Can I check ceramic capacitors with a hi-pot tester? I thought it would puncture and ruin them.
I have a 20KV 5mA supply and several super high value, 40KV rated resistors from TV set high voltage probes. I should be able to make a tester. Might be faster to buy one, but I have time. And some HV wire for the test leads.
hmm. about those fuses.. in any case it's a serious fail if a cap in the coupling position shorts.
Pat,
If the cap can take 10 KV hi-pot without failure (maybe 15 minute soak), and a few amps RF current without getting hot, then it should work. Hi-pot testing a cap like that till it leaks makes a failed part. If you have several of them, maybe sacrifice one and see where it punches through. Then that failed part makes its final rebuttal as it hits the trash can bottom and makes that familiar audible 'thunk'.
Since you have time, consider an RF current test. Several options exist. One almost insane idea is to use a bucket of salt water to make a ~ 500 ohm resistor. Then put an RF ammeter in series with the cap, and put the cap across the salt water resistor. Use your antenna tuner to match to the load, bringing up the RF power until the cap as the desired RF current through it. Vary the power, the resistance, and the tuner to let that cap take current. See if it gets hot. This arrangement would be similar to an auto-match used with commercial plasma etch machines. Those run at 13.56 Mhz.
If it takes the current, and can take a non destructive 10 KV Hi-pot, then it should be good for the Colonel Tucker plate B+ bypass cap. You still need a hefty RF choke across the antenna port to contain the DC surge if that cap were to short out. One of those tiny 2.5 mh pi RF chokes would blow immediately. I'd make something with 20 awg or larger cross section wire.
I once was tasked to use a 2 amp pico fuse on a circuit board to fuse a 360vdc buss that had lots of energy storage across it. These fuses are about the size of a 1/4 watt resistor. I had to test this with about 2200 mfd charged to 360 vdc, and with a knife switch dump the caps into the pico fuse. The fuse would blow apart instantly. Had to vary the PCB layout such that the fuse was mounted upright at about a 30 degree angle with one short lead, and one longer lead to the PCB about 1/2" away. The idea was to position the wires such that when it blows, the long wire had to fly back the other way, and not allow the current flow to restart again. In the case of this output RF choke on the Colonel Tucker, consider a knife switch test from your power supply at 3KV to see if the antenna shunting choke can handle the surge.
Now I feel like blowing something up...
Jim
Wd5JKO
