New member with mystery 210-65

Hello All,

G'day, I'm new to the forum, thanks for having me.  I'm an Australian valve amp enthusiast and part-time repair tech and have a customer's 210-65 in for a service and re-tube. It's the first MM amp I've worked on, and it seems to be a bit unusual.  I'm asking for some help identifying exactly what this one is (export? special order? domestic US that's been modded?) as well as some advice or re-assurance on the service work I'm about to do, please?  I've been encouraged by @mm210 who I met at a different forum to share some pics and info here.

I'll describe what I've got first, and post a bunch of pics at the end. Apologies in advance, because this will be a lengthy post.

It's the 12AX7 version, with 2275-65 chassis no. placard on the inside of the chassis. There is no serial number anywhere on the amp. All transformers appear original with 1975/76 date codes and 606 manufacturer code. Original Sylvania EL34's and a pristine-looking Zaerix 12AX7.  All filter caps are original with 1976 date codes on the big ones.

The amp runs on 240V/50Hz mains, but the rear panel placards, and US-style output socket (which is still connected @ 240V) all say 117V/60Hz.  The .047uF 'Death' cap has been removed but ground switch still has mains voltage connected to one side.

The PT is stamped 1-65 but has an old (probably OEM) label stuck to it inside the chassis with "No. 5" hand-written on it and "5" written in sharpie pen on the chassis next to the PT. The primary winding wires on the PT don't seem to match the 2275-65 schematic, and the amp doesn't have a low-power function. The (broken, 250V-rated) DPDT high-low-off switch is only connected on one side (high) and the neutral mains wire is connected directly to the PT wiring (instead of also being switched as per the Australian standard and all other vintage 'export' amps I've encountered). 

There is evidence of a few component changes/mods  (caps & resistors) on the pre-amp board and vol-pot, and two Op-Amps that differ from the schematic (they're LM307T, not LM307H).  Other than that, and the unusual power switch and primary PT wiring, the amp appears largely un-molested.

The amp belonged to an Australian pro guitarist (RIP), who I'm fairly sure did some tours in the USA in the early1980's.  It was acquired by my customer about 15 years ago. My customer was a guitar student of the former pro-guitarist owner and had been playing through the amp at lessons since the mid-late 1990's. Prior to that I have no known history on the amp.

The amp powers on, and sounds fantastic, but does have a lot of hiss and hum and the tremelo isn't working with or without a footswitch or shorting plug.  I'm about to replace all 9x electrolytic caps,  re-tube and re-bias (cooler than MM service-bulletin spec). I'll also be changing some corroded input jacks, all 2W power-supply resistors, and will put a new 10ohm resistor to ground on each EL34 socket instead of the one shared between both.  If the tremolo doesn't come back to life after that, I'll play with the trem-bias pot and then replace one or both trem FETs.  I'll be replacing the power switch so that active and neutral are both switched. Anything else you MM gurus recommend I do as a starting point?  Do the rectifier diodes and zeners fail often? 

Thanks for reading through to here, and for any help, info or advice you can offer,

Scott

Now for the pics...   I'll post a bunch in subsequent messages too, so I don't exceed the site's file size limit...