Tweaking Super Lead specs

[Dave L]

Hi guys, I got a fresh-looking ´75 Super Lead a while back, and even if it sounds great as is you always end up second guessing yourself with these. The question is, if you were leaning toward an earlier metal panel spec, say 69-70, which changes would you start your tinkering with? From looking around a bit the negative feedback and the V2 bypass cap seem like the big ones...?

The transformers and voltages are what they are, I suppose, but seems like they´re mostly pretty high B+ after the plexis anyway, and it´s still Dagnalls even if they went to other models in the early 70s somewhere.

I will not be doing this myself, by the way. I´ll have a good tech do it and pick his brain too, I just want to come in a bit prepared.

 

[Kapo_Polenton]

I think just doing the Friedman tweaks he mentioned in that Pete Thorn shop video a while back where they were chasing the VH thing for that video Pete did. Very basic tweaks and the rest is your hands and a pickup with decent gain. Honestly, 3 to 4 changes will get you there.

 

[Anje]

My initial thoughts on that case:
- always better to check / share what is the exact circuit details of your amp to start with; as variations may have happened.
- evolution of transformers is an important factor to me between those different eras = not easy to change that without seriously impacting your amp if its stock & good condition
- power filtering is a less invasive change that can have quite an impact in the amp sound/feel
- if you want to tweak components on the board, beware of those early PCB that can be fragile
- my own personal opinion is that I would not want to mess with an original amp too much trying to "backdate" it; I'd rather look into finding a proper era base to work with.

 

[Greazygeo]

100pf bright cap

 

[Anje]

SL specs for 68 & on would be 5k bright cap; I personally always preferred that stock 5k value for the bright cap on old NMV Lead amps.
That being said, experimenting with different values is easy I agree.

 

[Racerxrated]

Big bright cap, as others mentioned will increase the gain. Look for a Lemco if possible, believe it or not different brands sound different as I've tried a few different brands of Ceramic 5Ks. Lemco were the stock caps. Experimenting with more Plexi filtering (lower than the 70s on to today) will really change how the amp responds/feels. I have a 72, now modded, and a late 68/early 69 that sounds amazing but ghosted like crazy when cranked....has lots of gain totally stock. The stock filtering was a mix of previous 67-68 and what would increase later in 69. The PI is 50/50 450v, Mains 32/32/350, screens also 32/32/350 but pre 50/50/500. I increased the mains to 50/50/500 and no more ghosting. The plexi feel is still there. I'm gonna experiment with lower pre filtering at 32/16/500 and see if that might be better. I realize though that those values could re introduce ghosting....

This amp has none of the EVH 'factory' mods....no fat cap on V2A, no 50k mid pot, nothing in the NFB other than stock yet it easily has as much gain as a 2203, maybe a touch more. That's with the bright Vol on 7, rhythm Vol on 8.

 

[Anje]

Yes, some particular amps kind of stand out; most probably because of some mix of component / slight circuit variation?
I have a '72 lead 50w in particular, that is just a monster gain amp. No other '67-71 I've had or played has been close to this one for some reason.

 

[harddriver]

1975 Superlead should be the following specs. 820/330uf V1A, 2.7K/.68uf V1B, 820/.68uf V2A, NFB should be a 100K resistor on the 4 ohm tap. Sometimes Marshall left the .68uf off of V2A and sometimes used 1K V2A cathode resistors instead of 820. My 72 SL has a 1K instead of an 820 ohm on V2A but it did have the .68uf cathode Mustard bypass cap stock. Alot of amps seem to hit or miss in this era whether or not they got the .68uf for V2A.

From 72 onward Marshall was still using up some RS/Lemco 500/560pf mica caps on the 470k/470K mixer and the tonestack which is more plexi. My 72 had standard brown ceramic 500pf cap on the 470K/470K mixer, a 5000pf Lemco bright cap, 560pf RS Mica cap on the tonestack and 100K NFB resistor on the 4 ohm tap.

Also starting in 69/70 amps could also get the red tubular ceramic dogbone caps, as well as the mica, or small round ceramic disc cap in the mixer and tonestack locations, it just depended on what parts Marshall had when your amp got built really.

As these small brown ceramic disc caps age they can get kinda harsh sounding, my 72 was pretty strident in the highs, super aggressive and harsh which I didn't care for so when I recapped the entire amp , V1A, 10 uf bias caps 50/50, filter caps a couple of years ago I used the standard 68/69 plexi specs. I removed the small 500pf ceramic disc cap from the 470k/470k mixer and installed an NOS RS 560pf mica cap I still had lying around as my amp already had an RS 560pf mica cap in the tonestack. I also replaced the original Lemco 5000pf cap with a new NOS 5000pf Mallory cap. I did keep the original 100K NFB resistor but I put the NFB on the 8 ohm tap like a plexi. The 100K NFB will make the amp a bit more ratty and just tad looser so if you want the plexi clarity, tightness and headroom you will need to change the 100K to a 47K NFB resistor or piggyback another 100K on top of the existing 100K which will give you 50K NFB and then put the NFB tap on the 8 ohm impedance tap.

