My information says that the IF frequency is 470 Khz. Perhaps the IF
frequency has been changed to 455 Khz on the receiver in question to
suit the added filter.
Lionel L Sharp, VK4NS

nhoj wrote:
Steve---- What is the IF frequency of the BC 312. You are using a 455
khz filter. John

Steven Swift wrote:

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.