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Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Roger, yes it's the high power tube but the heater broke during shipping If I ever find a similar tube, I will never let anyone ship it to me but I'll transport it by myself instead.
I got another air cooled metal-to-glass tube which should be good for several kilowatts and I'm planning a vttc with it, but for now I'll finish this one.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
I think I found the source of the loud buzzing spark - look at this scope shot of plate supply voltage! (sorry for blurry pic)
2kV/div, 5ms/div
There is a voltage spike on the leading edge of the pulse. I thought it was the result of slow reverse recovery time of the microwave oven diodes used, but after replacing them with a string of BY133 diodes the spike is almost the same. I may try using some fast recovery diodes but don't know if it helps.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
The main source of the problem has been found - a rf bypass capacitor which had a too high value (~27 nF) was causing the voltage spike. After replacing it with a 3.75 nF one, the spike is much smaller, sparks sound smoother and most likely are less branchy.
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
Dr. Kilovolt,I also wonder if it has something to do with half wave rectification as well as a FO of 350 to 450 khz. I have also seen pictures of coils that are not tube based but have half wave rectification and exibit sword sparks. the QCW coil seems to owe part of its sucsess ti its ramped input.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
I know, the spark shape has to do with the rf envelope and frequency. I was just wondering why my sparks were more branchy, as I found it was due to distortion of the rf envelope. But still I don't know why does the rf bypass cap value affect the envelope that much.
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How to get straight "sword like" sparks from a tube coil?
If I ever find a similar tube, I will never let anyone ship it to me but I'll transport it by myself instead.