I found after I removed the small brown ceramic cap from the 470K/470K mixer and installed the nos rs 560pf mica as well as the old 5000pf lemco the amp got more quiet and less hissy and more in line with my 68 Plexi which I really love, I also replaced the stock V1B .0022uf metal tubular polystyrene coupling cap with an NOS Mustard cap and replaced the power cord and redid the grounding on the plug. I'm running a Lar/Mar PPIMV in place of the presence pot and moved the presence pot down into the empty hole for the polarity switch.

If you like the more ratty, more aggressive less headroom tone and you still feel the amp sounds harsh try replacing the 470K/470K with an NOS CDE silver mica, even the newer CDE's are good and possibly the old Lemco/RS 5000pf bright cap.

I really like the 5000pf bright channel bright cap as it really brings out the amps aggressive crunchy nature that is a Marshall Plexi/Superlead IMHO but some people like the bright cap lowered to 1000pf, 500pf or just removed which make the amp more like a Super Bass, if you like it that all that counts. I also kept the stock 72 filtering across the board as my 72 is a 50 watter it has 50uf/50uf preamp, 100uf mains, 50 screens, 50uf Phase Inverter and it's not that far off of my 68 plexi and the 69 SL I built with 100% NOS parts was all standard 50/50uf SL filtering and that amp kicked all sorts of ass, every bit as good as my 68. For a 69 and up 100 watter it will be 50uf mains, 50uf screens, 50uf/50uf preamp and 100uf Phase Inverter. For a 68 it is 50uf mains, 32uf/32uf in series for16uf screens, 32uf/32uf preamp and either 64uf or 100uf for the phase inverter, I prefer 100uf, less ghosting with 100uf.

Good luck, let us know how the expermientation goes.

 

[SpiderWars]

I haven't A/Bd them but some claim the A&R caps sound better than the F&T. So if you're doing the filter caps that's something to consider.

Lots of stuff to digest above so I won't add much. If it's over 500V B+ you might consider lowering the bias splitters. My SL is always on a variac so I left mine at 220k. But at full voltage and cranked mine is really hard on tubes. It arced one once...but the amp and the tube somehow survived.

 

[harddriver]

I haven't A/Bd them but some claim the A&R caps sound better than the F&T. So if you're doing the filter caps that's something to consider.

Lots of stuff to digest above so I won't add much. If it's over 500V B+ you might consider lowering the bias splitters. My SL is always on a variac so I left mine at 220k. But at full voltage and cranked mine is really hard on tubes. It arced one once...but the amp and the tube somehow survived.

My 68 had all F+T's except the preamp and I changed them all out for all ARS caps and I think the amp sounds and feels better now. Not the it sounded bad with the F+T's I just feel the difference was noticeable. That amp also was running an NOS 32uf/32uf Erie cap for the preamp so maybe that was why the F+T weren't so noticeable to me but the new ARS caps in the mains, screens and PI did seem to make a difference in the amp as intangible the difference may be on paper.

 

[Racerxrated]

My 68 had all F+T's except the preamp and I changed them all out for all ARS caps and I think the amp sounds and feels better now. Not the it sounded bad with the F+T's I just feel the difference was noticeable. That amp also was running an NOS 32uf/32uf Erie cap for the preamp so maybe that was why the F+T weren't so noticeable to me but the ARS cal in the mains, screens and PI did seem to make a difference in the amp as intangible the difference may be on paper.

Yep I'm in the same camp as you; I definitely can tell the difference between F&T caps and ARS after changing out F&Ts a few times in favor of ARS. I recall Larry mentioning that F&Ts tend to make an amp sound a bit more HiFi vs ARS that stay true to the original Daly/LCR British tone.

 

[skoora]

I wouldn’t change anything. If it sounds good to you, leave it alone. Unless you’re very familiar with older circuits and can express clearly what you want the 75 to do, that it doesn’t, you’ll be on a fools errand of giving a tech money to not necessarily end up in a happier place. I recently had a ‘75 50 watter tuned up to my liking but I knew exactly what I wanted it to sound like and we got it there. But I also was there as he made tweaks and playing.
Basically don’t start chasing what you don’t even know your chasing.
But…if you are familiar with earlier circuits, how they feel and sound and the 75 isn’t quite doing it for you, absolutely go for it.

 

[SpiderWars]

Yes, some particular amps kind of stand out; most probably because of some mix of component / slight circuit variation?
I have a '72 lead 50w in particular, that is just a monster gain amp. No other '67-71 I've had or played has been close to this one for some reason.

My opinion is that much of it is in the transformers. I've built amps and certain amps just have it and certain ones just sound fine. And tweaking circuit components never changed it, they all usually sounded best with stock values or EVH spec if you're into that. But the ones that had it just had it and the others just sounded fine.

 

[skoora]

My opinion is that much of it is in the transformers. I've built amps and certain amps just have it and certain ones just sound fine. And tweaking circuit components never changed it, they all usually sounded best with stock values or EVH spec if you're into that. But the ones that had it just had it and the others just sounded fine.

