Old QSL - Mode: RAC ?

[WB9UAI]

I collect old cards from my local area and just acquired one from 1933. The card reads:

UR _RAC_ sigs: QSA 4, R 6.

Transmitter: T.P.T.G. 750 volts, 210 tube.
Receiver: 224 + 227
Band: 7 MC

My question, what's "RAC"? The only thing that comes to mind is Raw A.C., like spark, but that's not right.

Ideas?

[WB9UAI]

Just occurred to me - T.P.T.G. = Tuned plate, tuned grid.

But RAC? Was spark legal in 1933?

[WB9UAI]

I found the answer to my own question!

http://forums.qrz.com/archive/index.php/t-67809.html

"Unlike the old "self-rectifying" raw a.c. rigs of the 1920's, this setup would use the triode tubes as a high power balanced modulator. Feed rf to the grids in parallel, but use a balanced pushpull plate tank circuit. The "carrier" would be balanced out, but there would be two "sidebands" 120 hZ apart: USB and LSB at 60 Hz. This would be basically a double sideband suppressed carrier transmitter tone modulated with 60 Hz a.c. There would be no raspiness or hash, just two carriers 120~ apart. The signal would be narrow and clean, and could be copied with a normal CW receiver or with a diode AM detector with no BFO."

Sounds cool !!

jw