What set-up precautions are necessary to run through a coil-tapping process?
Here is what I've done so far...
With my tune and load capacitors mounted in their final positions in the RF
compartment, but isolated from the rest of the circuit (no tube, plate choke,
coil, output connections), I worked up a chart with turn counter values versus
capacitance values. I discovered in this step that my load cap would not
register a capacitance when the 2.5mH output safety choke was connected.
Should that be the case?
In the next step, I reconnected the entire circuit (tubes in place, plate choke
connected, plate load resistor connected from top of plate choke to chassis,
coil output safety choke). I attached an MFJ259B to the output with no coax
(using a male-male PL259) and went to work on coil tapping.
I used the PI-EL program to derive the intial capacitor settings. I was easily
able to find tap points for 50+j0 matches by tweaking the capacitors.
This is 20-40-80-160 amp, so here is what I ended up with (L and Q are
back-calculated)
20m calc Ctune=55 Cload=288 L=2.57 Q=12
20m real Ctune=39 Cload=436 L=4.0 Q=9.5
40m calc Ctune=109 Cload=573 L=5.1 Q=12
40m real Ctune=111 Cload=880 L=5.0 Q=12
80m calc Ctune=209 Cload=1100 L=9.79 Q=12
80m real Ctune=210 Cload=1360 L=9.87 Q=12
160m calc Ctune=431 Cload=2261 L=20.1 Q=12
160m real Ctune=343 Cload=1850 L=25 Q=9.54
So, what have I got? 40 and 80 look good, except for the higher than expected
Cload values. It looks like I need to rework the 20m tap. On 160, it appears
I got too much coil.
Am I on the right track here?
Steve KK7UV
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|