My Rockstah Mod 5 2204 guts...

[Tone Slinger]

I 'think' I recall that Erics didnt have a v2a bypass cap. I know for certain that one of Marks Mod5's didnt. It was a Youtube vid about 2 or 3 yrs ago. It was called something like '!984 tone' or somethin. The audio indeed sound pretty '1984ish' 'House Of Pain', etc. There were lots of amp pics both inside the headbox and out. One real good board shot. That video was edited and eventually took down if I'm not mistaken. At that time,Mark was seriously NOT wanting to totally give out his spec. I thought Mark probably asked him to take the pics out.

[AndyK]

Hmmm. If Mark decided not to add it, maybe it was based on what he was hearing on tha particular amp?

What would adding it do I the tone?

[efraser68]

My JCM 800 has changed hands a few times. First sold it to a friend here (Ender) and then it changed hands over to Popskull.

[AndyK]

My JCM 800 has changed hands a few times. First sold it to a friend here (Ender) and then it changed hands over to Popskull.

Just curious, why did you wind up selling it?

[efraser68]

There was nothing wrong with the amp really. I was coming from a JCM 2000 DSL prior to that amp so that was my frame of reference. But once I had a chance to play a 12xxx series, no cascade, my ears and hands said I must have it. I was willing to take the trade offs of the Master Vol convenience to have an amp that feels 'authentic' for lack of a better description. Mark sent me a few messages not too long before his passing saying he "knew I would someday come back to his M5" and of course in a perfect world, I'd would love to have both.

[AndyK]

There was nothing wrong with the amp really. I was coming from a JCM 2000 DSL prior to that amp so that was my frame of reference. But once I had a chance to play a 12xxx series, no cascade, my ears and hands said I must have it. I was willing to take the trade offs of the Master Vol convenience to have an amp that feels 'authentic' for lack of a better description. Mark sent me a few messages not too long before his passing saying he "knew I would someday come back to his M5" and of course in a perfect world, I'd would love to have both.

I hear ya. I sold my original Rockstah modded 1959, to scale back to this Rockstah modded 50 watter. I've thought of selling it for more natural Plexi tone, but always would regret it, so I'm sticking with it.

With a 12xxx series Plexi, if you put a LARMAR PPIMV in, without cascading the channels, will it sound/feel like a Plexi still?

[Tone Slinger]

It was Eric's clips of his Mod5 JCM800 that made me want to try it.That Jcm800 1987 is the ONE Rockstah modded amp that can pretty much be verified by its various scuffs and stuff. Its been on at least 3 or 4 Youtube vids (2 by Rockstah Amps),so that is one of the few that I think can 100% be proven to be Marks work.
The bypass cap on v2a doesnt affect things as much as the one on v1b. That .68uf/2.7k (v1b) combo is in ALL Marshall 1959,1987,2203,2204 circuits,and is what Mark always left it at or used. On v2a, a cap over the cathode resistor (820) will slightly boost the gain in certain frequencies, depending on the caps value. Larger values lets in less highs (appears as more bass),lower values lets in more highs (appears as less bass).The lone unbypassed 820 there seems a little more stable and firm imo, so if an amp doesnt need any help, that resistor should remain unbypassed.

[stef]

Hmmm. If Mark decided not to add it, maybe it was based on what he was hearing on tha particular amp?

The reality is that installing (properly - not via piggybacking) a capacitor in a PCB amp is time consuming. Drilling 2 small holes very carefully and very precisely across 820r and then placing and soldering a cap is PITA, but possible - I did it in my amp flawlessly.
If that's true what TS pointed out about Eric's and some other amps, then I think is safe to presume that he did not add anything on V2a when he worked on PCB amps in general.. The PI coupers, mixer, NFB and everything else is left "stock", the only exception is the V1b (or in this case V1a) coupling cap - the "infamous" xicon 2n2 + PPIMV = Mod5 (PCB amps)
His own builds do have slightly different "Mod5" specs (mixer, cap on V2a, NFB, PI)

[Tone Slinger]

Does a 12xxx with a ppimv sound and feel like a dimed plexi ? Only if you have the ppimv up so high that its nearly out of the circuit. At lower settings NO ppimv circuit I've encountered sounds like a dimed Super Lead. In other words,no form of volume attenuation or 'scaling' can do what a roaring dimed non master volume Marshall can, from a point of pure tone and dynamics. Some power attenuators (Aracom for instance) can be brought down a bit more than others, but in general, half attenuation is the MOST amount you would want to use before you completely miss the intended target, tone-wise.
Having said that, output tube distortion isnt for everybody, so then you think "How do I get the best of both worlds", incorporating aspects of distortion and ease of use in one easy to use top. I think that for single channel amps, that the Mod5 spec and the Bray Mod1 are good choices.

[stef]

,

[stef]

Does a 12xxx with a ppimv sound and feel like a dimed plexi ? Only if you have the ppimv up so high that its nearly out of the circuit.

Believe it or not my amp (12xxx specs) did not sound the same even with the PPIMV on 10, only when I completely removed it the true "plexi" tone came back. In theory it should be out of the circuit, in reality it's right there if you can see it inside the amp
Sounded awful below 7 on the dial (PPIMV)

[AndyK]

Does a 12xxx with a ppimv sound and feel like a dimed plexi ? Only if you have the ppimv up so high that its nearly out of the circuit.

Believe it or not my amp (12xxx specs) did not sound the same even with the PPIMV on 10, only when I completely removed it the true "plexi" tone came back. In theory it should be out of the circuit, in reality it's right there if you can see it inside the amp
Sounded awful below 7 on the dial (PPIMV)

Interesting. I guess relatively, the PPIMV sounds better than the usual master found on the stock 2203 - but still kills the tone compared to the stock Plexi circuit.

You really can't get around the fact that non master volume Marshalls sound their best stock, and super loud.

[mightymike]

I never saw him use the PEC pots either. You never know though.

Mark's build

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http://www.mediafire.com/view/?opu03b9f3zi9a09" onclick="window.open(this.href);return false;
http://www.mediafire.com/view/?dhde99kzafh7th7" onclick="window.open(this.href);return false;

If thats Marks, then there ya go. funny thing about that one is they are all PEC pots.

Like I said. You never know.

This amp was Mark's first 12000. I know because I drew the intial layout for him, and helped him. If you notice it's Aluminum Chassis like mine. This was built before George had 12000 kits and steel chassis. He initialy built it w I th M e r r e n tranny but changed them. This was the amp that he first put his mod 5 spec on. Any further doubts? I have a pic with his signature on this amp's chassis. Flames can confirm this amp as well, because Mark had him repair it.

As far a I know this was his main amp, unless he later sold it an made the 79 it. Just now that the EVH tone right here thread is this amp. If he changed it since... Probably

[mightymike]

Also realize that if someone sends a rats nest looking amp to be repaired or modded, we will do the mod or repair, but cleanup is extra. Using Mil spec and mustard on his personal doesn't mean he will use it on everyone. Point being: The amp from the OP could be the real deal.

[Tone Slinger]

Just wanted to add that these mid to late '80's Jcm 800 2204's (not the 2203's) had higher preamp voltages, as compared to the one's from the earlier '80's (basically the 'main' difference between vertical and Horizontal input models). In the gut shot pics of this amp of AndyK's, you can plainly see that another 2 watt resistor (probably a 10k ohmite) was added to go with the stock 10k that was there (The 'voltage drop' resistor right to the left of the PI section). This reduces the preamps voltage, which makes a significant difference. So, based on that, I'd say that Mark most definately had his mitts in this one. Not many people know of this preamp voltage discrepency in the horizontal input 2204's.