Re: {Collins} Mechanical Filter Internal



Hi Bob,

I used what I had: some dark gray fine-celled fairly firm shipping foam. I touched my soldering iron to it, and yes it melted, so I tried putting the foam on some single ply cardboard on a metal plate, heating the metal plate, and the cardboard kept the foam undamaged. So I made a tube of the cardboard to just fit in the filter tube, put the cut foam and the transducer into the cardboard tube and slid the whole thing into the filter tube. I cut the foam so that it compresses a bit in the tube and grips the ends of the transducer fairly firmly. After the filter was soldered up, it worked fine, and I could feel no movement with gentle shaking. I did them all the same way, and they all have worked fine. Will it last 50 years? Don't know, but it certainly beats throwing non-working filters in the trash!

Fred VE1FA

PS By the way, I found that a standard 120W Weller gun generated enough heat to pop the end off an R-390A filter pretty easily. But, be careful not to pull hard when the solder is softening, or you risk suddenly jerking the cap free, and snapping off both tiny wires inside!


At 06:40 PM 27/01/2012, you wrote:
What kind of foam should be used? I have a filter I'm considering restoring, and I'm worried about the foam melting when I solder the ends.

73
Bob VE3TOU

On 1/27/2012 4:11 PM, Fred & Helen Archibald wrote:
Hi Buck,
I've successfully fixed/rescued 5 R-390A filters. In all of them at least one of the extremely fine wires connecting the transducer coils to the filter terminals was broken. They broke because the foam which had originally supported the transducer/resonator assembly in the filter housing had rotted and the weight of the assembly was supported only by the fine wires. I put new foam in, resoldered the wires (takes a fine tip and a steady hand and a magnifier), then resoldered the ends back on. Did you have continuity between the 2 input terminals? Between the 2 output terminals? If not I expect this was you problem. If you did have continuity, I'm not sure what your filter problem is, perhaps a broken resonator support wire.

Best of luck,

Fred VE1FA



At 10:14 PM 26/01/2012, you wrote:
Have a 75A-4 filter that was not working. Thought I'd open it and see if there was any chance of bringing it back to life. Actually got the cover off without damaging--I think--the internal workings. Found some broken wires at both ends of the filter (top/bottom). Not quite sure which wires go where.


I have looked unsuccessfully for a sketch of the inside of an A-4 filter. Was almost certain I saw one somewhere but cannot find it.


Can someone direct me to a filter sketch/schematic?


Thanks.


Buck W0LC
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NETS: Tues & Thur: 3.805 MHz-2000 Central + Fri: 3.895 MHz-2000 Pacific
 SUNDAYS: 14.263 MHz-2000 UTC  +  AM Net: 29.050 MHz-1200 Central
 1st Wednesday AM Net 3.880 MHz-2000 local (ET, CT, MT, PT)

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