# 1967 Super Lead Schematic



## liontato

I am trying to locate a good copy of a 1967 50W (or 100W) Super Lead Schematic. Can anyone point me in the right direction? This is my next build.


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## coldengray

I have a layout saved that a Metro Forum member hosted on his site along with several other. I have a 67 and a transition layout I believe. PM me your email address if you'd like me to send them.


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## ampmadscientist

liontato said:


> I am trying to locate a good copy of a 1967 50W (or 100W) Super Lead Schematic. Can anyone point me in the right direction? This is my next build.



When you build this amp, include screen grid resistors - which may not be on the schematic.
There is a difference between the old and new output tubes which (new) causes screens to draw more current.
This extra screen current can blow fuses when the amp is cranked up loud.

The added screen resistors limit screen current and prevents the problem from happening.


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## liontato

Yes. Thanks for the information. Much appreciated!


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## neikeel

This is a 50w (and yes you will need 1k screen resistors between pin 6 and pin 4 of the outputs, as referred to above):




Regarding the 100w version is t will depend what end of 67 you are after. Early ones had Drake transformers (1202-119 OT and 1203-80PT with a dual rectifier) here you will see on this diagram that one half of the rectifier has been rubbed out and link wires drawn in on the lower part of the PT HT secondary:




Second half of '67 saw the Dagnall trannies with a later schem. more like the later SB.


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## liontato

neikeel said:


> This is a 50w (and yes you will need 1k screen resistors on pin 6 of the outputs, as referred to above):
> 
> 
> 
> 
> Regarding the 100w version is t will depend what end of 67 you are after. Early ones had Drake transformers (1202-119 OT and 1203-80PT with a dual rectifier) here you will see on this diagram that one half of the rectifier has been rubbed out and link wires drawn in on the lower part of the PT HT secondary:
> 
> 
> 
> 
> Second half of '67 saw the Dagnall trannies with a later schem. more like the later SB.


Awesome! Thanks for the help and guidance!


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## ampmadscientist

Pentode connection (normal Marshall output)
The screen resistor mounts between pin 6 and pin 4 on the socket.
Pin 4 is the actual screen connection.
Pin 6 is an unused pin, which is just used to hold the resistor in place.
All your pin 6 (of all output sockets) will connect together, and those will connect to the screen power supply point.

The alternative being: Triode output connection
which gives you 40 watts from a 100W amp...or 18 watts from a 50W amp.

The resistor still mounts between pin 4 and 6 on each socket.
But all pin 6 (on all output sockets) do not connect together.
Instead (on each socket) pin 6 will connect to pin 3 on each individual socket.
The screen power supply point is not used. (remains unconnected to output tubes)

This reduces the output power to a more usable level (suitable for 1X12 inch speaker) less loudness.
The output power amp breaks up earlier, easier to drive it into distortion.

If you are playing in smaller rooms (not stadiums) you will appreciate Triode. It's more realistic.
(as you know, Plexi is incredibly loud thru a 4X12 cabinet)

Then last, it is possible to put a switch in there, to change it between low and high power.
This would be a Pentode / Triode switch.


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## liontato

That is some very useful information. I play some outdoor venues but nothing needing the full volume of a plexi or 4x12. Also play a lot of indoor gigs where volume is always an issue. Do you have a schematic or layout? If not, that is ok as the explanation is clear. I just like to visualize whenever possible. Thanks again!


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## ampmadscientist

liontato said:


> That is some very useful information. I play some outdoor venues but nothing needing the full volume of a plexi or 4x12. Also play a lot of indoor gigs where volume is always an issue. Do you have a schematic or layout? If not, that is ok as the explanation is clear. I just like to visualize whenever possible. Thanks again!


40 Watt or 18 Watt is still very loud. (more than you realize) (depends on which speaker)
If you want the schematic for Pentode / Triode switch...
Go to Marshall JCM 900 schematic. It comes this way from the factory.
http://drtube.com/schematics/marshall/cd0192-100-iss1.pdf

A good place to get any Marshall schematic is Dr. Tube
http://drtube.com/library/schematics/69-marshall-schemas

I will make 1 more suggestion at lunchtime...


