Definitive 12xxx-series EVH spec? Warning: long post

tWreCK

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I know this topic has been discussed & beaten to death but my quest to build an EVH-spec replica has left me with unanswered questions so please bear with me :) I'm not an amp tech nor engineer - just a player trying to gather as accurate info possible. I apologize for the longwinded post (it's hard to summarize all this info).

In my research here and on other boards (Metroamp etc) I've come across several conflicting viewpoints/opinions on Eddie's "main plexi". My main objective is to determine the "definitive" EVH-spec 12xxx once and for all in reference to what is considered a typical stock '68 12xxx. For my build I'm going the NOS route as much as possible.

Here goes - according to Friedman's account this is what he documented when servicing Ed's main plexi (posted on the Metropoulos forum by leadguy):

Split cathode V1a 250uF/820,V1b .68/820
All coupling caps are 0.022uF,Bright channel coupling cap is 0.0022uF
bright cap on vol pot 0,005uF
470k mixer resistors
500pF mixer bypass cap
Bypass cap on V2a is .68uF and a 220uf to 470uf
33k/500pF tone stack combo
100k NFB resistor at 4 ohm tap
220k bias splitter resistors
0.1 uF cap on presence control
.022uf output couplers

Merren's account 1980:

"To try to wrap up is ED thing...
His head was a 67/68 and he had the first stage valve with BOTH cathodes tied together sharing the same 820 ohm resistor that was bypassed with a 330uF blue cap...

His treble cap was a round shaped ceramic that was a 250pF that said MURATA ... With 56K on the tone circuit feed..

One of the 470K mixer resistors was bypassed with a round hollow tubular MURATA cap 500pF... If memory serves me right on the value, or it was a 330pF..I will check my notes....

The real kicker, his phase-inverter "get-rid-of-the-FIZZIES" cap was a 100pF instead of the normal 47pF ....and this my friends is how the "brown sound" with that added compression happens..

Oh, BTW those 820 ohm resistors were carbon-comp and drifted in value up about 1.1K and make the amp much more gainy and warmer, since these re-bias the 12AX7 valves in a bit more non-linear region..

I am pretty sure the feedback resistor was a 47K ...I will have to check my notes...

The filter cap in the center of the board was a dual 16uF gray RS cap...

The screen filtering was 2 DALY 32uF light-blue caps in series... The voltage doubler were 2 100uF DALY royal-blue caps...

Rear cap on top of chassis was a royal-blue HUNTS 32uF or 16uF...need to check notes..

The value of the coupling cap between V1 and V2a....022uF.

At least that was what it was in 1980..."

(I'm unclear as to what Chris' affiliation with EVH was or where he got this information....)

Next in line - Plaap's account (a friend of Van Wheelden) who supposedly helped "restore" Ed's amp:

"1.The first 820 ohm resistor (carbon type) measured a little over 1K. It was bypassed with a blue 330uF resistor. can

2.His treble cap was a 250pF Murata flat ceramic one. The cap across his 470K was a Murata hollow round 330pF. cap

3.His second stage 820 ohm (which also measured a little over 1K, was also bypassed with the exact same type 330uF blue colored cap that was on the first cathode resistor.

4.The filtering caps for the middle of the board were gray colored RS caps that had dual 16uF values.

5.The screens were 2 blue caps in series (DALY 32uF's).

6.The voltage doubler were two big blue caps (100uF DALY's). The one on the outside was a blue Daly - and was a single 32uF.

7.The feedback resistor was a 47K of unknown origin.

8.His power transformer was the smaller one of that era. His OPT was also the smaller one with 1.5" stack.

The amp was either left stock into a load resistor or, a big Ohmite(or other) power resistor was placed somewhere in the circuit to cut the power of only the output stage meaning Sylvania 6CA7's were the only valves to hold up to this.

If this is true - doesent this kinda dispel the whole 'special' 67 slp 100 myth ...as almost all amps of that year had pretty much identical configurations (with the small exception of the 330uf cap on the second preamp stage?

Dankuwell !(dutch for many thanks)
Plaap"

In reference to the above I found a post by Master Keeper (on the Metroamp forum) regarding the specs of his stock '68 12xxx:

Master Keepers #12267 Series specs:
Split Cathode V1a - 250uF/820; V1b - .68/820
All coupling caps are - 0.022uF
Bright channel coupling cap - 0.0022uF
Bright cap on Vol pot - 0,005uF
470k mixer resistors
470pF mixer bypass cap
V2a bypass cap - .68uF
33k/556pF tone stack combo
47k NFB resistor at 4 ohm tap
220k bias splitter resistors
0.1 uF cap on presence control

Mains - 50uF (my comment: 2 x 100uF in series?)
Screens - 32uF
PI – (32u-40uF)
and dual 32uF for preamp

Because of the varying info it's hard to tell if Ed's #1 amp was bone stock or if it had been tweaked? Furthermore, are all these observations by the different people in regards to Ed's #1 plexi or were there other amps in the mix? It's not hard to imagine Ed owned or had access to multiple vintage Marshall's. As far as I can tell (in strictly non-expert terms) the differences between Ed's main amp and a typical stock '68:

mixer cap: 500pF EVH > 470pF stock '68
tone stack: 33k-500pF EVH > 33k-556pF stock '68
NFB resistor: 100k-4ohm tap > 47k-4ohm tap stock '68

according to Plaap/Merren the treble was a 250pF ceramic Murata and the mixer bypass was a 330uF tan hollow round Murata. PI cap was a 100pF grey tubular(?) instead of the typical 47pF flat silver mica.

