Steven Swift wrote:

I am restoring a 1937 BC-312.

Nice radio.

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.

Unless you want authentic, I'd leave it as it is. The collins filter
is probably a lot more civilized in operation than a phased crystal
filter. Although, by playing with a phasing adjustment, you can vary
the width of the crystal filter from wide to narrow (with a bit of
ringing) for CW.

It depends on what you want to do with the set.
If you plan on copying mores code (CW) with it, you're probably
better off with the originla crystal pahsing circuit.

Jeff


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