I am restoring a 1937 BC-312.

A previous owner had installed a Collins mechanical filter in the 1st
detector stage (normally a coil with crystal phasing).

The Collins filter is part number 526-9395-00 and labelled "F 455 Z 7"

From google searches, it appears that this might be an SSB filter, but I
haven't found an exact reference.

Anyone know what this really is? I have to decide whether to "un-modify"
this stage or leave it as-is.

TIA,

Steve.
--
Steven D. Swift, , http://www.novatech-instr.com
NOVATECH INSTRUMENTS, INC. P.O. Box 55997
206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA