Wish Parameter that switches between PP and SE exposed as a option

Sorry about that ..., @FractalAudio will understand it, probably better than any of us here !

PP = Push/Pull
SE = Single Ended

If you've been following Jim Gaustad's - EVH - Van Halen 1 & Van Halen 2 deep dive you'll understand it better ....

Basically it's speculation based on extensive trial & error that Eddie pulled tubes out of his 100 watt Plexi to tame the voulme ( no surprise there, a lot of people did ! ) ..., but in doing so, he did something completely unorthodox ..., and stumbled on something that a lot of us think is very magical relative to Marshall Plexi tone !
 
I put this in a different thread ..., but here's the known specifications of Eddie Van Halen’s 1968 Superlead Plexi # 12301 ….

  • Heyboer Transformers (Dagnall clones)
  • 6CA7 Output Tubes
  • Sylvania 12AX7 Preamp Tubes
  • 50K mid-pot
  • Split cathode on V1a (250µF/820Ω) and V1b (.68µF/820Ω)
  • All coupling caps: 0.022µF
  • 470K mixer resistors
  • 500pF red tubular mixer bypass cap
  • Fat Cap mod: .68µF and 250µF on V2a
  • Tone stack: 33k/560pF Lemco combo
  • 100K NFB resistor from 4Ω tap
  • 220K bias splitter resistors
  • 0.1µF cap on presence control
  • 0.022µF output couplers

Power filtering:
  • [2] 100µF F&T ( mains )
  • [2] 32µF F&T ( screens )
  • [1] 100µF LCR ( phase inverter )
  • [1] Dual 33µF x 33µF F&T ( preamp )

Based on past comments by Cliff I believe that we have models w/ the majority ( if not all ) of these specs already. They may not all be contained in the same amp ..., only Cliff would know for sure !

But when Eddie pulled tubes to lower the volume, evidently he pulled Tubes 4 & 5 ( or maybe 6 & 7 ) ..., and that's the unorthodox part !

To maintain the Push / Pull of the Marshall power amp section, you "should" pull either Tubes 4 & 7 ( or 5 & 6 ) .... Pulling 4 & 5 essentially turns the power amp from Push / Pull to Single Ended and it supposedly increases the gain of the amplifer, leans out the bass frequencies and makes the distortion character quite a bit more aggressive.

Jim Gaustad found a quote from a Ted Templeman interview in San Francisco years ago, where he said the Eddie told him "he knew which tubes to pull to make the amp sound a lot meaner" !
 
R.D. said:
I put this in a different thread ..., but here's the known specifications of Eddie Van Halen’s 1968 Superlead Plexi # 12301 ….

  • Heyboer Transformers (Dagnall clones)
  • 6CA7 Output Tubes
  • Sylvania 12AX7 Preamp Tubes
  • 50K mid-pot
  • Split cathode on V1a (250µF/820Ω) and V1b (.68µF/820Ω)
  • All coupling caps: 0.022µF
  • 470K mixer resistors
  • 500pF red tubular mixer bypass cap
  • Fat Cap mod: .68µF and 250µF on V2a
  • Tone stack: 33k/560pF Lemco combo
  • 100K NFB resistor from 4Ω tap
  • 220K bias splitter resistors
  • 0.1µF cap on presence control
  • 0.022µF output couplers

Power filtering:
  • [2] 100µF F&T ( mains )
  • [2] 32µF F&T ( screens )
  • [1] 100µF LCR ( phase inverter )
  • [1] Dual 33µF x 33µF F&T ( preamp )

Based on past comments by Cliff I believe that we have models w/ the majority ( if not all ) of these specs already. They may not all be contained in the same amp ..., only Cliff would know for sure !

But when Eddie pulled tubes to lower the volume, evidently he pulled Tubes 4 & 5 ( or maybe 6 & 7 ) ..., and that's the unorthodox part !

To maintain the Push / Pull of the Marshall power amp section, you "should" pull either Tubes 4 & 7 ( or 5 & 6 ) .... Pulling 4 & 5 essentially turns the power amp from Push / Pull to Single Ended and it supposedly increases the gain of the amplifer, leans out the bass frequencies and makes the distortion character quite a bit more aggressive.

Jim Gaustad found a quote from a Ted Templeman interview in San Francisco years ago, where he said the Eddie told him "he knew which tubes to pull to make the amp sound a lot meaner" !
Click to expand...
That doesn’t change the amp from PP to SE… it just removes one half of the power amp circuit, totally messes with output impedance and would most likely destroy an output transformer.

Eddie was known to ‘embellish’ a bit LOL.
 
Domct203 said:
That doesn’t change the amp from PP to SE… it just removes one half of the power amp circuit, totally messes with output impedance and would most likely destroy an output transformer.

Eddie was known to ‘embellish’ a bit LOL.
Click to expand...

I'll admit that I don't understand the situation ....

But that said, Dave Friedman on Friday's Tone-Talk basically confirmed that it could be done, especially if you were using a Variac in combination to lower the voltage ....

He pulled tubes from a couple of his old Marshalls and measured the effect ....
 
Domct203 said:
That doesn’t change the amp from PP to SE… it just removes one half of the power amp circuit, totally messes with output impedance and would most likely destroy an output transformer.

Eddie was known to ‘embellish’ a bit LOL.
Click to expand...
Yes, it changes the amp from PP to SE. Basically it simply disconnects one half of the OT primary.

Now I'd have to think about the ramifications from a matching standpoint.
 
I knew it would only be a matter of time until someone tried it !



It's subtle but there is a difference ....
 
R.D. said:
I knew it would only be a matter of time until someone tried it !



It's subtle but there is a difference ....
Click to expand...

Very cool. Those examples, especially with the pulled tubes, seem to replicate that “Yeowwww” purring-tonal-chewiness that you hear on held chords that Pete Thorn and Dweezil referenced on the Runnin’ With The Dweezil podcast. I’m on a quest for that…
 
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