'72 Marshall Lead 50w in Royal Purple

1972 Marshall Lead 50w in Royal Purple

This is my 1972 Marshall Lead. It's a 50 watt PTP. Man, it is sweet. It has Mullard 12AX7's and EL34's.

Sound:
God, it sounds awesome! It has much more harmonic content and sustain than my '76 (which I love). I think it's due to the Mullard tubes. I'll try to make some clips soon... This amp sounds so open and full!

It's much brighter purple than shows up in the photos. I'm not much of a photographer.

English style mains selector and bulgin plug.

Board: Notice the yellow chicklet caps that appear in very late '71 and all of '72. There were originally no grid resistors.

Split cathode on V1 .68uf/2K7 and 320uf/820;
.0022 1st stage bright coupling cap - normal for Lead model;
470k mixer resistors;
no bright cap (was 0.005uF originally and was way too bright);
500pf mixer bypass cap;
no bypass cap on V2A cathode (probably because of 100k NFB on 4 ohm tap);
33k/500pf tone stack combo, normal for Lead model;
100K NFB resistor on 4 ohm tap (lots of power amp gain here - specific to '72);
.022 output coupling caps for Lead model;
220k bias splitter resistors;
.1 cap on the presence control;

Tube DC Operating Voltages

Pin #	1	2	3	4	5	6	7	8	9
V1 ECC83	125	--	0.78	Htr	Htr	178	--	165	Htr
V2 ECC83	145	--	1.03	Htr	Htr	260	147	148	Htr
V3 ECC83	203	--	40.4	Htr	Htr	173	--	40.4	Htr
V4 EL34	--	Htr	422	420	-40	--	Htr	0
V5 EL34	--	Htr	422	420	-40	--	Htr	0

Power Supply Voltages

Plate Voltage	422v
Voltage between two 10k's	345v
V3 Voltage	285v
V2 Voltage	258v
V1 Voltage	240v

Close up of the left side:

Close up of the right side:

V1b to V2a Lead Channel Coupling Cap 0.002uF MetalMite!!!

Mullard 12AX7:

Mullard EL34:

Halfstack:

Doublestack (note the ceiling fan cords, it's very close to the ceiling):

PPIV Master Volume Mod

I added a post-phase inverter (PPIV) master volume (MV) mod to this head to help reduce the crushing volume levels. The mod that I used is called the RICH mod (named for the creator) by the users of the Les Paul Amplifiers Forum. Here are few pics of the mod: