Michael D. Harmon
mharmon at att.net
Thu Oct 23 23:19:46 EDT 2014
Hi Bob (and all),
The ART-13 is built like a tank, and everything about it is
under-speced. The dynamotor supply originally supplied with the radio
set only delivered 1150 volts B++ to the PA. The 813 is rated to 2000V
CCS and 2250V ICAS in Class C amp service (CW/FM). With 2KV at 180 mA
on the plate, the RCA TT-5 says it's good for 275W power output. Most
guys who build homebrew AC supplies try to keep the B++ down to
1200-1500V to extend life of the tubes. The 811 modulators are
behemoths. A pair of them in ICAS Class B service with 1500V on the
plates will deliver an unbelievable 340W of audio!
The biggest problem with the ART-13 as a general purpose amateur
transmitter is threefold: First it's only designed to operate between
2.0 and 18.1 MHz (although there are a number of guys who use it on 160M
AM). Second, there's no 'VFO' per se. The calibration book shows dial
settings for every kHz within its range, but there's no direct
correlation between the 'A' (Coarse) and 'B' (Fine) frequency controls
and the frequency being transmitted. Therefore, every frequency change
has to be spotted against a receiver on a known frequency. The
transmitter does have 10 'preset' (i.e. memory) channels for nets and
skeds. Once a frequency is programmed, a simple channel selection is
all that's necessary to set up the transmitter for operation on that
frequency (if you don't mind the whirring and clacking while the
mechanical marvel is doing its thing). Third, the ART-13 is designed to
load an end-fed airborne wire antenna. If you build some sort of
matching device, you could probably load up a coax-fed or balanced
antenna, but it wasn't designed for that application.
Whatever you do, PLEASE don't disembowel a perfectly good ART-13 with
the intent of 'modernizing' it! The mil surplus guys will hunt you down
and pin your coax!
For these reasons, I wouldn't put it in the same class as AM/CW
transmitters of the Fifties and Sixties. It really belongs in a vintage
Forties 'B-29' station, along with a BC-348 and a rack full of ARC-5 gear.
My two cents worth ...
Mike Harmon, WB0LDJ
mharmon at att dot net
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