THE COLLINS 30FXC TRANSMITTER
The 30FXC was introduced in 1936 as the successor to the popular 30FXB phone/cw transmitter, was rated at 200 watts output on AM and CW, and covered 1500 to 30,000 kHz.
During this period
Collins was being sued by RCA, AT&T, Westinghouse, and others (known as the "Radio Trust") over Collins' use of certain circuits whom the Radio Trust owned the patents on (purchased from deForest). Also at issue was the basic
deForest triode oscillator circuit patent controlled by RCA. As a response, Collins partnered with Amperex to produce and brand its own tubes. The workaround on the critical oscillator patent was for Art Collins to secure the
patent rights from Dr. Robert Goddard (of liquid fuel rocket fame) who had obtained a patent on his unusual external grid vacuum tube in 1915. Collins developed its own oscillator circuit around this unique tube having its grid on
the outside of the glass envelope. Produced by Amperex and branded the C100A, this tube was actually somewhat quirky in its operation and likely required component value "tweaks" to ensure reliable operation. Today the Collins C100
series tubes are among the rarest collectable Collins tubes.
30FXC
Transmitter
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Courtesy of Gary - WA9MZU
The C100A and the C100D were the only production versions of this unusual tube with the B and C being prototypes. In the 30FXC the C100A
drove a single 46 frequency multiplier, or a second cascaded 46 multiplier, depending on desired operating frequency. An RK20 intermediate amplifier feed the power amplifier tube, a Collins C201. The speech amplifier was built on
the modulator chassis and was designed to accept the recently introduced crystal microphone (a D-104). The modulators were RK31s (830Bs were alternates) operated class B.
The 30FXC used a total of 7 flush mounted panel meters. Two RF ammeters at the top were recessed from the front panel to reduce shunt capacity across the transmission line for more efficient operation at 30 MHz. The remaining five meters spanned the width of the transmitter just below the RF chassis and provided convenient monitoring of all critical current or voltage values.
The unit was 55" high, 13" deep, 19" wide, and weighed 260 pounds. It was finished in a black winkle enamel paint on the exterior and smooth aluminum paint on the inside.
A special RF section, the 10X, was offered for improved performance on the higher frequencies of 27 MHz and above
Plug-in coils were used for each band. The final
tank assembly was a variation of 45A final tank coil assembly. Instead of the double-duty driver/inductive neutralization coil, a separate driver and neutralization coil were used. As with the 45A, the entire assembly was
mounted on an mycalex base.
