" Uncle Peter" wrote in message
news:CFL0d.188965$Lj.138912@fed1read03...

"Steven Swift" wrote in message
...
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"



I'm going to guess 7-kHz bandwidth.

Pete

I think you may be right; or close!
Just did a very quick search and one hit www.wa3key.com/filters.html
shows a filter labelled F455FA-21 describing this as 455 kHz centre
frequency and bandwidth as 6 db. down at 2.1 (that's two decimal one)
kilohertz. It also mentions "All (filters) have the steep sided skirt
selectivity common to all Collins mechanical filters".
BTW a little further on it says something about the use of filters with
different bandwidths; maybe the OP has a 700 Hz (O.7 kHz) or so called 600
hertz CW operators IF filter? Or maybe a so called 6 kilohertz AM filter.
And it would be, placed instead of the crystal filter, in the front end of
the IF immediately following the first mixer.frequency changer?
The rec.radio.amateur.boat anchors news group might be good place to
ask; also I think I've seen a description of Collins mech. filter
nomenclature some years back, on the internet somewhere!
Cheers.