THE COLLINS 30J TRANSMITTER
Perhaps the Crown Jewel of the
prewar Collins transmitters, the elegant 30J was the last amateur transmitter produced before Collins regeared for the war effort. The 30J was a general purpose transmitter "designed for general applications such as police
service, aeronautical ground stations, or general purpose point-to-point communications where service is intermittent." Announced in the The 30J was 40% more powerful than its predecessor, the
The first 30J series included Collins tubes, specifically the C100A oscillator, and a pair of C101 RF output tubes. The RF deck underwent a complete
redesign using the 7000 series plug in coils employed in the 32RA low-level RF stages. The driver stage, a pair of 807's, used a plug-in shielded box to house it's tank coils. The most radical redesign, however, was the output
tuning chassis. Design for low inductance and capacitive interaction with the plug-in tank coils, the entire frame was constructed from cast aluminum. It was mounted directly above the RF deck and provided easy access to plug-in
coils, which were wound on 2.5" by 6" coil forms.
30J
Transmitter
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Courtesy of Gary - WA9MZU
The standard output was balanced, but a phasing coil option could be added to convert the output to unbalanced.
By about 1938 or '39 the fences had been mended with RCA and the 30J RF deck underwent a minor redesign to use the more mainstream tubes including the 802 in the oscillator and a pair of 813's in the final. This model was designated the 30J-18.
The 30J-18 used an 802 crystal oscillator stage feeding either an 807 frequency multiplier, or a
pair of 807 buffers (selectable), which drove the push-pull 813s. The modulators were a pair of ZB120s, similar to 838s but zero-bias. Plug-in coils were used to set the desired frequency range, then tuned with trimmers or sliders
to resonance. Its of particular interest is that while the 30J followed the 30FXC, its styling is dramatically different. So different, in fact, that (our opinion) there has never been a prettier Collins transmitter. Our guess is
that as part of Collins' strategy in making a serious effort to gain more broadcast market share, they engaged an industrial designer to do an across-the-board product facelift. The 30J was in the right place at the right time. Its
distinct Deco influence can also be seen on the Collins broadcast audio mixers and transmitters from about 1936 to 1938. The unit measured 60" high, 20" wide, and 13" deep and weighed 386 pounds. It was finished in a St. James
gray crinkle and featured a hinged rear door, coil access window, and a meter panel mounting behind glass: all firsts for a Collins amateur transmitter.
