[R-390] 390-390A PTOs

[Jacques Fortin]

Hi Russ,

Long time !
Hope you are well.

There is two variants of the Collins 70H-2 PTOs for the R-390, the original
one and the "MOD 1".
This MOD 1 variant is close to the Collins 70H-12 used in the R-390A, but
not in every aspect.
See attached p. 12 and 14 of the TM11-5820-357-35.
Apart of the output connector that is a full-size BNC in the 70H-2 compared
to the "mini" one of the R-390A version, the screen grid bias resistor for
the 5749 have a different value(s) and the power connector pinout is
different.
Despite this, I believe that a 70H-12 (or any other brand of R-390A PTO) can
be "adapted" to a R-390, providing that the mechanical mounting parts of the
R-390 are used.
The other way round, the a R-390A PTO is NOT a straight drop-in solution for
the R-390.

73, Jacques, VE2JFE
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