiring/pickup show itself as a change of sound issue? as well as level, especially with someone using the same guitar for more than 6 years

That is an interesting series of Marshalls.

Yes, I think it's more likely that it would sound different - and "different" means something other than "not as loud". But I figured I would bring it up as a possibility, since the amp seems to be working OK.

Matt Roberds