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## neikeel

ampmadscientist said:


> A good place to get any Marshall schematic is Dr. Tube
> http://drtube.com/library/schematics/69-marshall-schemas



The drtube site is a good resource for schems, but there are no schems for 67 Superleads (Basses or Trems for that matter).
'67 was a funny year for 100watters (mainly power supply and filtering differences of x3 different types - if you are interested?). The 100watters always had screen resistors (although 65/66 had KT66s and 470R) it was the only 50w that did not have them '67-'69 but they used Mullard or Brimar BVA tubes that could take all sorts of punishment


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## liontato

Awesome! Thanks!


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## AlvisX

I love the shared cathode amps.
I've likely changed all my split cathode amps to shared .
Shared cathode with a 220 /270pf brite cap on one channel...the 470/500 range is a little much for my tastes

The other interesting thing to me about the early amps ,which Im sure is a contributing factor to early "plexi" tone is the lack of the .68uf bypass cap on V2a cathode....that came on later amps
On my homemade amps, I've made this a panel switchable option ...Makes for some great xtra Les Paul sizzle on the ROCK ,when it's on and some great tele twang when it's off

Anyhow ,good luck with the build, liontato.....keep us posted


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## liontato

It will be a slow process. I have the NOS and vintage Mustard caps for the build and a bunch of the resistors. As I get time I'll get transformers and a chassis. I have the board and wire, etc ....a bunch of stuff. Right now I just need time to finish a few other projects and then this is next.


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## ampmadscientist

neikeel said:


> The drtube site is a good resource for schems, but there are no schems for 67 Superleads (Basses or Trems for that matter).
> '67 was a funny year for 100watters (mainly power supply and filtering differences of x3 different types - if you are interested?). The 100watters always had screen resistors (although 65/66 had KT66s and 470R) it was the only 50w that did not have them '67-'69 but they used Mullard or Brimar BVA tubes that could take all sorts of punishment



*"...they used Mullard or Brimar BVA tubes that could take all sorts of punishment..."*

1. Let me make this very clear to you:
The design of the tube was changed, learn this.

The older tube *"Mullard or Brimar BVA"* draws less screen current. It does not need the current limiting resistors.
*It has nothing to do with "taking more punishment."*

2. The new tube is more efficient - it draws much more screen current. *The tube WAS re-designed.*
NOW you MUST install screen resistors, to LIMIT the current.

3. if you do NOT install the screen resistors: the POWER SUPPLY (not the tube) will be overloaded.
*Then the fuses will BLOW.*

4. This information comes from: the Marshall engineers, at the factory. (the engineers who designed the Plexi)
*They taught me THIS - and now I am teaching it to YOU.

Learn the lesson - the new tube is a NEW design.*


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## ampmadscientist

AlvisX said:


> I love the shared cathode amps.
> I've likely changed all my split cathode amps to shared .
> Shared cathode with a 220 /270pf brite cap on one channel...the 470/500 range is a little much for my tastes
> 
> The other interesting thing to me about the early amps ,which Im sure is a contributing factor to early "plexi" tone is the lack of the .68uf bypass cap on V2a cathode....that came on later amps
> On my homemade amps, I've made this a panel switchable option ...Makes for some great xtra Les Paul sizzle on the ROCK ,when it's on and some great tele twang when it's off
> 
> Anyhow ,good luck with the build, liontato.....keep us posted



Shared cathode:
It's inherently un-stable. But you might like the sound of it.
The shared cathode designs (marshall and fender etc...) were all changed to split cathodes....to many problems w/ oscillations, etc...


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## AlvisX

ampmadscientist said:


> Shared cathode:
> It's inherently un-stable. But you might like the sound of it.
> The shared cathode designs (marshall and fender etc...) were all changed to split cathodes....to many problems w/ oscillations, etc...



Yep, I like the sound of it , a lot
It's a tone that people chase
I don't recall experiencing any oscillation issues due to a shared cathode configuration ,yet...


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## danfrank

AlvisX said:


> Yep, I like the sound of it , a lot
> It's a tone that people chase
> I don't recall experiencing any oscillation issues due to a shared cathode configuration ,yet...



Shared cathode input stage doesn't oscillate any more than a split cathode stage does. If it's oscillating it's most likely due to bad wiring layout or bad design. What a shared cathode input stage WILL do is have cross-talk between both channels from the signal of one cathode feeding over to the other cathode. In a guitar amp this usually doesn't present problems. This is why Marshall went from shared cathode to split cathode.
Sharing the cathode in two successive stages on the same channel may cause instability problems though. Fender didn't do this; they would always share cathodes from 2 different channels and the same stage topically so the signal on both of the shared cathodes are in phase with each other. This may also cause cross-talk between channels, depending on the value of the cathode capacitor.

