[Hallicrafters] HT-37 Bias

[Al Parker]

Hi folks,
    Well I finally ckd the schematics, and did a measurement in my HT-32.
There is a difference in ckts in the bias supply from the HT-32 to
the -37.
    In the HT-37, a relay contact changes the bottom end of the voltage
divider in the bias supply to put 47k across the 18k resistor during
transmit, thus lowering the bias voltage then.  Conversely stated, the
HT-37 the switches the bias voltage to a higher value when in standby,
thus reducing, maybe to cut-off,  plate current.
    The HT-32 mk I  and HT-32A skems do not have this feature.  I ckd my
HT-32, which gets used weekly, and the bias does rise about a volt when
not in transmit, but that's just a function of current draw I expect, it's
not enough to change the plate current very much.
    It wouldn't be hard to use a set of the relay contacts in the -32's to
provide the -37's feature, maybe that's what W9YKA's  "Tube Saver" ckt
does.  David, next time you are into your HT-32B under the chassis, maybe
you could let us know what you find.
    Bill, K2WH, and Bill, AB0ZZ, how about measuring your HT-37 bias
voltage in both situations, MOX and standby?
    "inquiring minds need to know"  ;-)
73 all,
Al, W8UT