Hey ddt, no worries, others hear may know more  .  So according to the MDRT instructions, not changing the resistor on the tube board (R9) to 300k will mean the high voltage will stay at 190Vdc and not achieve the desired increase, in this case to 220Vdc and for the MDRT 240Vdc.  However, some may prefer it that way?  SC for example likes his MP-1 stock as he prefers the sound.  He even went so far as to source a very early original MP-1 transformer as ADA did change them a bit in later units, probably when they changed the rear jack to inst level and got rid of the inst/line level top switch and went to v2.x firmware.  The increase in high voltage provides for more dynamic range and opens up the sound.  SC preferred the original tone/sound and, in some ways, I agree with him.

Fantastic! Thank you so much for the info.
Looks like the R9 240k resistor remained in place in this MP-1, so basically it's unfinished business. 

Hey ddt, that looks like a custom transformer.  The stock tranny is one bobbin not 2 like the one in the pic.  Also those specs (12V heater, 220Vdc high voltage) are very similar to the MDRT (12.6V heater, 240Vdc high voltage).  The original trannys are 8-9V heater and 190Vdc high voltage (see MJMPs site https://www.marshalljmpmodshop.net/miscellaneous_parts_and_replacement_tubes.htm).  The MDRT is 2 bobbins but side by side. I'm sure there are other mods and custom transformers around, IIRC Rob Hell was getting some made quite a while ago (I think in China). 

As far as I know, ADA never made anything like it.  My guess is it's been modded with a custom transformer and should sound and perform much like the MDRT.  There should also be a 300k resistor on the tube board to accommodate the increase in high voltage (see attached for location).

Hey Harley, an option for using it in a loop would be combine it with your MP-2.  As the MP-2 stereo parallel loop is just before the cab sim outs, it's very similar (if not slightly better for recording) to a standard 4CM.  But then you have other rack FX you can use that way  . 

I saw some soft rack thingys a while ago and thought about a 2 RU with MP-2 plus rack FX unit.  Then you just need either a stereo amp set up for live or plug cab sim outs into a desk (or both).  A bit bigger and heavier than where you are going with the GP-10, MP-2s have a bit of weight to them, but with a shoulder strap it would be like a big laptop and be carry on on a plane.  Although you'd still need a lead bag or some such for the midi pedal etc.

The last session I did I just took my 4 RU MP-2 rack (MP-2, Midiverb 4 (in MP-2 loop) and B200s).  I didn't need the power amp and just went into the desk with the cab sim XLR outs.  I also have a small suit case thingy (like every one uses on planes) for my MXC, expression pedal and leads.  I even manage to fit one of those small folding guitar stands in it. 

It will be interesting to see how you go when you deep dive into the editing.  From the review I watched, his main apprehension for using The GP-10 live was it has no banks and you can only go up or down with the patch selection.

Hey Harley, well it would be great if you can tune it to do both, it's allot of sound(s) in a small and light box.

Richard, I can have it do both, I just need to use a real amp with the guitar part of the overall sound. There are still a few other cabling ideas I want to try though. I want to try this  in a 4CM set up, then there is the option of trying it in the loop for the effects only, (not including the synth portions of the sound). It's kind of a neat thing to mess around with at home, but I still need to take a deep dive into the editing and see what I can do with it.

Y'know, the last time I was in the studio (who knows, maybe the last time I'll record), it took a good half hour to dial in our other guitarists' Line6 pedal board that he runs directly into the PA. It took 2 minutes to dial in my Peavey Classic 20mh.

20 watts of fury beats 128 patches of modeling

Nothing beats real amplifiers. That was never in question. The real question with this particular pedal was would it be good enough to gig without an amp? So far, I'm not hearing it that way.

I'm puzzled. I've come across an ADA MP-1 board revision "E" from year 1989 with the stock looking transformer, which gives over 12V of heater voltage and ~220V of voltage feeding the tube board. It has been modded with 5 Ohm / 5W resistor to step down the voltage for the digital section's voltage regulator input.

The question is, was there anything like that either officially or custom made by A/DA back in time or was this modded by a shop? Does anyone know?

https://drive.google.com/file/d/16vkYGij3qYmDgdfbmqpMB0Efbem4BeGj/view?usp=sharing

So update from MikeB, obviously the wooden skewer fix isn't particularly robust, apparently it managed the first move/relocation but not the next  .   
 
Some bits he told me: 
The cable at the front panel end (which you can't really get into) is part of the membrane switches (based on other membrane switch construction he researched) so you can't replace it. 
The socket on the PCB is old school (of course) and not used any more (he hasn't found one yet), moreover, they are only good for up to 10 insertions/removals.  So don't pull it out unless you HAVE to.  Probably I accidentally pulled it out when I changed the display? it's a long time ago.  It's easy to dislodge when you change the display as the display connector cable runs under it. 
It seems trying to clean the exposed ends (very thin silver allegedly) of the ribbon cable seemed to do more harm than good.  Apparently he spent quite a while carefully exposing some clean trace x 10 with a razor blade.  Very fiddly no doubt, but he got there.   

Next step is remove the PCB socket and attempt to repair it, i.e. bend the individual contacts so they "get a grip" as it were.  He thinks they maybe can be removed individually, squeezed and re-inserted?

Hey Harley, well it would be great if you can tune it to do both, it's allot of sound(s) in a small and light box.

Y'know, the last time I was in the studio (who knows, maybe the last time I'll record), it took a good half hour to dial in our other guitarists' Line6 pedal board that he runs directly into the PA. It took 2 minutes to dial in my Peavey Classic 20mh.

20 watts of fury beats 128 patches of modeling