[Collins] CW filter help please

[Dr. Gerald N. Johnson]

On Sun, 2006-10-01 at 13:10 -0400, TJRachwal wrote:
> Hi Guys,
> 	I have a 75S-1 that I want to put a cw filter in.  I see Collins 
> says an F455Q-5 is the 500 HZ filter.  I can't seem to locate one of 
> those but there is an F455Q-1 available.  Does the -1mean 1 KC 
> wide?  Does anyone have any idea or do you have a source for the F455Q-5?
> Tnx Ted K8AQM
> 
> 
I don't know what the F455Q-1 is. I've been through the one on line
listing and I have my doubts, I've been through two on-line lists of
mechanical filters plus my file folder of four or five mechanical filter
catalogs and NOWHERE do I find an F455Q-1.

What I see is that the letter after the frequency designation shows the
case except for SSB filters that have a Z in that position and Q filters
that are not quite within the numbering scheme. Q filters have various
cases. A Y case filter (typical of the 75S-1 filters including the
F455Q-5) would be called F455Y-05 through F455Y-35 for bandwidths of 500
Hz to 35 KHz. E.g. 2 digits EVERY time. The -5 on the F455Q-5 doesn't
fit the scheme because the F455Q-7 is 3.1 KHz. So for Q and Z we can't
trust the last number to be bandwidth.

The one on-line listing with F455Q-1 claims 1 KHz bandwidth and a "tall
V" case which is rectangular, metal case with pins on the bottom like
the FA plastic case used in later S-line. It still could be soldered in.
I see on that page that the part number is listed as 526-9308-00. I'm
suspicious its really an F455Q-7 with part number 526-9380-00 which is a
3.1 KHz filter in a J case with pins on one end to fit a miniature tube
socket as used in the 75A4. The link to the passband curve doesn't work.
That page may be old.

Besides the F455Q-5 filter, the S-1 needs a CW BFO crystal at 455.8 KHz.
Else the audio passband would be shifted to something like 1100 to 1600
Hz. using the USB crystal. But without circuit modifications that won't
work because there won't be a crystal connected in the CW position. It
doesn't look like a simple jumper on the crystal select switch wafer
will allow using the USB crystal for CW.
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer