Note
Released about the same time as the TX-1, and looking very much like a miniature version of it, the Seneca was Heath’s first serious piece of VHF gear.
The Seneca covers from 50-54 MHz and from 144-148.3 MHz and will operate AM or CW. The rig is built around 11 tubes including a pair of 6146 finals and has a rated power input on six-meters of 140 CW and 120 AM. On two-meters the input power rating is 110 watts CW and 95 watts AM.
Features include carrier controlled AM operation, and frequency control from the built-in VFO or one of four FT-243 crystals. Although Heath advertised that the rig included “two power supplies” only one transformer is used, and it supplies both high and low voltage. The VFO used is the same one used in the TX-1—a 6AU6 running as a Clapp oscillator (a series tuned Colpitts).
The VFO output is from 8.000 to 8.222 MHz on two-meters and 8.333 to 9.000 on six meters. On six-meters the crystal frequency times 6 equals the operating frequency, and on two-meters the multiplier is 18. Obviously, on two-meters any drift in the VFO is going to show up in a hurry. A QST reviewer noted that when using the Seneca for two-meter CW, “you’d better use a crystal if you want other CW men to think highly of you.”
The VFO dial drive mechanism and the band switch linkages are frightening but actually work quite well—though trying to repair them may lead to an as yet unnumbered Excedrin headache.
Neutralization of the 6146 finals is accomplished with a pair of wires running along the outside of each tube. During initial tune-up these wires are bent and moved to a position that yields the lowest reading on a grip dip meter. The scheme works well enough.
Front panel controls include frequency control, meter function, buffer tune, final tank coupling, multiplier (tunes multiplier plate circuit to 2 times input frequency for six meters, 3 times for two-meters), loading, drive tune, final tune, function (off, CW, standby, AM), band switch, main tuning, and “spot.”
The illuminated front panel meter reads multiplier grid current, driver grid current, final grid current, final plate current, and final plate voltage. Basic meter movement: 1 mA, 50Ω. Rear panel connections include a mic connector, S0-239 antenna connector, a standard quarter inch key jack, and a ground post. There is also a rear panel octal accessory socket (refer to Figure 1). This socket provides a remote means of keying the transmitter, a 120 VAC output for an antenna relay, and contacts for receiver muting (wired normally closed).
The Seneca is painted with the same two-tone green as the TX-1 and is housed in a one-piece copper-clad steel enclosure. The knobs are satin finish aluminum as opposed to the polished aluminum knobs used later on the HX-30.
In spite of the fact that Heath kept it on the market for almost five years, interest in the VHF-1 was never very high and comparatively few were sold. Heath never made a matching receiver.
CRYSTAL CALCULATIONS
Crystals are located on the chassis between the meter and the power transformer. Crystal type: FT-243.
2 Meters: Operating frequency = crystal frequency x 18
6 Meters: Operating frequency = crystal frequency x 6
Refer to frequency charts for HW-10 (6 meters) and HW-20 (2 meters), as these units use the same multiplier scheme
References:
Review. QST. Jan 1961, p. 48.
Review. CQ. Sep 1960, p. 41.
Review. Electric Radio. Sep 2012.
TVI precautions. CQ. Jul 1961, p. 76.
Improved modulation and keying. 73 Amateur Radio. Jun 1962, p. 56.
Drive trouble (brief). CQ. Mar 1965, p. 67.
Chirp fix (brief). CQ. Jul 1973, p. 14.
Use as a two-meter FM amplifier. Ham Radio. Mar 1989, p. 8.
Frequency coverage: 50-54 MHz and 144-148.3 MHz
Power output:
6 meters: 140 watts CW, 120 watts AM (peak)
2 meters: 110 watts CW, 95 watts AM (peak)
Output impedance: 50-75 Ω
Output coupling: link (coaxial)
Operation: Crystal (four sockets provided) or VFO, CW or AM
Audio: screen modulation, controlled carrier
Power requirements: 117 VAC, 60 Hz, 120 watts idle, 400 watts full output
Size: 16.5 wide x 10.25 high x 10 deep; Weight: 50 lbs
Tubes: (1) 0A2, (1) 2E26, (1) 5R4 (1) 5V4, (1) 6AU6, (1) 6AQ5, (1) 6AN8, (1) 6DE7, (2) 6146, (1) 12AX7
Photos, general information and specifications from "Heathkit: A Guide to the Amateur Radio Products," by Chuck Penson, WA7ZZE. Used with permission.
