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-   -   RCA SAGG-024 amp schematic needed! (https://www.gearslutz.com/board/geekslutz-forum/1293044-rca-sagg-024-amp-schematic-needed.html)

sameal 1st January 2020 05:01 PM

RCA SAGG-024 amp schematic needed!
 
2 Attachment(s)
I dunno why RCA schems are so tough to come by. But this ones no different. I can't find anything.

Right at the power cap cans somebody cut the diodes (cer71) which i replaced with 1n4007. There was also a little resistor i had to resolder, but i really need the schem to be sure everything went back right.

All the transistors test ok. The hfe ranges are all over though. 80-120ish. I need a replacement for AO232 which im also having trouble finding.

When i brought it up on the lightbulb limiter the first time, the diodes to the system were cut, so i got no short there. Putting the diodes and resistor back in i get a big bright bulb (short)

Any help would be great!

cathode 1st January 2020 06:18 PM

Quote:

Originally Posted by sameal (Post 14417626)
I dunno why RCA schems are so tough to come by. But this ones no different. I can't find anything.
!

RCA Service Company, in the latter days of their existence, sourced and re-branded products from various vendors, including Shure and McMartin.

Jay Rose 2nd January 2020 02:20 AM

That piece really doesn’t look like RCA-built broadcast, film, or speech (PA) gear.
One thing to check: just about every “native” RCA piece had an “MI-“ number on its nameplate.

sameal 3rd January 2020 11:01 PM

2 Attachment(s)
It very well could be a sub contracted job, but who?

It's labelled rca all over the place. But no clues as to some other manufacture doing it for them.

cathode 4th January 2020 12:24 AM

Rca sagg-024
 
Quote:

Originally Posted by sameal (Post 14423278)
It very well could be a sub contracted job, but who?

The rear panel labeling looks McMartin.

Jay Rose 4th January 2020 01:32 AM

Looked closer at your first photo. The 70.7v tap clearly shows this was a piece of public address equipment... AFAIK, that's the only application that uses "constant-voltage" distribution to multiple speakers. (Each speaker had a transformer with a 70.7 V primary, and a bunch of secondary taps marked in watts, so you could easily set how much power went to that room. No messing with impedance... just make sure your total secondary wattage didn't exceed the amp. There was also 25v constant voltage, which had the additional advantage of class II wiring.)

Then I went to an archive of RCA catalogs, and looked at the PA amps in an early 70s version. None of them looked like your box. RCA's front panels were very different.

RCA -did- have PA amps in the "SA" series (I think it stood for 'speech amplifier'). But never SAGG as far as I know. And as far as I could determine, all of them also had MI ordering/stock numbers somewhere on them.

sameal 4th January 2020 04:10 PM

Quote:

Originally Posted by Jay Rose (Post 14423618)
Looked closer at your first photo. The 70.7v tap clearly shows this was a piece of public address equipment... AFAIK, that's the only application that uses "constant-voltage" distribution to multiple speakers. (Each speaker had a transformer with a 70.7 V primary, and a bunch of secondary taps marked in watts, so you could easily set how much power went to that room. No messing with impedance... just make sure your total secondary wattage didn't exceed the amp. There was also 25v constant voltage, which had the additional advantage of class II wiring.)

Then I went to an archive of RCA catalogs, and looked at the PA amps in an early 70s version. None of them looked like your box. RCA's front panels were very different.

RCA -did- have PA amps in the "SA" series (I think it stood for 'speech amplifier'). But never SAGG as far as I know. And as far as I could determine, all of them also had MI ordering/stock numbers somewhere on them.

Interesting.

This does have an 8ohm tap, my thoughts were to use it more as a guitar type amp, if it sounded any good. Looks to be all germanium on the inputs, with plug in transformer options. I got a bunch of octal plug transformers and sockets i could mount transformers too.

Ill poke around more for the mi number.

Jay Rose 4th January 2020 04:32 PM

Another couple of clues:

1) The nameplate says "rack panel", not "amplifier" or "monitor". The stock number doesn't tell us anything, because while RCA sold blank panels for their racks, they never wasted space on them in their catalogs.

2) The RCA logo is an older-style one, from the tube era. By the 1970s, RCA was using three san-serif outline letters as their logo... with no circle or lightning bolt.

3) Gadgets on the right of the panel -- fuse, switch, light -- aren't mounted on the panel itself. They're mounted on the chassis and show through holes drilled in the thicker panel. I can't imaging any industrial designer, let alone one at RCA, doing something that way.

My hypothesis: a station engineer took a spare RCA panel and mounted a chassis-only amp, of some other brand, on it. The front panel labels could be decals or rub-on letters (common in that day), or maybe when they had a sheet-metal shop do the drilling, they had it silkscreened.

cathode 5th January 2020 06:51 AM

Rca sagg-024
 
1 Attachment(s)
the power supply resembles the McMartin LT-80b.
a few component differences but you get the idea.

note the half wave rectifier section for the accessory socket power.

maybe 3 amp or greater diodes rather than 1N4007.