[Collins] Wants:

[Dr. Gerald N. Johnson, electrical engineer]

Most mechanical and similar impedance crystal filters should work in the
A4. The problem will be in adapting while keeping the connections
shielded (though the latest mechanical filters sold through Inrad are
small). A long shielded wire from the opposite end will be harder to
tune because of the capacitance of the shielded wire, though there had
to be something like that INSIDE the A4 filter else the filter wouldn't
have worked. It should be that the tuning capacitors in the A4 have
different values. The filter end with the shielded wire should be
connected to the circuit end with the smaller tuning capacitor.

I think the 9 pin base of the filter (I'll know more in a few weeks
possibly) is exactly that of a 9 pin miniature tube. Used to be Vector
Electronics sold such plugs. Might be necessary to sacrifice a bad tube
and break the glass base away from the sides to get a plug. Another
technique that I've used is to start with a miniature tube socket, and
solder in 18 gauge (1 mm) solid copper wire into the socket pins. That
makes a plug, generally with a little flexibility and leaves the solder
tabs for the circuit. Neither tube sockets nor Vector plugs were in the
three catalogs I consulted this evening. But tube sockets ought to be
more available in surplus (like Mendelson Electronics) than plugs
because the plugs were never terribly commonly available.

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