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Author Topic: 813 amp project  (Read 21328 times)
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w8khk
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This ham got his ticket the old fashioned way.


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« Reply #50 on: January 17, 2021, 10:46:25 PM »

Thanks.  I will be doing some more testing tonight.  The coil was tapped with the help of a grid dip. Hopefully, I was close.

Looking at the photograph of the band switch on post 41, the interconnecting wires look rather long, and of small gauge.  Short wires, with minimum possible inductance and resistance are desirable here.  It is preferable to keep most of the inductance of the tank local to the coil, and not the interconnecting wiring.

A suggestion to improve the efficiency and stability of the pi tank would be to rotate the entire switch assembly clockwise 90 degrees (looking at it from the back).  Doing this would allow you to shorten all the wires, especially the common wire to the loading capacitor.  Perhaps also use a larger gauge wire, or copper strap, to reduce losses.  The wires need not be insulated, as long as they do not touch each other.  This improvement has the most benefit on the higher frequency bands, where the switch wiring is a significant portion of the total inductance.
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Rick / W8KHK  ex WB2HKX, WB4GNR
"Both politicians and diapers need to be changed often and for the same reason.”   Ronald Reagan

My smart?phone voicetext screws up homophones, but they are crystal clear from my 75 meter plate-modulated AM transmitter
w9jsw
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« Reply #51 on: January 18, 2021, 11:37:27 AM »

I happened to use the same switch on an antenna selector this weekend. I use the short lead approach. Turned it over to put the knob on and now it points south. So be aware. Will have to file a flat on the shaft to correct the problem. I love those switches, though.
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WQ9E
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« Reply #52 on: January 18, 2021, 02:22:03 PM »

I have used a bunch of those BC-375 tap switches and they are nice.  Hallicrafters used one for the band switch in their HT-45.

The spring on these switches is robust to put it mildly so the turning force is pretty high and a lighter force spring could be used while still providing positive selection.  For an amplifier project I needed to gang two of them with one mounted 90 degrees to the other.  I liberated a 90 degree gear drive from an old WRL Galaxy transceiver parts unit to couple the two switches and I removed the spring from the switch driven by the 90 degree offset gear set so that one switch provided the detent indexing for both.  Turning two ganged BC-375 switches with their stock springs intact would be a handful!

Rodger WQ9E
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Rodger WQ9E
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