[Collins] Mech. Filter loss in 75A-4

[Barockteer@aol.com]

Hi guys - 

I have a quaestion about the mechanical filters in the 75A-4, or rather a curious problem with mine:

I have a 75A-4, serial number 22xx, which came to me with a 6.0 and 3.1 Kc filters (back in those days, they were cycles, not hertz)! I bought a 500 cycle filter and added that in to.

I also did the factory mod to take the B+ off the filters.

The filters are installed as follows:

"A" - 6.0 Kc (Am)
"B" - 3.1 Kc (ssB)
"C" - 0.5 Kc (Cw)

In this arrangement, the loss through the CW filter is huge. An S-9 signal on the 3.1 kC filter drops to S-2 on the 0.5 kC setting, tuned for max.

If I swap the 3.1 and 0.5 filters in the radio, the CW filter is much closer to the ssb filter in gain, dropping only about 1 s-unit. In fact, all three filters are within an s-unit.

Does anyone know what to expect for insertion loss relative to bandwidth of these filters? I would expect the CW to be more lossy than the others, but not this much.

Also, does anyone know why the filter loss would be so much different for a particular filter in one socket than in another?

Thanks,

Tony, K1KP