Experimenting w/ shorting unused section of roller inductor before I replace it with some other device.
1st try yesterday:
5.6uH molded choke (1w sized-body) series connected to a 250w 50 ohm RF termination resistor w/ heatsink (TO-220 size). Seemed ok on 10 & 11 and 20 into DL with 5w AM drive, using only 1 plate xfrmr (1800vac, 400mA, FWB). Saw 600-ish watts for few moments on each band 10, 11 and 20 before I tried 40. Heatsink on 250w RF R not even warm. I was feeling optimistic, yeah?
40m always shows higher PO and saw the expected 750-ish but after a 4-5 seconds the molded choke flashed brightly. A bad smell & bit of smoke but choke body still intact. Disassembled picture shows darkened choke. It was a brighter green before experiment. A small bubble on 1 side from heat but still show conductivity on VOM.
2nd try today:
This time I did not bother with 10,11 & 20. Amp was still set from yesterday. I replaced the molded choke with a homemade choke: A 5w 200R mox with 1 layer of 24awg magnet wire the full length. Not much room in front of Roller by the open/unused terminals so to prevent arcing, I wrapped homemade choke in 1 layer of HV glass tape plus 1 layer Kapton. Resistor got hot very fast (5-10 secs) but saw the same 750-800w PO (although this time it was CW not AM). This time the Term R got hot too. Heatsink too hot to touch, fast. Picture shows the wrapped wire discolored from heat.
Next try
I admit that I expected PO to go way down with the unused ends of coil shorted. Maybe a simple wire closing the ends is not the defeat I expected it to be. There will be more on this. The rest of the amp running fine after the rebuild last few months. The Input working great (red LEDs to show what band its set for, hooray!) The Blower motor noticeably smoother with the series connected 70uH power inductor after the triac speed control.
n2eye
Edit: In fact next try will be down to 50R the RF Term is 250w so I'll try larger heatsink.
1st try yesterday:
5.6uH molded choke (1w sized-body) series connected to a 250w 50 ohm RF termination resistor w/ heatsink (TO-220 size). Seemed ok on 10 & 11 and 20 into DL with 5w AM drive, using only 1 plate xfrmr (1800vac, 400mA, FWB). Saw 600-ish watts for few moments on each band 10, 11 and 20 before I tried 40. Heatsink on 250w RF R not even warm. I was feeling optimistic, yeah?
40m always shows higher PO and saw the expected 750-ish but after a 4-5 seconds the molded choke flashed brightly. A bad smell & bit of smoke but choke body still intact. Disassembled picture shows darkened choke. It was a brighter green before experiment. A small bubble on 1 side from heat but still show conductivity on VOM.
2nd try today:
This time I did not bother with 10,11 & 20. Amp was still set from yesterday. I replaced the molded choke with a homemade choke: A 5w 200R mox with 1 layer of 24awg magnet wire the full length. Not much room in front of Roller by the open/unused terminals so to prevent arcing, I wrapped homemade choke in 1 layer of HV glass tape plus 1 layer Kapton. Resistor got hot very fast (5-10 secs) but saw the same 750-800w PO (although this time it was CW not AM). This time the Term R got hot too. Heatsink too hot to touch, fast. Picture shows the wrapped wire discolored from heat.
Next try
I admit that I expected PO to go way down with the unused ends of coil shorted. Maybe a simple wire closing the ends is not the defeat I expected it to be. There will be more on this. The rest of the amp running fine after the rebuild last few months. The Input working great (red LEDs to show what band its set for, hooray!) The Blower motor noticeably smoother with the series connected 70uH power inductor after the triac speed control.
n2eye
Edit: In fact next try will be down to 50R the RF Term is 250w so I'll try larger heatsink.
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