I think you are right that the mechanical filter will be nice, but if it is
an SSB unit, won't the audio be messed up. I suppose that I should just leave
this part as-is until I get the rest working. Then if it sounds good, don't
touch it.

I always fight with myself regarding "authentic" versus better working.

Thanks.


Jeffrey D Angus writes:

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


--
"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety." Benjamin Franklin
"A life lived in fear is a life half lived."
Tara Morice as Fran, from the movie "Strictly Ballroom"
http://www.grendel.com

--
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

Steven Swift wrote:
I think you are right that the mechanical filter will be nice, but if it is
an SSB unit, won't the audio be messed up. I suppose that I should just leave
this part as-is until I get the rest working. Then if it sounds good, don't
touch it.

I think Peter's probably right, it's a 7KHz filter, probably just right
for "communications grade" AM radio operation. Which is you're going to
use this to listen to short wave broadcasting is a bit narrow. But good
for adjacent interferance.

Sideband sounds a bit "off" with these older receivers, as they use a
BFO with a large local signal mixed with the IF signal. Not too linear,
and the voice quality suffers a bit as a result. More "modern" SSB
receivers use a product detector (linear mixer) to add the BFO to the
IF signal.

Heh, then again, that was also a popular "modification" in the 50s and
60s as well. "Adding a product detector" to your AM/CW receiver for SSB
operation.

I always fight with myself regarding "authentic" versus better working.

The "big thing" in the 50s and 60s was to modify all the old war surpls
equipment to "make it work better than new." Some of the mods were good,
but were done by butchers. Others, no matter how meticulously they were
done, offered little or no improvement to the orginal operation.

Jeff


--
"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety." Benjamin Franklin
"A life lived in fear is a life half lived."
Tara Morice as Fran, from the movie "Strictly Ballroom"
http://www.grendel.com