1930's RCA passive mixer

[emrr]

1932ish RCA Victor four channel passive microphone mixer with low and high frequency attenuation circuits. I say 1932ish because 'Victor' was removed from all name plates on all the 1933 gear I've seen. And the 1930-31 equipment lines used slightly different knobs. Surprising how flat this thing is, given audio is passing through two pieces of early 1930's iron. This is equal/better response than you get out of a single Altec octal can or a Cinemag CMOQ-2S. This thing works perfectly. Roughly 200 ohm inputs and 500 ohm output. The PB model designation suggests it is part of the RCA Photophone equipment line, probably used for film work.

Response plots. These plots done with 200 ohm source and 560 ohm load, all attenuators set for minimum attenuation (pic shows max atten on all). Increasing attenuation has slight effect on extreme top end high frequency loss, but not significant with an input and the master set at 12 o'clock position. If you wind down three inputs to max attenuation, one at min, and master at min, you get roughly a 3 dB droop at 22 kHz.

Largest ladder attenuators I've ever seen; astonishingly overbuilt. These things are roughly twice as large as the average Daven type. RCA seems to have wound their own precision resistors too, as I've only seen these resistors in 1930's RCA gear. Appear to be dual bobbin winds; to minimize stray capacitance?

 

[Mailliw]

That is awesome. :grin:

 

[syn]

...it is indeed...

 

[abby normal]

Doug where do you get this stuff? Man that looks cool. :thumb:

 

[cannikin]

very cool,

I like the little stick figure the best... don't change that gives it character.

 

[Bryson]

That's insanely cool!

Imagine the retail price of something made like that now days.

 

[emrr]

I'm torn on whether to restore the front panel paint job. It is in excellent condition everywhere else, and wouldn't be hard to do. Have to slip some powdered lead into any repaint, of course. :green: Won't look right otherwise.

I'm always looking for weirdo historically significant audio pieces, as I'm a perv. Almost anything professional built before 1955 or so couldn't be built at all now. This thing would probably be $6K to produce in a similar fashion now. And I'm sure that's what it cost in relative 1932 dollars. The individual RCA broadcast amps of the day cost $5-6K apiece, adjusted for inflation.

It of course weighs 25-30 lbs. The shielding on the transformers is solid copper plate. Many of the broadcast amps have 3/16" solid copper faceplates(!). The first RCA mic preamp (1932-33) has an input transformer that weighs 10 lbs, as it's in 1/2" solid copper shielding(!!!).

 

[pstamler]

Not only that, but instead of a mere 11, it goes up to 20.

Peace,
Paul

PS I say leave the front panel exactly as it is.

 

[MartyMart]

[quote author="pstamler"]Not only that, but instead of a mere 11, it goes up to 20.
[/quote]


"Thats 10 more" !!!

:green: