[Milsurplus] RCA Radios

[Mike Morrow]

Jack wrote:

>The AVT-112 has a little tag on the front panel that can be changed
>to show the primary voltage.
>
>The AVR-20 receiver also would need its filament string rewired...

The nice thing about the AVT-112 is that you "re-wire" the filament string via terminal strip jumpers.  The manual provides jumper info for:

1.  6v, using 6SL7GT for V5
2.  12v, using 6SL7GT for V5
3.  12v, using 12SL7GT for V5
4.  24v, using 12SL7GT for V5

The AVR-20, on the other hand, requires physical re-wiring, plus the addition of a 42 ohm resistor across the 6S7 filament for 12v or 24v ops.

I don't know why, but I've always really liked the RCA AVT-112 and AVR-20 combo.  It seems to me to be an excellent design in a small package.  The receiver manages to implement a super-het with RF stage, BFO, and AVC using only four vacuum tubes.  I bought my first AVR-20 for $1 as a kid in the early 1960s, then loaned it a decade later to my German instructor in college.  He managed to lose it in a house fire.  The transmitter is a very respectable crystal-controlled MOPA design with plate-modulated PA, plus an electric-eye tube tuning indicator.  If only that plastic antenna coupling control wasn't so prone to breakage, or so damned hard to fix!

I don't think so much of the three-tube AVR-15 beacon band receiver.  It's the same size as the AVR-20, yet it has no RF stage or BFO.  Likewise the AVT-15, which has only two tubes, both 6L6.  One is the modulator, the other is the modulated crystal-controlled oscillator.  Is it even legal to run such an animal on the ham bands today?  There's a fellow on the MRCA list who says he's going to put his "RVT-15" (??) on the air.

The Signal Corps bought both AVR-20/AVT-15 combos and AVR-20/AVT-112/AVA-126 combos.  All of the former that I've ever seen were set for 6v operation.  Most of the later that I've ever seen were set for 12v operation.  Like Jack, I've never seen one marked for 24v operation.

There's an interesting Setchell-Carlson beacon-band receiver of the same era called the Model 512.  Under military nomenclature it was called the R-76/ARR-13.  It was intended for 12v operation, so unlike the 28v-only BC-1206-C look-alike, it required a HV B+ supply.  The manual for the AN/ARR-13 specifies the use of the AVA-126.  That has me wondering if a complete typical light-observation aircraft radio suite might actually have often included the AVR-20/AVT-112/AVA-126 *and* the R-76/ARR-13, to provide the vital beacon band coverage that the AVR-20 lacks.  I believe the AN/ARR-13 is technically superior to the AVR-15, for it has an RF stage, and is smaller and lighter and easier to mount.

I've got a mid-1940 radio magazine ad somewhere that announced the AVR-15/AVT-15 combo.  The AVR-15 alone was $100, or about $1200 in 2007 dollars.  Evidently for the next couple of years this combo was a real hit with private light aircraft owners who had money to spend.

Mike / KK5F