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.
--
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 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

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

"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

" 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.

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.

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.

Yes, the previous owner added caps on the IF to tune it down to 455. The job
is well executed-- not hacked. I am just looking for the real specs on the
part. Perhaps this was modified by a CW or SSB guy.

Lionel Sharp writes:

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.




--
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 in message
...

Yes, the previous owner added caps on the IF to tune it down to 455. The
job
is well executed-- not hacked. I am just looking for the real specs on the
part. Perhaps this was modified by a CW or SSB guy.


Might have been modified by an AM guy, since the 7-kHz filter
passband would yield a 3.5 kHz AM bandwidth.
Odd that he padded the IF stages--I'd have
thought they would have easily tuned down another 15kHz without issue.

Pete