[R-390] 4Kc filter replacement

[D. ball]

After weighing all the possable ways to solve this problem of finding a 
replacement filter I think the easest way is to try to find a exact 
replacement. Ok that sounds pretty simple except fot he fact that finding 
the ones in cylinder cases styles is a bit harder. After searching e-place 
for a while I find various collins filters that have the same center freq. 
and the same rated bandwidth. They even have the same part number minus the 
case style. So the idea here is to locate a collins filter, which does not 
seem to be a problem, remove the filter element from the existing case and 
install it into the cylinder case I have left from the 390a. I assume that i 
would dissamble most any drum head type collins filter rated at the same 
spec and find the element inside to be the same or real darn close. The 
advantage is I can find any case style a lot easer than just one style case. 
Second is it really should be the same element inside and thus becoming a 
drop in replacement without matching concerns or really drifting away from 
the original design. By the way the input i have gotten from other members 
on the mailing list on this topic have been great. I would like to give a 
thankyou to all those who have thrown in their input and ideas.
Joe
KE1MB

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