Sunday, July 13, 2008

Ceramic switch

It has been bugging me for some time. I keep looking at other options on the web and auction sites. Time to settle the matter once and for all. I have two nice ceramic switches. They came out of a Collins millitary linear amp running two 4CX250F tubes and the switches were controlled by a motor. The problem is that the switch position is controlled by a third waffer therefor has no manual position indexing.

Without positive feedback the switch is next to useless to me and I know that making something to do the job is pretty tricky. 18 positions. The switch layout takes up 9 positions. It is a funny switch. It is designed for capacitive arrays. C1 & C2 with a powered rollor inductor making up a plate tank circuit.

It is ideal for what I want to do. I have a C1 of 230pf duel section and C2 of 1300pf. For 160m C1 needs to be around 400pf so the two sections in parallel should work. Switching out the other section for 40m and above. C2 needs to be 2200pf or more reducing to 1500pf for 80m.

So mounting an indexing mechanism was the task at hand. A search of my junk collection located a likely candidate. An old two position switch with a ball bearing in a spring mount. I prized the spring mount from the end of the switch and found it was made of two pieces of spring steel. A quick rustle around in my nuts & bolts bin located another ball bearing.

I mounted these on a piece of aluminum added two standoffs and a cam made of phonelic circuit board with 18 drilled indents topped off with another piece of aluminum. It worked pretty well but maybe I will make another cam as the indents are a bit deep.

The standoff spacers will allow the whole thing to be mounted front and back and the only thing left to do is to find some way of adding start & stop tabs at the right positions in the switches travel.

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