[R-390] Busted mechanical filters

[Charles A & Leonor L Taylor]

Jim M.beat and pounded on his keyboard:

"But how do you reassemble it?  What do you use for replacement foam, etc.
 Jim M."

Jim,

If I knew the answers to those questions, I wouldn't be asking for 
busted mechanical
filters. Hi.

Actually, the foam isn't that important as long as the filter is 
reassembled in conditions of
low humidity.

Then there is the problem of pulling a vacuum in the filter. Any gas 
will act to dampen
the vibration of the metallic disks, and thereby increase the 
attenuation. I suppose this
can be compensated by reducing the resistance the loading resistors on 
the other filters
and compensating by increasing the I-F subassembly gain by adjusting 
R-519 (GAIN
ADJ).

I repaired a plastic-encased Collins mechanical filter in 1973. I had to 
carefully saw
the plastic case circumferentially, and resolder the open transducer 
lead (#32 AWG,
perhaps). I observed no material change in attenuation (about 6 dB) of 
the filter
after gluing the case back together.

Incidentally, I believe that I mentioned I set R-519 (GAIN ADJ) by 
setting LINE
LEVEL meter to "100," with LINE METER switch set to "0," and LINE GAIN
pot set fully clockwise (that's with the top part of the knob going to 
the right, for
you kids who have never seen an analog clock). That's very close to the 
prescribed
setting, and is a convenient way to observe deterioration of the tubes.

I hope that's a good answer.

Charlie