Marshall valve assignments

[Antag]

Hi All,  quick question about the JCM900 SL-X I recently acquired.

Looking at the valves in this picture left to right:



I'm guessing that V1 & 2 are gain valves, & V4 is the PI but what about v3?  Do Marshalls have valve-driven FX loops?  or another gain stage?

[Twinfan]

3 gain stages and a PI I reckon.....

[Will]

I had the 2100 std, I think the SL - X was Superlead Extended, with the diode clipping replaced by extra valve clipping

[hunter]

maybe the loop?

Does the amp still work if you pull V3?

[FELINEGUITARS]

I had the 2100 std, I think the SL - X was Superlead Extended, with the diode clipping replaced by extra valve clipping

That is correct
The JCM900 came in for some criticism that they had a diode clipping stage in the distortion chain - so Marshall came out with the SLX- I think the first two valves are 3 or 4 cascaded gain stages- v3 is the tonestack and V4 is the PI

Maybe someone could affirm or clarify this?

[Antag]

Can anyone make sense of this schematic?.  Damned if I'm any the wiser...  :?  :lol:

[HTH AMPS]

V1-3 are all gain stages (ish, but lets keep this simple).  The tonestack is fed in the usual Marshall way from a dc-coupled cathode follower from V3.  Then you have the opamp-driven effects loop, then V4 is the PI.  So you have four gain stages.