[Collins] 6DF5 pin #7 not used in 75S3B?

[Dr. Gerald N. Johnson, electrical engineer]

Blow by comes from multiple sources. It comes from stray coupling
through the wiring. It comes from stray coupling between the filter
sockets and the filter switch wafers. It comes from the filter being
imperfect and having only a finite attenuation value in the near stop
band. That's a characteristic of the Tchebyshev pass band response curve
used to design the Collins mechanical filter. The Tchebyshev response
curve trades stop band attenuation for steep close in pass band skirts
with a characteristic notch between them. I don't recall the blow by
changing in my 75S3B when I added my mumetal shield. My shield isn't
grounded and I suppose by capacitive coupling to the hot input and
output circuits it could increase blow by detectably. Since the input
and output coupling is magnetic, I was concerned that with the plastic
case that adding the solid magnetic material might change the response
curve. I don't recall that it was detectable. Though that may be why the
factory shield is spaced from the filters while mine is snug on the
individual filter. My filter shield still fits when I have the tall
crystal filter along side. The factory shield won't accept the crystal
filter.

73, Jerry, K0CQ, Technical Advisor to the CRA.
-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.