A new clip to try my theory

[Ralle]

http://www.pleximods.com/evhspec.html


From the Plexi Palace:

(1) By Mark Cameron from pictures taken in the early 80′S.
There ARE small tone altering and/or gain altering mods.
I do have pic’s so I CAN physically see that the amp has a split cathode arrangement.
…the cap on v2(330uf) cathode.
…its a 2.7k/.68 and the resistor looks like the stock part (but I don’t think it is) but the cap is one of those yellow square type from the 70′ Marshall’s. From the circuit card It looks like it came stock with this arrangement. The post that is pressed in looks stock too which tells me more than anyone could. In the pics the serial # is 12301.

(2) ****** 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 grey 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…

(3) Plaap (a friend of Peter Van Wheelden who restored Eddie’s amp.)
Edwards amp’s internal measurements were as follows:
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 coloured cap that was on the first cathode resistor.

4.The filtering caps for the middle of the board were grey coloured 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 – doesn’t 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

This is a great example of what I mean... the only speq here that works is the one MarkC describes...
The other speqs might have been Ed's amps, but not the one of the amps we all are looking for... Mark C says 2.7k...
What does that say?

[Ralle]

Didn't add that much when I tried that a while back !

Perhaps it's the combination of having the Normal channel volume pot turned up to 2 o'clock in conjunction with the 2.7K/0.68uF on v1b and the 10nF-12nF coupling capacitor on the bright channel?

And I voted for the 2.7k/.68u/.022u... and I allways have vol II at 2 aclock... can't do without it... we're getting close... well, in the right direction at least

[Tazin]

And I voted for the 2.7k/.68u/.022u... and I allways have vol II at 2 aclock... can't do without it... we're getting close... well, in the right direction at least

Then perhaps it's the Normal channel that's getting the 10nF-12nF coupling cap since it retains the 820R/250uF cathode arrangement?

[N3m0 7h3 Fi5h]

1. Good Guest wrote:
Those chocolate brown caps can just as easily be .047uf's also.....the tone stack has the .022uf mustard types which would indicate the 2 changed caps were probably .022's originally...the .0022uf has also been changed ...could be anything from a 750pf like in the 5150 III ch.1 and 2 all the way up too a .0022uf...why change these stock coupling values? Unless you were changing the values?

The choc brown caps look like .047's ..I've seen .022's from that era and they are smaller. They could of been a lower rated vdc tho,can't remember...that's the big problem on looks alone ..different voltage ratings /different size.

A .047uf feeding the input of the phase inverter would add lows as described by one of the people who seen the innards...who said lows were added later in the circuit...the .047 feeding the phase inverter adds dramatic lows when you have greater than .022's in the power section...ie: .047's or .1's..if you have .022's in the power section the change is not dramatic.


That makes sence... but why would v1a's coupling cap be .047u? What would be gained from that?


More low frequency gain than a .022 ...you would have to experiment to hear..but it would explain Eddies statement that he likes his amp to sound like a stereo HiFi..here he would have extended low range gain on one ch.and if the other cap was a smaller value than the .0022 he would have extended high range gain on the other and mixed together it would be pretty HiFi sounding ...might be cool sounding with an effect jumpered thru it like some do with the echolplex.

There is also the risk that the ch. might sound muddy , but a lot of high gain amps have a .047 there and they usually follow it up with circuitry to filter out the lows right after leaving nice warm sustainy highs....then add the lows back later on in the amp.....it's a real science and the best thing to do is experiment.

http://forum.metroamp.com/viewtopic.php ... 2&p=383733" onclick="window.open(this.href);return false;



2. Strat78 wrote:
Very nice clip indeed!. Yeah, the 2,7k is interesting on V1b, I nearly fell out of my chair when I hit the first chord. Perhaps we have been doing this backwards. Get a nice fat tone early in the circuit, then dial in some more treble down the line. It helps with these tweaks if the amp is already fully broken in. I remember not liking the 2,7k when the amp was just off the bench. Anyway, lots more things to try. Oh, the 820 over the 2,7k was wild, tons of gain!


Hey Strat.
820 over 2,7k... do you mean in serie or parallel?
Where did you get that from? I remebrer seeing a post in the " Debate on Ed's plexi " thread, where vh junkie ( I think ) posted a schem for a mod in v1b; a 2,2k pot in serie with 820 to ground... that would mean having the pot on full you'd get just above 3k... Or do you mean in parallel? That would be araound 800 ohm ( ca )...

