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Author Topic: Transistor for K6XX amp relay speed-up?  (Read 1102 times)
K8AC
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« on: January 21, 2004, 12:41:24 PM »

I have the amp on the bench today and thought I'd install the K6XX circuit for speeding up the antenna relay.  I wonder what transistor other Ameritron amp owners have used in this circuit -the relay reportedly draws around 100ma.  
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K0BG
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« Reply #1 on: January 21, 2004, 02:22:14 PM »

I'm not familiar with the mod, but if I wanted a solid state device for a relay driver, I'd use a FET. They are very fast switching (not really needed in this case), and have nearly zero resistance when turned on. Even one in a TO5 case can handle an amp easily.

Alan, KØBG
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K8AC
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« Reply #2 on: January 21, 2004, 03:21:15 PM »

I had a few NPNs in the junk box and found that the specs on the 2N2222 say it can handle 800ma. OK.  Wasn't aware that it would be that high for a 2N2222.  Anyway, built and installed the circuit and it works just as advertised.  

There's at least one rig (Elecraft K2) that's sensitive to the amp's relay switching speed.  It brings up carrier very fast before the amp's relay has transferred, thus seeing a high SWR from the open circuit.  The mod results in a higher than normal DC voltage being applied to the relay coil momentarily, thus speeding up the relay activation.  
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