76 or 77 JMP???

[Diezeldale]

Good idea, but it will be impossible to find a faceplate for a rocker switch amp with a polarity rocker.
To be fair, they're unsafe anyway, so best omitted IMO. Or at least, NOT wired up.

Ive heard some horror stories about the Polarity, I will have it checked out and maybe go ahead and install a grounded three prong. This aint no 68' Plexi, for $355 cosmetics dont matter, I actually like the Rugged look to the headshell, throw in some chicken head knobs and a Friedman Brown Eye MOD with the SAT switch and this baby will Crush the JMP competition! Maybe I can have the white Polarity engage the SAT???

 

[Diezeldale]

We'll the 76/77 mystery may be solved! Amp arrived today and just from my initial inspection I see the Serial number on the back is SL/A 7200H making it a 1976 Head, the front panel is a custom add on. I can see the original plate is still there behind the fake front and my be in original condition, the Ohmn selector plug is missing and a fuse is missing. Other than that it' may just need some TLC, more to follow after dinner.

 

[Diezeldale]

For the money, anything even approaching a 2203/2204 that works is a big result.

Here are some gut shot of the 1976/77 Marshall (SER # 7200H)

 

[Diezeldale]

For the money, anything even approaching a 2203/2204 that works is a big result.

Here are some gut shot of the 1976/77 Marshall (SER # 7200H)

 

[demonufo]

Well, whaddya know. Inside it's all stock, except for the changed resistors required for running 6550's. Result.

I assume the OT tap must have been hardwired since the selector is missing. This wants rectifying. (Since the original value is toast you might want to fit a modern switch instead which is safer that the original push in style).

 

[Diezeldale]

Well, whaddya know. Inside it's all stock, except for the changed resistors required for running 6550's. Result.

I assume the OT tap must have been hardwired since the selector is missing. This wants rectifying. (Since the original value is toast you might want to fit a modern switch instead which is safer that the original push in style).

Yes sir, it needs some TLC, but for the most part it's little stuff. In the mid 70's didnt Marshall ship US market amps Stock with 6550 tubes? I think these might even be the Original tube's since the amp was built, these old ServiceMaster welded plate 6550's with a matching trio of 12ax7 look like they have been in this amp since day one, they prolly shot but cool to find these in there.

 

[demonufo]

Yes sir, it needs some TLC, but for the most part it's little stuff. In the mid 70's didnt Marshall ship US market amps Stock with 6550 tubes? I think these might even be the Original tube's since the amp was built, these old ServiceMaster welded plate 6550's with a matching trio of 12ax7 look like they have been in this amp since day one, they prolly shot but cool to find these in there.

They did, yes, but the resistors in yours have been changed. Perhaps somebody changed to EL34's and back to 6550's??
The soldering on the resistors is sloppy and certainly not stock (it even looks like the original resistors may have been cut, and these soldered onto the originals legs).

The resistors appear to be Beyschlags of roughly the right period though (before anybody says Beyschlags were red, Beyschlag made a LOT of different models, and were most certainly NOT all red), so they are fairly old at least.

A quick recap and you're hot to trot. Maybe a headcab from Mojo wouldn't go amiss, but that looks to be a major bargain, despite the outside molestation.

 

[rockstah]

its a good deal for 76 for sure and yes i agree its probably been back and forth from 6550 to el34's back to 6550's. i have worked on a few of these. nice amps.
Mark

 

[demonufo]

I didn't even notice the serial number (well spotted Mark).

It is for certain a '76 (actually the green dip caps give this away as well) and would NOT have had rocker switches from new. It would have had Arrow branded plastic toggles, exactly like my 2204 (which had an identical complement of components on the PCB, save for the slight difference between the 2203 and 2204, just before I ripped it's guts out and rebuilt it).
This would explain the confusion about the headcab styling anyway, at least.

