Help identifying mystery RCA board with Melcor opamps, UTC A24 and T4A Cell!

[orangechili]

I would love to get some more info on this board I just acquired! My best guess is its out of a 60's RCA custom console from the master buss section....

It has
-UTC A24 transformer(possible input TX)
-2 Melcor 1731 opamps
-interesting T4A looking device with clairex 505L photocells
-4 RCA transistors on board as well

I have no schematic or info on the board. I figured it was some kind of compressor board when I got it but upon further inspection under the metal can I found the T4A looking device and that got me thinking. Is this an early attempt by RCA designers to transistorize the LA2a circuit? Possibly before the LA3a came out?  The controls for Gain and Peak Reduction are trimpots next to the opamps on this board. Any info or opinions on this greatly appreciated. I'd love to figure out this board's story

 

[orangechili]

Picture of inside metal can of T4A looking unit, the bottom of this has 5 pins in a straight row, no octal socket...

 

[pucho812]

I serviced an rac console earlier this year that happens to be right down the road and is  the same model found in the country music hall of fame in nashville that came from RCA studio B,  I don't recall seeing any of those modules in it. I have a ton of photos I should post, maybe I did post them. But the console is made up of the uoab(universal  operational amplifier board)  which is the core componant used for summing, sends, returns, preamps, etc. Then the desk had melcor 2 band eq's and cl-20 compressors in it.  Unless that is in a cl-20 I have not seen that board before. 

 

[emrr]

If it were from an RCA board, the 1731's would be branded RCA, wouldn't say MELCOR anywhere.  The RCA pcb's never have transformers mounted on them either.  I've never seen this board before.

 

[orangechili]

Interesting, the 4 transistors are RCA branded if that helps in identifying it. I believe I have seen some earlier RCA boards that had melcor branded opamps on them but I could be mistaken.

 

[orangechili]

Another picture of the unit, it is a unique design from what I see

 

[orangechili]

I think the UTC A24 may be being used as an interstage transformer of sorts here instead of an input transformer to drive the EL panel in the T4 device. That may explain why its mounted to the board? There is  numbers on the bottom of the board if that helps at all: 791806

 

[emrr]

RCA made transistors, means nothing.

Even if RCA used it as an interstage transformer, they rarely mounted transformers to a PCB, and when they did they were much smaller transformers than this. 

This may be.....a Melcor product! 

 

[orangechili]

Gotcha I'm just trying to figure out what it is. I have seen nothing online for it, i'm wondering if its a prototype that never took off of sorts. There are some mojo parts here for sure.

 

[sasquatch]

US Navy contract ?

AN/GSA-33

Gary

 

[emrr]

Looks different

 

[orangechili]

From what I see online on the old melcor stuff it looks like they did mostly custom consoles/units so it may be hard to know for sure... It looks like an La3a with opamps to replace some of the transistors

 

[CJ]

all you need is an A-10 and you have the makings for a way cool retro LA2,

oh, and a pair or API pre amps, great score!  ;D

where did you get it?

 

[orangechili]

On fleabay randomly searching La2a iron. I didn't even think too hard about the other components till it showed up. I figured it was a compressor board from the trimpot labeled 'compr'. When I lifted the metal can and saw the clairex photocells and el panel it felt like Christmas

 

[orangechili]

What else is funny is they used the A24  for the interstage here. I wish there was a schematic somewhere floating around on this... I would like to get it fully working before cannibalizing it for the mojo parts. I have tested most of the parts , opamps work well and sound killer. El panel lights well and T4 gets 120 volts ac with peak reduction cranked. I don't have the proper input transformer yet so held up a bit on that. I may just try to hand draw a schematic one of these days as i am slow with eagle still.

 

[shabtek]

trace the circuit, should not be too hard

 

[emrr]

I would probably use it as is if it's easy enough to do.  There are already enough LA-2A's made out of killed other things.

 

[orangechili]

All good points! I started hand drawing a schematic. I'm going away for the weekend but will hopefully have one done by early next week. The pinout of the T4 unit is different and doesn't use an octal socket(5 pins in straight line on bottom of the board) but I'll try to have both options of pinouts listed on it.

 

[orangechili]

I see the seller sold another board with melcor opamps on it, ones that run on +25/-25v. I've attached a picture of that board, i'm wondering if it belongs with my board somehow? The part number is one higher on this board which is 791807, mine is 791806.

 

[orangechili]

This board was set as a limiter by having the 2.7k resistor not on a switch i noticed. Interesting where the .0047uf 400v cap is located, I believe that's normally attached to the el panel.