R390A pto as 160m vfo

Fri Sep 26 14:49:19 EDT 1997

Microsoft Excel and 2 other individuals have all verified my math--the R390A
PTO coil tunes  5.3-10.6 uH (not incl end-of-range overtravel) to give
3455-2455 kc with 390 pF, so with 1063 pF total capacity, it will tune the
range 1499.4-2120.4 at a rate of 60 kc/turn (note these calculations
conveniently ignore the few pF tube internal capacity) with serious diddling
of the trimmer inside the pto and the endpoint adjustment one could get
exactly 60 kc/turn at a starting point of 1500 exactly).
With this thought in mind, with a set of 10:6 ratio gears interspersed in the
chain somewhere, it is even theoretically possible to use the 390's own
Geneva Device mechanical digital readout...although I leave such fabrication
to the builder's choice and desires...my own tastes would run more towards a
51J/75A-style disc on a jackshaft driven 6:10 by the pto shaft.  Much easier
to fabricate.

73 de ka9egw

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