Filtering:

preamp: dual 16uF grey RS (Plaap/Merren) vs dual 32uF (Friedman/stock '68)
mains: 100uF x 2 (royal blue Daly)
screens: 32uF x 2 (light blue Daly)
PI: 32uF (blue Daly/Hunts)

Plaap/Merren:
PT: Dagnall T2562?
OT: Dagnall 1.5" C1998

Friedman:
PT: ?
OT: Drake 2" 1202-132
choke: 70's c1999 (?)

If I've left out and/or misinterpreted anything please let me know. Feel free to fire away with your comments/viewpoints of the above. I'm just trying to arrive at what is considered to be the "definitive EVH-spec. If we can arrive at some consensus perhaps we can create a "sticky" for future reference (or maybe it's already been done)? I hope all the resident Marshall gurus will chime in i.e. Tazin Neikeel etc.
 

william vogel

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Well, they don’t agree and depending on what it really was, it would have sounded quite different. The Friedman example is pretty close stock to what one would expect from a 68 12000 series and the Merren example would be modded or more like a 67. Who knows for sure but unless Merren and Plaap traded notes, we’ve got similarities between two and we’ll never know for sure.
 

TAZIN

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I don't believe that Plaap was a friend per-se of Peter Van Wheelden, rather he lived somewhat near by (maybe 20 miles away) and probably may have utilized his services in the past. Either way, he knew of Van Wheelden and where he was located. Plaap's account of the amp mirrors Chris Merren's to the point where Chris even said he copied his info from previous posts verbatim and he (Chris) didn't put much stock in the fact that Plaap's acquired the info first hand from Van Wheelden. Anyhow, Merren's backstory is that he lived around LA back then and crossed paths with Eddie occasionally which somehow led to him being able to see the amp. Interestingly, Chris has his late 1967 Super Lead setup with almost the exact same specs he posted back in '98 - '99. So this begs the question whether Chris listed the specs based on his amp or Ed's amp since the late '67 Super Lead tends to have the component types he mentions whereas the mid '68 Super Lead's do not.

Friedman's account of the amp matches Soldano and meshes with the reputed amp photos posted by Voodoo Amps I believe. I would say there's a 100% chance that Friedman did see the amp so his info is probably the most accurate. When it came to restoring the amp, it seems the only real thing that Friedman guessed on was the filtering scheme which tells me that part of the amp was messed with the most over time. So, he went with a 'typical' 12series filtering scheme. With that said, the only real other deviation on the 'typical' filtering that I've seen would be the use of two 20uF/450v caps for the preamp filtering which was used on some of the 12series amps built around the same time frame as Ed's. The other thing Friedman mentioned was the the Middle pot was a 50K verse the traditional 25K.

So, this is your 'typical' stock specs for a '68 Super Lead (split-cathode) built around the same time as Ed's:
Split Cathode V1a - 250uF/820; V1b - 0.68uF/820
All coupling caps are - 0.022uF
Bright channel coupling cap - 0.0022uF
Bright cap on Vol pot - 0.005uF
470K mixer resistors
RS 500pF mixer bypass cap; Some had a LEMCO 556pF
V2a bypass cap - 0.68uF
33K/500pF (RS) tone stack combo; Some had a LEMCO 556pF
47K NFB resistor from Speaker jacks; Except for #12267 has NFB from 4 ohm tap
220k bias splitter resistors
0.1 uF cap on presence control
47pF ceramic disc (Murata) or a 41pF tubular ceramic cap (gray clr.) Phase Inverter plate balancing cap (Fizz cap)

Mains - two HUNTS 100uF/350v
Screens - two DALY 32uF/450v
PI – HUNTS 50 - 50uF/450v
Preamp - HUNTS or RS 32 - 32uF/350v; OR two SYNCRO 20uF/450v

Ed's amp was probably not stock when he bought it. Hell, it was serviced in the Autumn of 1978 and parts were changed so by the time all these guys saw the amp who knows how many changes occurred. So, the current deviations from 'stock' would be the following:

100K NFB.
50K Middle pot...Even though it maybe be 'stock' from the factory.
Additional V2a cathode bypass cap (220uF - 470uF).

Also worth mentioning:
The Output transformer...Although it's currently a Dagnall C1998.
The choke...Even though it may have 'stock' specs, it was an early '70s unit. Not sure if Dave changed this out to a C1999...
BTW, the Mains transformer looks like a stock Dagnall T2562.
 

tWreCK

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Thx for the informative post Tazin. That's exactly the type of info I was hoping to get. Very interesting info on the Plaap/Merren account.

Judgjng by all the info the safest bet for an EVH '68 is to go stock (at least to start with) so that's what I'm going to do. I can always tweak it later if need be.
 

TAZIN

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Thx for the informative post Tazin. That's exactly the type of info I was hoping to get. Very interesting info on the Plaap/Merren account.

Judgjng by all the info the safest bet for an EVH '68 is to go stock (at least to start with) so that's what I'm going to do. I can always tweak it later if need be.
FWIW, there's a guy on youtube named Jim Gaustad who recently did a few videos for the VH1, VH2 and Fair Warning tones and I think they're about as close as it gets. His amp; a Marshall clone, is setup with the Friedman specs.
 

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