TECHNICAL SUPPLEMENT FOR THE SR-160 & SR-500 by WDØGOF August 2010
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SR-500 OVERVIEW
The Hallicrafters SR-500 Tornado is a ham radio transceiver designed for 500 watts input PEP on SSB and 300
watts input for CW on 20, 40 and 80 meters. Introduced in 1965 at a price of $395 plus $119.95 for the AC power
supply. It is in fact a beefed-up SR-160 using a matched pair of 8236 power output tubes in place of the 12DQ6B
pair in the SR-160. The 8236 is a heavy-duty carbon-plate tube and is not that common. The PS-500AC power
supply (on the right) is specifically designed for the greater power requirements of the SR-500. A matching mobile
supply, PS-500DC, was available at $149.95. The 12AU6 tube and the 100 KHz crystal for the crystal calibrator
were extra-cost options (installed in this set).
In comparing the schematics for the SR-500 and the SR-160, only a few differences are noted. R92 is 220K ohm in
the SR-500 and 180K in the SR-160. R96 is 56K in the SR-160 but removed from the SR-500. These resistors are
in the grid bias line, shown as -55 volts on the SR-160 schematic and -85 for the SR-500. The external bias power
supply input requirement for both sets is -100 volts. The 12DQ6B pair operates at 575 volts on the plate and the
8236 pair is supplied with 800 volts from its external power supply (750 under load). The 8236 requires more
filament current (and more plate current!). Nearly all other requirements and specifications appear to be similar in
the two sets. There is a zener diode switched in to stabilize the voltage on the VFO tube when in DC or mobile
service.
