Spartan good looks, I defy you to make a grab for the wrong knob on this device.
It was built with a hinging front that will allow access to the guts even while powered on. I love gear designed with an inherent trust of the operator such that they don't automatically conclude that the operator is an idiot that will likely kill themselves due to such a servicing convenience. You simply can't get away with that today... perhaps the people are actually honestly less intelligent?
Moving to the rear, we see your typical back mounted tube and transformer set. Note pre-UREI label of manufacture. I do believe "Studio Electronics" was a Bill Putnam endeavor however, this unit appears to be a rev 2, with HA-100X input transformer and compressor/limit switch and T4A designator. As you can plainly see, the T4 opto slot is populated by something decidedly homebrew (thanks to my uncle for the opto build, and the unit). I have fuzzed out the serial number, which is low four digits.
I've always preferred everything in duplicate, being fixated on stereo. Having kept a loose eye on the going rate of complimentary UTC HA-100X transformers, I am planning instead to build a clone utilizing something I already have in the input iron pile, hopefully I can come close, I'm sure I can achieve 'useful'. Looks like a 50th week of 1964 to me, indicating they were running through existing stock on their way to rev #3, A-10 inputs.
Here's a shot of what's going on inside the current opto element, simply a switched VTL5C4/2 allowing for fast/slow decay. I'm planning on rolling a closer to stock arrangement with luminescent panel coupled with photoconductive cells when I get a chance. I did have to assert focus to avoid trying to dig up the box with old stock photocells in it while moving stuff from the old storage set-up to the new room. They are there, somewhere, and perhaps some of them will come close to operating within the range of the original Clairex CL505L elements used in the T4A & B (so far as I can tell).
Spec attached, for what it's worth.
I do plan on recapping this, as it appears that everything is original. However, my replacement frenzy will NOT include these, only the electrolytics. Frankly, having recalled mica "dominoes" inside, I was a bit dismayed that they are not in the signal path. Oh well, at least it will contain enough carbon comp resistors to convince most electrical engineers that I am a mindless savage.
Pretty neat layout, and the relatively low parts count makes for a nice wide open layout. I believe the part at left is a variable mica capacitor, the Aerovox center appear to be date coded 20th week of 1966, the domino cap at right is across the "FLAT" trimpot, indicating it may have a say on overall frequency curves and as such is probably carrying a bit of signal. Well, I can rest easier.
Continuing on the datecode front, the UTC A-24 output transformer looks coded 44th week of 1966.
The Sprague 40-40-30-30@450 can cap is dated 4th week of 1967, pretty sure that one needs to go. I'll probably slap a new production CE Manufacturing twist-lock at 40-40-20-20 and make up the 10uf internally if the 20s cause problems, which I doubt.
28th week of 1968 seems as close to build date (without going over) as I can get. I'd say late 1968 origin, since I haven't been able to find a serial number to date of manufacture cross reference.
This is for you, Nigel Tufnel.