[R-390] 70H2 vs 70H12 Permeability Tuned Oscillators

[Larry Haney]

Hi Jim, I believe yes and no.  This is based on a post that Jacques Fortin
made a while ago about them having different screen dropping resistors (75k
for the 390 vfo and 56k for the 390A vfo).  This is due to the difference
in B+  feeding them (180 in the 390 and 150 in the 390A).  So, the one from
a 390 could be used in the 390A, but not the reverse, without changing that
resistor.  Putting a 390 vfo into a 390A would result in lower vfo output,
which is not necessarily an unlivable situation.  But, if I were doing it,
I'd change that resistor - better carrier level meter operation, s/n, and
overall gain.

The mounting  brackets would need to be changed, but from what I can
determine, the shaft diameters are the same, so that should not be an issue.

Regards, Larry

On Fri, Sep 13, 2024 at 1:41 PM Jim Whartenby via R-390 <
r-390 at mailman.qth.net> wrote:

> Other then the obvious difference in RF connector and power cable routing,
> are they interchangeable?
> Jim
> Logic: Method used to arrive at the wrong conclusion, with confidence.
> Murphy
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