[R-390] R390a Mechanical Filters

[Jim Whartenby]

Mark
The mechanical filers from the R-390A are the easiest to open and are the only filters I have been able to successfully repair.  If your filter is still working but a bit deaf then the problem is the "rubber" isolator used to hold the guts inside the tube has turned into goo.  If one of the coils measure open, then it depends on where the break is.  If it is at the feedthrough then a repair is possible.  If the break is in the coil body then the filter is toast.

Filters for the R-390A show up on eBay every so often but there is no guarantee that the filter's isolator is not in the process of turning into goo or that it will survive delivery.  Perhaps others on the list can comment on sources of the filters?

Does this reflector support photos?  I can send a photo or two of a filter that was not repairable and the isolator I made from some neoprene sheet that seemed to work OK in the filters I repaired many years ago.
Regards,
Jim

Logic: Method used to arrive at the wrong conclusion, with confidence.  Murphy

-----Original Message-----
From: mvjohn <mvjohn at sympatico.ca>
To: r-390 at mailman.qth.net <r-390 at mailman.qth.net>
Sent: Mon, Feb 27, 2023 1:00 am
Subject: [R-390] R390a Mechanical Filters

Has anyone found a suitable replacement for failing mechanical filters? My 4khz filter is shot - deaf - and repairing it does not look likely.

Mark VE3LU Sent from my Galaxy