Metal Panel Superleads : why are they brighter and gainier ?

C

Cless357

Member
When I look at their schematics and compare to earlier Plexi amps, I don't see what could explain the brighter and gainier tone people describe.
Except for a higher filtering, a 2.7kOhms instead of 820 Ohms resistor in the first gain stage, and a missing 0.68µF cap in the second gain stage (which could thus give less gain !), the circuit are very similar.
 
Marshall was known to substitute whatever they had in stock for things they did not in those early years. Not every amp followed the schematic to a T.

Components also drift and over time that can cause both good and bad tonal changes as well as some reliability and fire risks on the extreme.

There’s also the hype aspect. Cant be explained but the metal panel eras more common and therefore more people will have owned and played them to have an opinion.

If you find a good sounding Marshall grab it. I kick myself in the ass for not getting a 1959 JCM800 4 holer transition amp at guitar center. With an SD1 it kicked ass. Went to go buy it the next week and it was gone.
 
Out of all my late 60’s / early 70’s 100W Marshalls, my ‘73 PTP Superlead is my absolute favorite.
It’s tight, aggressive and has lots of gain.
It doesn’t fall apart at all with everything on 10 & Volume 1 on 9 👍 (Hotplate @ -8dB)

I want to try out a Fryette PS-100 with my old amps, but I wish I could try before I buy.

I remember seeing very early 70’s Marshall Superleads (stock, in great shape) stacked on top of each other at a store called Tundra Music in Toronto, He must’ve had a dozen.
You could take your pick, $900 each.
I thought to myself, ‘he’s crazy, these amps will never sell at that price’!

Shoulda bought ‘em all😑
 
I remember when Steve Fryette had Edwards Marshall(The One)plexi on his bench he said it was closer to a 70s Marshall Superlead then a 68 Marshall plexi
 
Bright cap values make a huge difference, those values can differ from amp to amp, even within a single year. Cycle through the three way bright cap switch on a Suhr SL67 MKII and that will show how dramatic the difference can be.
 
I've owned plexis and early metal panels over the years (prolly 5 or 6 not including what I own now} and one of the best I've ever heard was a 1973 PTP metal panel with a Ken Fischer master volume. That thing had tone for days and classic breakup no matter what speakers you ran it thru. My first plexi was a Super Trem that I bought for $425! I miss those days for sure! LOL
 
Greazygeo said:
Obnoxious bright cap, get rid of that sucker.
Click to expand...
Never.
Neuters the amp. At least, in my 72 it does. And, removing it and turning it up to 10, isn't the same as the cap still in, and on 10. That's a fallacy. I changed the brand of 5K bright caps, and the tone changed considerably.
Bright caps are a huge part of the metal panel sound. If you don't like bright, stay away from an early 70s metal panel.

George, I know you prefer darkish amps from your clips.
I totally get why you won't like that 4.7/5K cap.
I have to have it...or my 72 sounds like a Fender. To me anyway lol
 
The bright cap being present, and the filtering throughout being 50/500 in all the can caps are the most noticeable differences in the 70-74 Superleads. And, the higher power PTs that started (I think) in 1970 (unloaded plate voltage of 560v) also contribute to the more aggressive metal panel Marshalls.
 
Racerxrated said:
The bright cap being present, and the filtering throughout being 50/500 in all the can caps are the most noticeable differences in the 70-74 Superleads. And, the higher power PTs that started (I think) in 1970 (unloaded plate voltage of 560v) also contribute to the more aggressive metal panel Marshalls.
Click to expand...
Quite the opposite - lower secondary plate voltage PTs were the ones that had gain for days. Higher voltage with the same stock values everywhere else shift the bias of the preamp tubes to less clipping, not more. Therefore less gain.

Modern designers today know how to use that extra voltage to bump gain (I’ve taught a few of them) but a stock Marshall with a higher B+ will sound more clean and won’t break up with volume.

One of the common mods back in the day for Jose was to install mini step down transformers to get the voltage down. He hated the big PT secondary voltage era.
 
Racerxrated said:
Never.
Neuters the amp. At least, in my 72 it does. And, removing it and turning it up to 10, isn't the same as the cap still in, and on 10. That's a fallacy. I changed the brand of 5K bright caps, and the tone changed considerably.
Bright caps are a huge part of the metal panel sound. If you don't like bright, stay away from an early 70s metal panel.

George, I know you prefer darkish amps from your clips.
I totally get why you won't like that 4.7/5K cap.
I have to have it...or my 72 sounds like a Fender. To me anyway lol
Click to expand...
Yeah that cap is very bright and hard on the ears. Lower settings are not very useful. Higher settings still too bright for me, puts the guitar frequency range too close to the cymbals. The earlier 100pf works better for me.

Oddly enough last few rehearsals I have been using an old Blackface Fender Princeton Reverb, everything on 5 cept reverb and tremolo of course. Surprisingly good sounding setup.
 
glpg80 said:
Modern designers today know how to use that extra voltage to bump gain (I’ve taught a few of them) but a stock Marshall with a higher B+ will sound more clean and won’t break up with volume.
Click to expand...
Gonna take a guess and say you reduce the headroom of one or more of the later stages, and use the higher plate voltage on earlier stages to hit the late stages with a larger signal swing?
 
IMO the main contributor to the higher gain is less NFB. The 100W takes NFB from the 4 ohm tap and uses a 100k NFB resistor. That opens up the power section big time.

I could have sworn I read Jose liked the higher voltage Marshalls but I also thought Jose liked bright.

Regarding the voltages, I mostly agree with the above but will say that there is more to it. I’ve heard high voltage Marshalls have all the gain. My clone is just over 500v at idle when plugged into 120vac and it’s dirty af when I variac it down to 90vac. That’s around 370vdc HT.
 
Last edited:
Lightning said:
Jose did like bright listen to some original Jose modded Marshall’s on YouTube and they are bright which I like.
Click to expand...
Cranked Marshalls have a lot of mids and the lower voltages (and lower watts, i.e. 50W) end up having more than I want even tho it does sound killer. So I tend to prefer brighter 100W too but not the crashy/harsh just with gobs of gain so it warms up as you crank it past the bright cap dominance.
 
Last edited:
You must log in or register to reply here.
Back
Top