 

[Diezeldale]

its a good deal for 76 for sure and yes i agree its probably been back and forth from 6550 to el34's back to 6550's. i have worked on a few of these. nice amps.
Mark

So Mark, would this be a potential candidate for a ROCKSTAH MOD 5? I bought this amp with the intent getting another amp MoD, I was looking for as old as Marshall I could find for the purpose of a hot rod Marshall, I have Friedman Moded Marshall 50watt (BE/HBE/C45/FAT/SAT/EFX)and Im looking for another amp in the stable. I seen this listed as amp parts of Ebay and rolled the dice, I think it has great potential, What's a MOD 5 with effects loop cost?

 

[Diezeldale]

I didn't even notice the serial number (well spotted Mark).

It is for certain a '76 (actually the green dip caps give this away as well) and would NOT have had rocker switches from new. It would have had Arrow branded plastic toggles, exactly like my 2204 (which had an identical complement of components on the PCB, save for the slight difference between the 2203 and 2204, just before I ripped it's guts out and rebuilt it).
This would explain the confusion about the headcab styling anyway, at least.

I'm not a Marshall expert like some of you, but I have played Marshall amps since about 1982 and have hade at least a 12 or more JMP's, JCM's and others over the years. But I will have to question your expertise on this amp not being a rocker switch from new, I have a pic of the Rockers from inside of the chasis and see no sign of post production mods for Rocker switch, this wouldnt be as easy as drilling a hole and putting a switch in, the spacing of the old style arrow branded pastic toggles compared to adding three rockers would leave a trace or sign of change if they line up at all. anyone know the spacing specs and the process other than factory cutting perfect squares for a replacement set of rockers?I also have pics from the AmpArchives of a 1976 2203 with Rockers? Not that it matters, this aint no 68 plexi on the floor of Sothbys auction house, it's a fleabay amp purchased for the sole purpose of a MOD, but my analysis shows this chasis at least to be stock. Again Im not throwing mud here, I respect the and thank the input from the senior members and resident experts, but all indicators show it is stock from 1976 with Rockers!

 

[demonufo]

Hmm, it appears you are correct. Difference between the sides of the Atlantic I guess. I see quite a few 2203's and 2204's from 1976 now that I actually look, but only US models with hard wired mains cable, and no voltage selector.
UK examples of rocker switches don't seem to come in until at least late Feb '77/early March.

However, I have still seen one US example with toggles from Feb '77 that I am certain was not Canadian or Swedish (didn't have the extra complement of fuses and did still have a 16ohm tap), yet the toggles were metal.

Marshall timelines have been known to blur. I guess occasionally when you have a massive inventory of parts, some turn up at random.

I always found it amusing that some of the earliest JCM800 models had JMP rearplates fitted.

Now, the question is, what the hell is going on with those switches. Looks like an accident waiting to happen. I'd be tempted to find a layout and return that amp to proper 2 switch wiring, and maybe utilise that other rocker for a alternate tonestack, or a cathode bypass, or maybe even just another cathode resistor in parallel as a gain boost.

 

[Diezeldale]

Now, the question is, what the hell is going on with those switches. Looks like an accident waiting to happen. I'd be tempted to find a layout and return that amp to proper 2 switch wiring, and maybe utilise that other rocker for a alternate tonestack, or a cathode bypass, or maybe even just another cathode resistor in parallel as a gain boost.[/QUOTE]

Thanks UFO, This old beast will have to receive serious attention by my local Vintage AMP tech. I will have all the wiring inspected thouroughly before I attempt to plug in, looks like the Polarity switch may have been disconnected? Im alrady online ordering a new Ohmn selector, Fuse caps, Tubes. it Needs a cap job and Im sure tubes, sockets, pots and plugs will get inspected and cleaned. Ahh I love this addiction in search of tone! Then I have to find where to go for a John Sykes / High Gain Jose Mod, I have a Friedman Kitchen Sink Mod, maybe just the BE/HBE for this Beast!

 

[rockstah]

hmmm

 

[Diezeldale]

hmmm

Yes Mark this was intended to get your interest, I'm looking for a MOD specialist to help me get where I want to go with this amp. Once I get it cleaned up I'm looking for a mod, something that can go from AFD to J.Sykes/Jose territory? any Ideas?