It was from this thread that I think you had a hand in. I have sence taken it out because it gave too much gain.

http://forum.metroamp.com/viewtopic.php ... 07&start=0" onclick="window.open(this.href);return false;

[Ralle]

We mustn't forget that the amp in that pic is not with the stock board... it looks like every component has been resoldered... so in my mind this is a pic of the amp way later than in the demo eara... and we all know that it was rebuilt after that...
But it's very interesting with that big choclate brown caps... the PI cap is for sure... but I have to look int that one for channell 1... I know I allways sue that vol pot at ca 2 aclock... maybe it does wonders with that combo...

[N3m0 7h3 Fi5h]

Good Guest also wrote:
...the .047 feeding the phase inverter adds dramatic lows when you have greater than .022's in the power section...ie: .047's or .1's..if you have .022's in the power section the change is not dramatic.

[Tone Slinger]

So Ralle, you have a .022 plate bypass cap on the bright channel, instead of a .0022 ?

[TJB]

That's would be my guess. That should put a little more lows in the lead channel, correct? Then possibly changing the 500pf on the 470k to 1000pf and also changing the .022uf on the PI to .047uf.
Hey T.S., the pic of that electrolytic at V2-A isn't clear enough to see the values to me. It could also be a .68uf but the thing that gets me is that the D.F. specs are saying (2) caps there but I only see (1).
Just by looking at the physical size of those large chocolate brown caps the .047uf would make sense but would an .022uf be that large too? I'm thinking a little smaller but would depend on the voltage rating.

[N3m0 7h3 Fi5h]

Hey T.S., the pic of that electrolytic at V2-A isn't clear enough to see the values to me. It could also be a .68uf but the thing that gets me is that the D.F. specs are saying (2) caps there but I only see (1).

You may find the answer, in the end of long post bellow..

http://forum.metroamp.com/viewtopic.php ... &start=570" onclick="window.open(this.href);return false;

Leadguy wrote:

1. In case we all start to forget, here is a John Suhr reminder

Trust me, I never cared that much about THE AMP but I did write the number in my book as being 12301 next to all the specific voltages and parts marked in all red pen along with "Ed's amp" as Ed stood by me and dialed it in with the variac (light dimmer) and the amp open. All of the red paint on the solder joints was original and untouched except for one added part up until the Treble pot which could indicate a master at one point. Also if it wasn't "the amp" why would Matt his tech contact me out of the blue about 5~6 years ago to ask if I had done a schematic since I was the last one to see "the Amp" in it's original state? I'm not obsessed about this amp since it takes a specific type of player to play it, it is not a friendly amp and you need authority and chops to make it sound right but as Marshalls of that era go it is definitely my favorite. Piss ass loud amp too even when variac'd. Ed was sincere with me, where he was fuzzy was what he had plugged in to the amp between his guitar and the amp. I'm not shitting anyone, the amp was VERY close to stock but were not the typical values you find in a GT schematic book, it had more gain (stock alternate values) and a tweak for more bass which also increased the gain which was the only non stock value. Anymore than that I cant say without their blessing. It also "sounds" to me like VH1 had the variac turned up even though Ed said it was always down and used for volume issues, basically turned it into a 50W and would also clip faster in the output section due to lack of headroom. Bias could have been wacked as well since he didn't adjust it when he demoed it to me.
__________________
John Suhr-President JS Technologies Inc - Suhr Guitars - CAA Amplifiers - CAE Cabinets

No ....I was looking at THE amp that Ed said to me "I used this exact amp for recording everything before F.U.C.K", It was not just a "stock Plexi", it was Ed's amp SL12301, I have the serial number written right on the old GT book page with my scribbles. The info I got from Ed I trust way more than Jose told me since what Jose told me was..... well very incorrect. I was referred to Jose by Bradshaw when I got my big rig and Jose loved Bradshaw since he sent a lot of work Jose's direction. When I quizzed Jose about Ed's setup he never told me anything about pedals just that it was his "mod" I was hearing into a nice plexi, I'm guessing he told different people different things. I've also worked on Framptons Jose and many others as well as made some duplicates for other people like Bob Rock after Jose was ill. So I am very familiar with Jose's work of which non of this was in Ed's favorite amp. Ed was trying to help out the guy who maintained his amps, there were no mods other than 1 that takes less time to do than it takes to open the chassis and certainly wasn't necessary for him to get his tone. Ed was working on an amp with Jose for years until near the end, it never got off the ground to sound the way Ed wanted it to sound. If Jose did gain mods on Ed's amps which I know is not true then it would have been a slam dunk easy thing to put on the market since it was already tried and true and tested.
__________________
John Suhr-President JS Technologies Inc - Suhr Guitars - CAA Amplifiers - CAE Cabinets

