PTP board for a jmp MKII

[thelamehorse]

hello everyone I just bought a jmp mkII and the insides have been messed with pretty hard, all the caps have been changed to orange drops, so I want to get a ptp board in it and swap to sozos. I really like the way the mkIIs sound and wanted to keep that circuit in there. Which board should I get for it? Thanks a ton!

[demonufo]

The right one preferably!
Which JMP Mk II?
MV? NMV? 50W? 100W?

[thelamehorse]

Sorry, its a master volume, 50 watt. you can see in the photos it has a note that says its a model 1987 wired as a 2203. The chassis has 4 input holes in it and three square switch holes? Sorry for the phone photos. Thanks for takin a look at this guy.

[demonufo]

Oh dear. All those lovely original resistors replaced with cheap MF's as well. OK, you're right, lets's go down the PTP route shall we.
Except I can't find it in the store anymore! I know George sells them, I have one here!
Best drop Fido an e-mail I think.
50W Master Volume PTP board is what you need (2204)

I'm curious though, if yours has been rewired as a master volume, where on earth is the .68 cap 3rd from the left on the board?

[thelamehorse]

Do the jcm 800 boards work as they are so close? I guess if the 1987 pc board can be wired to a 2203 then the ptp board could work also? here is picture of the chassis on top of my marshall lead 20 turned 18watt. Thanks for the look.

[demonufo]

JCM boards are identical. But beware, the 1987 has actually been re-wired to 2204 specs not 2203. The 2203 is the 100watter, 2204 the 50.
There are a couple of components you'll need to change from the metro 2203 board.
Examine closely.

2203
http://metroamp.com/wiki/index.php/100_ ... lume_board" onclick="window.open(this.href);return false;

2204
http://metroamp.com/wiki/index.php/50_w ... lume_board" onclick="window.open(this.href);return false;

You'll notice some wiring differences too. Examine the diodes for instance. Orientation differs on two diodes, and the link at the bottom is not present on the 2204. Note the bias feed resistor should be 220K as opposed to the 2203's 27K
I actually thought there were more differences than that, but I suspect there are differences in feedback resistors on various layouts (and possibly wiring too)

Make sure you're wiring the amp from a 2204 layout, not a 2203.
I'd still email the store about the board though, I'm sure it's just an omission. I did mention it on a thread, but the admin seems to have ignored me.

[demonufo]

Oh yeah, just a thought. Unless somebody bought a new faceplate for it, that was never a 1987, as that faceplate is correct for the 2204 master volume, and the chassis' always had four holes regardless of which amp. Even early JCM800's can have 4 holes in the chassis on MV amps.
What model does the backplate state?

[thelamehorse]

The back says its a 50 watt master volume. Is the JMP 2204 circuit any different than the JCM 800 2204 circuit or is it just cosmetics? I thought the cap on the 1st stage is different but I couldn't see anything else?

[demonufo]

Just cosmetically different. The 2203 in the later JCM years (horizontal inputs) changed the number of filter caps, but the 50watters didn't change in between JMP and JCM.

[thelamehorse]

Just a couple more questions. I have the board from metro and I am close to done with wiring it up. I cant seem to figure out how the primary pt should be wired. Only the black wires out of the rainbow were joined on the circut board. And there is a purple wire off of the impedece selector i cannot figure out where it goes.

[thelamehorse]

ok, got the purple wire to the presence control. now the Pt here is a picture. do i just cap off all the other leads and have the black wires connect?

[demonufo]

Hmm, mine being a UK spec amp with a voltage selector, didn't have those wires going to the side of the board, so I just rebuilt that as it was. Also, it wouldn't have been a problem if I did though, as the board I bought from metro had all the turrets on the end of the board available to keep things wired as they were. (In my case though, they aren't in use)

Also, didn't have the original PT in mine, just a replacement Dagnall D2479, so I don't even know if the wiring would be the same colour coding. My other one (4104, combo version of 2204) is a mid 80's with a total different board layout and wiring yet again so that won't help.

I'd re-post asking for help in the Repairs, Restorations and Mods thread. Perhaps one of the big guns might chime in.

Respectfully though, (please don't be offended) I think I would have taken a look at George's instructions and started almost from scratch. Some of the pre-existing wiring in there is real sloppy.

I never did get any pics of mine finished (and it's been on loan for months now! ) but here is the links to the folder of pics just before I dropped the board in. With board pics too. I'm kind of disgusted how sloppy mine looks too, when I look back (bit of a pain in the arse perfectionist. I'm never pleased with my own work)
http://s255.photobucket.com/albums/hh15 ... 20Rebuild/" onclick="window.open(this.href);return false;
You'll notice I re-did a couple of wires with shielded cable in the first photo (looks like you're has this too).
Board had a complete set of mustards by the time I finished too.