Reference Archive
1972 Marshall 1959 Super Lead
This was a fun one to work on. When it came into my possession it was unfortunately missing most of the original coupling capacitors, and some other components were swapped as well.
I started by repopulating the board with some mustard caps from my stash, but this one would have likely had the yellow Philips chicklet style caps, as indicated by two original ones remaining in the tone stack. I kept the preamp stock, including a bypass cap on the V2 cathode. For this I didn’t have another 680n, but I did have a 560n, which is close enough. I A/B’d the two values and it doesn’t make much of a difference, so I used the 560n to keep the parts period-correct. Normally I don’t use a bypass cap on V2, but this bad boy has a B+ of 508V, so it could use a little extra gain to not feel stiff.
The filter capacitors were some nice LCRs from ’92, and while they were all functioning fine, I opted to install fresh F&T filter capacitors—mainly because the previous wiring job was trash and I wanted to clean it up.
The output selector was in rough shape, and the text was gone on the selector as well, so I replaced this with a new heavy-duty impedance selector switch.
During bench testing, the output tubes that were in it were red-plating slightly. They were Groove Tubes EL34Ms, which are good tubes, but the plates glowed even when biased conservatively. This prompted me to up the screen grid resistors to 2.2K since this amp has such a high plate and screen voltage. I then installed an unbranded set of Chinese EL34s with heavy-duty plates, and they were running flawlessly with the amp cranked at full volume.
Other key circuit notes
Someone had installed a 47pF bright cap across the normal channel volume control. This really didn’t have much of an effect, so it was left in place.
- 2.2n bright channel coupling cap
- 4700pF bright cap across bright channel volume control
- 100K NFB on 4 ohm tap
- 22n PI coupling caps
- 100n presence cap on 5K pot, no 4.7K resistor present
- Polarity switch defeated. Death cap left in amp but no longer connected. No reason to have it when using modern 3 prong plugs
- Added dedicated ground lug for mains ground
Normally I don’t like the small bright channel coupling cap or the 100n presence cap, but this amp did not sound overly bright and still felt nice and thick when pushed. With a 22n bright channel coupling cap, I tend to not roll the volume all the way up, so the bright cap helps to limit bass going into the next stage. With the smaller coupling cap, you can turn the channel volume control up all the way without the tone sounding bloated.
Hear the amp
For this clip the amp was played through a ’74 Marshall 1960 full stack with original Celestion G12M 75Hz speakers, mic’d with a Soyuz V1 and a Beyerdynamic M160.
Schematic and voltages
There are so many variations of Super Lead circuits out there, I thought it would be cool to draw up the schematic and include voltage measurements for reference. Check it out and feel free to share.
Download the full high-resolution PDF schematic© Purgasound 2026 · www.purgasound.com