And Nitro.... about the year I saw it was probably very early 91, Bradshaw was doing his rig, fibbing to me or Bob would have been pissing in the wind, I also made him two modded Marshall he used for a crunchy clean tone, he used my prototype preamp on F.U album and then brought me the Marshall with Matt at Bradshaws shop while we were doing his rig. I used to be a solder inspector for the Military, it is very to see what parts of the amp were not original and were or were not original solder joints. The amp had not been mucked with except for few parts. To find out exactly what his signal chain was on the first album.... you might as well find try and find out how the universe got here since until Ed remembers exactly what he did, no one will know. They were just partying and playing, documenting what he used was the furthest thing from his mind... (his words)

Yeah except the peavey amp was not done yet and Ed didnt use it at all on F.U.C.K he used my preamp into Lukathers Marshall effects return I did for Luke while I was in NY and a SLO100 . He didn't use the same gear for recording as live. I was working on the preamp with Bradshaw in the early 90's, I sent the prototype preamp out before I moved out maybe 8~10 months earlier, I moved in early 1991 but did come out to CA to visit a few times before than. I worked on that Marshall after I moved out in early 91ish but he used the preamp prototype long before that. Ed's rig has been in the shop many times ! I do remember the Peaveys in his rig for live while I was working on his Marshalls at one point, It was there for updates all the time, I didn't pay much attention to that since that was Bobs deal. Not sure I understand what you are trying to say? Are you being passive aggressive here or calling me a liar? I wonder why I bother.
__________________
John Suhr-President JS Technologies Inc - Suhr Guitars - CAA Amplifiers - CAE Cabinets

I know when an amp has been modified
I know what original solder joints from Marshall look like
The amp was not modified beyond it's basic gain structure
Ed himself told me 2 feet from me to my face that the amp never had any kind of typical Jose mod in it. The 2 non typical parts in this amp contribute to the gain in a very minor way. They were not major parts and the amp Already had the 680n at the cathode of the cathode follower. It also makes less difference than you think when the amp is dimmed. Regardless of me being at the first recording session or not I also know my shit and I know what Ed told me. He was not clueless and knew the tweaks in the amp which again are very minor. See you guys in a few months. I have shit to do. A storm just took out our Internet (iphone tuping here) and am going for vacation so see you all in a few months maybe. And have fun chasing! Again I'm not desputing that Ed could have used a pedal of some sort. Just that this serial number amp never had any significant mods in it, Ed also told me it didn't
__________________
John Suhr-President JS Technologies Inc - Suhr Guitars - CAA Amplifiers - CAE Cabinets


"untouched except for filter caps and 1 added part which I prefer to keep to myself (Dave knows it well of course too). It is a very minor addition that Jose did giving it a slight bit more bass in the treble channel, when Ed demo'd the amp for me he dimmed every control. The circuit other than that was STOCK.... BUT !! it was not the every day Normal circuit, there were a few oddball parts that Marshall did use from time to time. Not every Marshall follows the schematics.

The 2 non typical parts in this amp contribute to the gain in a very minor way. They were not major parts and the amp Already had the 680n at the cathode of the cathode follower."


2. Ed's Plexi was 12301 and this is a 12267 Plexi

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
470pF mixer bypass cap
Bypass cap on V2a is .68uF
33k/556pF tone stack combo
47k NFB resistor at 4 ohm tap
220k bias splitter resistors
0.1 uF cap on presence control
47pf on PI


and mixing in the John Suhr (v2 fat cap and other mods)mods we get this from Dave Friedman

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
47pf on PI

When John Suhr saw the amp in 1991, it had a fat cap electrolyte (probably 470uf) in parallel with the stock .68uf on V2. Both the 470uf and .68uf were relaced by a 330uf electrolyte later on.

1991 is a long time after 1977 so take away the fat cap on v2 that John Suhr saw in 1991, and we get this

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
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
47pf on PI

3. Sorry for the long post...

[N3m0 7h3 Fi5h]

...

[TJB]

Thanks for posting that info!

[rgorke]

My take is that those pictures are probably from an amp Ed owns but not THE amp. None of us are Ed so we are not getting what he gets out of his instrument and the amp. We are left with switching components to match what we hear.

I have yet to hear a consistently closer tone than a straight '68-'69 spec as described in the Suhr and Friedman posts. The 330 cap, well for me is not make or break in terms of the core tone.

That being said, there ain't nothin' wrong with experimenting to achieve what works for you and your rig. For me, if I spent more time in the shed than in the shop, I'd be closer....

[jnew]

Some pretty definitive info right there fellas. I've always believed that there were no major mods to that plexi. But that amp on 10, a variac, EP-3, MXR and a furious pair of hands can modify any amp.

[julkke]

Ralle, what pick do you use?

[bobtec]