The other "advantage" of a split cathode is that each channel can have a much more distinct sound that the other by modifying the cathode resistor/cap values.


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## AlvisX

danfrank said:


> The other "advantage" of a split cathode is that each channel can have a much more distinct sound that the other by modifying the cathode resistor/cap values.



Brite cap values can make each channel very distinct on a shared cathode amp.
For me , what evolved into "lead" values are a little TOO distinct for my ears


I suppose there's no right or wrong way to "Marshall". 
The way I do it, shared really works


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## Kris Ford

Sounds like Alvis is a Super Bass kinda guy.


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## Appetite4distortion

I was a split cathode guy but I've grown very fond of shared as the age goes on and the less gain I use.
Indeed shared is so much better with clean and slight crunchy tones.
I think Marshall changed to split cathode to keep the tone tigthter and less muddy with distortion. Shared has too much "information" to pass (especially bass) when you increase gain and want tight distortion.
Fact is, later 60s everybody began to ask for more gain.
Of course a shared under a lot of gain would oscillate and feedback.
But these "unwanted" nuances all adds up to tone, and when kept under control (i.e. without too much gain) are what creates the most beautiful guitar tones IMO.
If you do not want any oscillation is that simple, plug into digital gear and problem solved. But the sound is not so inspiring..at least for me...

Ampmadscientist, the marshall engineers who created the plexi I think are long retired and playing with their grandchildren, fact is some of them are buried already: did you speak with those who were in the factory in the 60s or did you speak with the actual engineers who are creating the modern amps?


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## AlvisX

Kris Ford said:


> Sounds like Alvis is a Super Bass kinda guy.



More or less..45/Bassman/ Super Bass...It's a proven method 
Kossoff
Malcolm
Doyle II
All SB users......good company 

You know how guys would change their bass spec amps to lead specs..., I'd do just the opposite
lift the .68uf on V1b & share it with V1a , change the .0022uf coupler to .022, swap the brite & treble caps to 250pf.Sometimes I change the output couplers ,sometimes not. My Trem 50 came with Wima .1uf ..pretty sweet
I suppose I like a combination of bass & lead spec, but I definitely don't care for super brite values much

When I was a kid ,before I got all these Marshalls ,I had a bassman for awhile ...a real one ,as maybe then the HIGH price for one was $400 then . I really liked how each guitar I plugged into it ,sounded the way I thought they should sound. I got crunch with the LP Junior & twang with the tele & Danelectro (without cuttin your head off) I think that kinda got me tuned in to where I wanted the Marshalls to go


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## Kris Ford

Don't forget Gary Moore!


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## ampmadscientist

Shared cathode doesn't always oscillate, but it can.


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## mickeydg5

I like my old Tweed Bassman just as much or more than any other amplifier. No oscillations.


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## AlvisX

Kris Ford said:


> Don't forget Gary Moore!



Right 
When I was out with him he had a JCM 800 era 1959 that I coveted 



ampmadscientist said:


> Shared cathode doesn't always oscillate, but it can.



With Marshalls came a shift to higher MU preamp tubes .I could certainly see a the possibility 



mickeydg5 said:


> I like my old Tweed Bassman just as much or more than any other amplifier. No oscillations.



There's an amp I wish I'd kept. The good thing is ,I figured out how to cook up a pretty good tweed bassman outa silverface carcasses......with solid state rectifiers already in 'em


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## kilo95

Hello all. Sorry for resurrecting an old post. I'm considering building the 100w version of the SuperBass. Does anyone have a layout of it that they'd be willing to share? my email is my user name at aol.com. Thanks


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## neikeel

Try this (minus the trem section):




or this:


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## Pete Farrington

neikeel said:


> you will need 1k screen resistors between pin 6 and pin 4 of the outputs


Did ampmadscientist ever provide evidence to back up his assertion that EL34 design changed in the latter part of the 60s, such that the screen grid current draw of valves made after then increased?
Other than his personal testimony 
I wonder how such a change might have increased efficiency? To my thinking, it would have the opposite effect


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## neikeel

Pete Farrington said:


> Did ampmadscientist ever provide evidence to back up his assertion that EL34 design changed in the latter part of the 60s, such that the screen grid current draw of valves made after then increased?
> Other than his personal testimony
> I wonder how such a change might have increased efficiency? To my thinking, it would have the opposite effect


I could not go down that particular rabbit hole!


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