Marshall JCM2000, DSL50 of 2002

[N_Cook]

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

 

N_Cook <diverse@tcp.co.uk> wrote:

I suspect a problem has occured in his Marshall 1936 cab , that I've
not seen.

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

 

[Gareth Magennis]

"N_Cook" wrote in message news:lo9ckt$2a7$1@dont-email.me...

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.

 

[N_Cook]

On 24/06/2014 01:23, mroberds@att.net wrote:

N_Cook <diverse@tcp.co.uk> wrote:
I suspect a problem has occured in his Marshall 1936 cab , that I've
not seen.

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

 

[dave]

On 06/23/2014 01:32 PM, Gareth Magennis wrote:

"N_Cook" wrote in message news:lo9ckt$2a7$1@dont-email.me...

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.

That is an interesting series of Marshalls.

http://music-electronics-forum.com/t12900/

http://www.hullerum.de/Marshall/TSL122repair.html

 

N_Cook <diverse@tcp.co.uk> wrote:

On 24/06/2014 01:23, mroberds@att.net wrote:
N_Cook <diverse@tcp.co.uk> wrote:
I suspect a problem has occured in his Marshall 1936 cab , that I've
not seen.

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.

Would not failed wiring/pickup show itself as a change of sound
issue?

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