The filter in that unit was a
Gilette double-edged type.

I remember one that could slice a QSO right in half,
with just a knock of the leg against the table.
Once kicked, I'd usually never find them again.
Not the most mechanically stable thing I ever saw, but
that was in jr.hi, and we used what we had...
Luckily, it was not my radio. :/ My first novice rcvr was
a hammarlund HQ-110...Not quite as kickable.
He later got a SX-40? that was half decent...You couldn't
kick a guy off freq with it.. :/ I've got an old national here
that looks about like a S-38...Someone gave it to me
years ago, and to this day, I've never tried to use it, or
plug it in... :/ I think it's cuz it reminds me of that S-38...
MK