[R-390] 4KHZ filters

[Bernie Nicholson]

I think that it would be a very difficult job to repair filters a jig =
would have to be made also the parts internally are SPOT welded together =
. the smallest welds I have seen ever . to remove the ends off the =
filters I used a Jewlers gas torch you have to be quick and when the =
solder melts you remove the ends abt 1/8 inch so as not to break the =
fine wires, BUT to get the filter assy. out you have to  cut the wires =
to the end cap on one end then you can slide out the resonator assy. the =
filters transducers DC resistance is 48 ohms  , I think the cheapest way =
out would be to fit Murata ceramic filters which are available in =
various bandwiths at 455khz , on a different subject I have just =
linearized a PTO by making a little jig and using the dial from a ten =
turn pot to draw graphs untill I got a straight line response It took =
abt 5 hours and when I put the cover on I only had to make a slight =
ajustment to the end stop and it is within 300 hz from one end of the =
dial to the other , A win for me anyway regards to everyone Bernie =
Nicholson VK2ABN


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