[Collins] need cw filter 75S-3

[Dr. Gerald N. Johnson]

The orignal S-1 CW filter was a Y type case, about 7/8" diameter and 
3-1/2" long held by a clamp and with the connections soldered to the 
terminals on the ends of the filter. The 3B/C introduced the plastic 
cased FA filter that plugs in. The sockets were exactly those for a TO-5 
transistor, three pins on 0.2" centers like the catalog number 575-93103 
from Mouser Electronics. The Inrad filter doesn't appear to be made for 
soldering to the terminals but those sockets could be used. The clamp 
space would need to filled with some packing material. The FA filter 
included threaded studs that Inrad neglects to provide that could have 
been used to mount the filter.

Early KWM-2 used the Y cased filter and the late KWM-2 used the FA 
filter and simply soldered wires to its pins and changed the mounting 
bracket

The S-1/2 CW option used a 526-9367-00 500 Hz CW filter and associated 
crystal, 290-8707-00 455.8 kHz.

My book shows the S3/3A used a Midland 300 Hz filter, 293-0843-00, 
Midland M3-0843. That shows up as a rectangular can probably nearly an 
inch square by 3" long with solder terminals on the ends. My schematic 
shows the CW filter terminations included 7-60 and 33 pf capacitors in 
parallel while the SSB filter used 7-60 and 100 or 82 pf capacitors so 
the Inrad may need more tuning capacitance to resonate the ends to match 
the tuning of the 3B/C. It should be practical to use the transistor 
sockets from Mouser or one's parts bin to mount the Inrad plug in filter 
with the added tuning C and perhaps added wire lengths. It used the USB 
BFO crystal or the tunable BFO for CW.

I think that way the Inrad filters for the 3B/C will fit the 3/3A. Might 
want to make a mounting bracket for the sockets.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association

On 5/31/2011 10:53 AM, yash at aol.com wrote:
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>   Iam in need a a cw filter for my 75-S3  ,I beleive its 300cps ,but 200 to 500 cps would also work,I think. I contacted Inrad, they have filters for the 75S-3  B/C with mounting board to snap in. I asked if the filter could be removed from the board and installed into a 75S-3, they said ,didn't think so. If anyone has the proper cw filter ,please get back.  or has another solution for the problem.
> thanks
> 73 dale wt4t
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