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304TH Tube Coil and Level Shifted supply
All,
I have found that the level shifted approach to feeding the plate on a tube
coil, as first mentioned by Dave Sharpe, is indead a most efficient method.
Currently I am employing a single 304TH triode, as essentially a drop in to
my 833A tube coil and can get a 16 inch discharge at just over 1000 Watt
input power. My specs and results:
13 inch by 3 inch #28 magnet wire secondary = ~13mH
Primary is 6 inch diameter close wound with 21 turns PVC insulated #12
Grid coil has 22 turns on same form as primary of #22 PVC insulated wire,
close wound 1/2 inch above primary
Tank cap is 0.0016 uFd
Grid leak cap is 0.001 uFd
Terminal Capacitance is unmeasured, but probably ~around 3-5 pico farads
15 Inch Spark :
10 Amps pulled from AC mains (between variac and Thordarson plate transformer)
1500 Volts AC into the doubler (3 uFd Cap)
Grid leak at 15.3K (50 mA DC into grid)
16 Inch Spark:
11 Amps pulled from AC mains (between variac and Thordarson plate transformer)
1550 Volts AC into doubler
Grid leak at 13.5 (60 mA DC into grid)
The plates on these tubes do run hot, and I do not think they will take
much over volting, but performance is good for a 300 watt rated tube IMO. I
would be interested if anyone else has done such tests using the level
shifting technique vs straight AC to the plate.
Many see tubes as a poor and ineffient way to get sparks, but the power is
not wasted IMHO, I have melted nails with the output on tube coils. I think
the clue to really long tube coil sparks and power efficiency is in John
Freau's pulsed tube coil experiments.
Regards,
David Trimmell