[R-390] VFO End points

[k2cby]

The standard Collins VFO contains three fixed capacitors in parallel with
the coil: C701 (370 pF), C702 (10 pF) and C703 (10 pF). Two of these are
tiny bits of naked mica with deposited silver on either side connected into
the circuit by very thin wire leads.

 

Particularly if the VFO had gotten damp, these tend to deteriorate. When
they change value they alter the spread between f(max) and f(min) of the
VFO.

 

Before even thinking of diddling the linearity stack, try replacing these
with NP0 ceramics.

 

So far as I am concerned, the linearity stack adjustment is strictly off
limits. Strong men have been reduced to quavering wrecks trying to adjust it
without the slotted shield cover that Collins used. (Why do you think Cosmos
came along?)

 

 

Miles B. Anderson, K2CBY
16 Round Pond Lane
Sag Harbor, NY 11963
Tel.: (631) 725-4400

Fax.: (631) 725-2223
e-mail: k2cby at optonline.net