Another 'ultimate marshall' build

[Thiez]

Since i couldn't find a seperate topic for introducing myself i'll start of by introducing myself here.
I'm Thijs, 23 years old, studied mechanics and electrics and obsessed with music, aswel playing aswel listening to it.
I've build a lot of fx pedals over the time and two years ago i tought it was time for something more challenging. A started building a tubeamp. The amp was an AX84 P1 build, but since it was a learning project for me and i used other transformers etc. i changed a lot of values to make the amp work fine. I studied the book 'building preamps' from mr. blencow. and get the theory quiet good.

SOOOOO, it's time for a new challenge!. And it's gonna be a big one.. Lot's of people build an ultimate marshall in there eyes. So that's why my topic says 'another'. So here's my version of the ultimate marshall:

- plexi normal and bright channel
- extra tube to switch the bright channel into jcm800 (with standard MV to get an even level with the plexi)
- switchable Jose master
- PPIMV
- FXloop

Footswitch that can switch plexi/JCM800 and add the jose master clipping.

I'll put in an extra tube and only using one gainstage of it, so i still have on stage left. Any suggestions? (have to keep in mind that my transformer is a standard 1987 drake.)

I'll start of with a standaard 1987 build (with the added tube and board space etc installed) and if that works i'm gonna put in the next part and test it again.

[Thiez]

Here's the schematic so far.

http://dl.dropbox.com/u/19886483/supaplex.pdf" onclick="window.open(this.href);return false;

Have to add the relais part etc for switching and the effectloop. Probably gonna add a few screengrids on the powertubes aswell.
The anode resistor over third gainstage will be removed. That was because of the 300k resistor in early MV model of marshall, but anode resistor switching is gonna pop and i don't want any pops.

[Thiez]

Allright, the headshell is done. This weekend i'm gonna bend the chassis. Meanwhile i''m bussy putting the schematic into a layout. It''s gonna be a PTP offcourse.

Not a lot of replies here yet. Maybe the project is to basic for this forum haha. Probably it''s because i''m new here. But i hope you guys can enjoy this build.

Here''s a picture of the headshell, it was to big to post so it''s a link.
https://fbcdn-sphotos-a.akamaihd.net/hp ... 4261_n.jpg" onclick="window.open(this.href);return false;

[frenchie]

Not a lot of replies here yet. Maybe the project is to basic for this forum haha. Probably it''s because i''m new here. But i hope you guys can enjoy this build.

it's because you posted a schematic of a jose master , it's a big time taboo here dontcha know .... now you deserve to die all alone ... kidding , nice project indeed , and superb headshell so far ... however my stupid question comes ..beware ... in the v3 plate resistor 100K+220k network why didn't you just put the 220k directy on the switch to take it out of the circuit instead of making a switchable "wire bypass" like you did ?? any advantage by doing so ?

[Thiez]

Haha Allright, i will call it a diode clipping master volume. Then everything will be allright and we can all live together in happyness right?

About the anode resistor. The voltage on that site of the tube probably gonna give me a popping noise. I installed it this way the first time and leaved it there without any changes cause i'm not sure if i will put it in the amp...
I can also put a 330K resistor in and switch a resistor parallel to it, to make it 100K.
But like i said, not sure if it's gonna stay because of the popping noise. I was curious how it would sound, cause it's done in the early MV amps and it's gonna give a litte more gain.

[Homebelly]

I'm tagging on because this is a type of build that i have been working toward for a while now.

I'm also interested in who made your head shell?

PM me if you want to share.

[Thiez]

I won't have to pm about that, because i made it myself. If i'm building something, i'm doing it all by myself haha
The headshell is made of 18mm multiplex (instead of 15mm used by marshall i tought), the chassis gonna be made of aluminium and will be done this weekend (pictures will come) and the faceplates are mad of brushed RVS304 heated in an oven to make it collor yellow/goldish.

[jimmyride]

The headshell looks awesome indeed. I'm in desperate need of one as well. Do you have a blueprint for it? Or is there one somewhere on the net? I tried hard to find it with no succes.

[Thiez]

I don't have any blueprints of it. it also isn''t a 1:1 clone of a marshall. The dimensions of mine are a bit different. 710(w)x260(h)x240(d) and then 18mm multiplex, i did this to fit it in to the flightcase i allready have.

[robnoxious1]

Man that headbox looks great.

[Thiez]

The schematic is done. So i started the layout of the amp. Now i used more of a soldano/bogner kinda layout. But i was thinking about noise, won't it give me noise when i put the AC heater voltage wiring underneath my pots in front of the amp?
The heater wires can go underneath the pots or under the PTP board.

Here's the layout so far:
http://db.tt/ctaZXvZm" onclick="window.open(this.href);return false;

Edit: the layout isn''t done, so i know there are a lot of loose points

[Thiez]

Allright, screenresistor and gridresistor. Like you may have seen in my schematic i have non of them. The schematic of Joe Piazza has non. But, some schematics have, some schematics have no resistors.

The 1K screenresistor is to secure them for high gridcurrents, so just a safety reason. Do they have influence on sound?

Then there is the gridresistor. Again on the schematic of the 1987 there is none. Marshall used 5K6 often for the later plexi's and JCM800. This is to prevent oscilation. The highter the resistor value the more high end rolled of if i'm not mistaken? So is this resistor needed or can i go with a smaller value or no resistor at all?

Hope to get some replies

[toner]

I would definitely use grid resistors because they will have no effect on tone/feel. They can only help by reducing very high frequencies (RF) and possible oscillation. 5k6 is common.

I'm not sure about the effects on tone/feel of screen resistors. They obviously limit voltage and current to the screens to help protect the tubes (especially current production). I've read a few accounts from people preferring to not use them but I have no first-hand experience with that.

[Thiez]

Thanks for the reply toner. I will use grid resistors and i think i will install the screen resistors as well. Don't like melting tubes haha. Maybe i'll try with and without, to see if there is a difference.

[Thiez]

Another question here. I was looking at the channel switching to the JCM800. I drawn the switch at the anode of V1. But this is place had got high voltage, so it's better to switch after the coupling cap offcourse. But JCM800 and Plexi schematic both have other valvues of coupling cap.
Now my tought was to put the 22nF cap on the anode, then the switch (so the JCM800 22nF coupling cap is there) and then put a 2.2nF cap on the plexi side of the switch. The replacement value of the caps is then 2nF so comes close to the value of a plexi coupling cap.
But i don't know if two caps in series as coupling gonne give me any trouble? Maybe with phasing or something? Somebody that can tell me something about this? Or have an other problemsolver?