Kind of agree with this. My amp sounded good before messing with it, so it just got a refined, not transformed. If I found a NMV Marshall and it was harsh, brittle or had no sweetness to it, I would pass and not attempt to mod those aspects in.

 

[harddriver]

Yep I'm in the same camp as you; I definitely can tell the difference between F&T caps and ARS after changing out F&Ts a few times in favor of ARS. I recall Larry mentioning that F&Ts tend to make an amp sound a bit more HiFi vs ARS that stay true to the original Daly/LCR British tone.

I would definitely agree with Larry's statement.

I see Larry finally gave in and used all new ARS fitler caps in his latest PMM DINO builds so he must have given ARS the nod.

I came at it pretty much with a skeptical outlook really. I had ran that amp for over 15 years with the F+T's and that NOS Erie 32/32uf in the preamp and I didn't think I would experience much difference at all. Much to my chagrin I found the amp to sound better and feel better all around, I don't know if I would call the F+T's grainy or not as alot of people do, maybe I would say it was less harsh.

For me it was difficult to pinpoint in minutia and compare and contrast the two sets of caps, I just know the amp sound and feels better now. My 84 JCM800 Cameron HG Jose is all ARS and my 72 was recapped with all ARS 50uf/50uf caps replacing 30+ year old LCR's and that amp is spectacular now, quiet, gainy, no hiss.

I have full ARS cap sets here for my Splawn modded 1979 2203, my Fender Bandmaster and my Marshall 1x12 2203 combo amp. These cap jobs are on my fall project list.

 

[harddriver]

My opinion is that much of it is in the transformers. I've built amps and certain amps just have it and certain ones just sound fine. And tweaking circuit components never changed it, they all usually sounded best with stock values or EVH spec if you're into that. But the ones that had it just had it and the others just sounded fine.

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There was just something going on with the transformers especially the Output transformers in 1968-1972 that have that intangible mojo that just define a great sounding Marshall.

I've seen some guys trying to get top dollar with replaced output and power transformers and I would not give top dollar if I wanted a vintage 68/70 Marshall. I could probably let a new power transformer with an original Dagnall C1998 slide for a player but I was collecting they would have to original for sure.

 

[skoora]

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
There was just something going on with the transformers especially the Output transformers in 1968-1972 that have that intangible mojo that just define a great sounding Marshall.

I've seen some guys trying to get top dollar with replaced output and power transformers and I would not give top dollar if I wanted a vintage 68/70 Marshall. I could probably let a new power transformer with an original Dagnall C1998 slide for a player but I was collecting they would have to original for sure.

Yeah, my ‘75 has all around MM iron and the purist in me didn’t like that when I first saw it, but it sounded undeniably good to me and it made the price a lot more friendly. Maybe the replaced iron was better than what it had in ‘75? Normally I avoid post ‘73 as after that has been too hard sounding, IME.

 

[Greazygeo]

That 5K bright cap, ugh freaking terrible sounding. All high mid thwack thwack thwack on the low strings. Can’t stand that sound.
Sure if you play on ten and don’t have to hear the cap. 100 pf gives the gain and round low end for palm mutes. None of that thwackin shit.

 

[skoora]

That 5K bright cap, ugh freaking terrible sounding. All high mid thwack thwack thwack on the low strings. Can’t stand that sound.
Sure if you play on ten and don’t have to hear the cap. 100 pf gives the gain and round low end for palm mutes. None of that thwackin shit.

Yeah, not a fan of the super aggressive bright caps either. My 69 metro build from yore, I settled on a 500 but I also wasn’t doing the V2a bypass cap either. It was still a flamethrower when cranked but was really versatile for edge of breakup, clean and AC/DC tones.

 

[FourT6and2]

Big bright cap, as others mentioned will increase the gain. Look for a Lemco if possible, believe it or not different brands sound different as I've tried a few different brands of Ceramic 5Ks. Lemco were the stock caps. Experimenting with more Plexi filtering (lower than the 70s on to today) will really change how the amp responds/feels. I have a 72, now modded, and a late 68/early 69 that sounds amazing but ghosted like crazy when cranked....has lots of gain totally stock. The stock filtering was a mix of previous 67-68 and what would increase later in 69. The PI is 50/50 450v, Mains 32/32/350, screens also 32/32/350 but pre 50/50/500. I increased the mains to 50/50/500 and no more ghosting. The plexi feel is still there. I'm gonna experiment with lower pre filtering at 32/16/500 and see if that might be better. I realize though that those values could re introduce ghosting....

This amp has none of the EVH 'factory' mods....no fat cap on V2A, no 50k mid pot, nothing in the NFB other than stock yet it easily has as much gain as a 2203, maybe a touch more. That's with the bright Vol on 7, rhythm Vol on 8.

I like the higher filtering. 50uF + 50uF everywhere. If not more. Remember that Marshall runs the reservoir caps and screen caps in parallel-series, so even though you have FOUR 50uF caps for each, the total capacitance is still only 50uF. Except for the phase inverter, which gets 100uF.