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Re: VTTC output
Original poster: "Herwig Roscher by way of Terry Fritz <twftesla-at-uswest-dot-net>" <herwig.roscher-at-gmx.de>
Ed Phillips wrote:
> would wonder if you are running at a harmonic of the fundamental
frequency of the thing.
The natural frequency of the secondary sitting
inside the primary and tank capacitor
disconnected is about 245 kHz and the measured
oscillator frequency is about 200 kHz (nearly
pure sine). IMO(!) it's unlikely that the system
runs at a harmonic therefore.
> > The voltage across this bulb is 130 Vpp and nearly
independent(!!) on the power output.
> Gather you are running with the bulb AND the secondary
- Yes, I do so.
> Wonder if the power into the secondary streamers increases so
rapidly with increasing input power that the
system acts as a
non-linear voltage regulator, with more or less
constant primary voltage and hence induced
current into your bulb
- I disconnected the bulb during oscillation and
> > If I calculated the tank voltage from (67 turns of primary / 4
turns of pickup coil) multiplied by 130 Vpp,
getting 2200 Vpp.
> That measurement can't be right.
- Probably *this* measurement is right, because
the numbers of the turns are correct and scoping
the voltage across the (low impedance) bulb
should be no source of errors.........
> plate dissipation would be AT LEAST (7500 x 0.48) = 3600 watts.
- .............but I'm suspecting now that the
measured plate current wasn't correct. I used
rectifier + ---*----------- to tank circuit
15 µF/10 kV
rectifier - ---*---10 kOhms---*---*--- -
| | | analog
20 Ohms/ 5 W a | Vmeter,
| ZD 100 nF range
| | | 10 Vdc
ZD = 15 V power zener diode, a is anode
Because of the very sharp current pulses, the
tube draws, the dc across the 20 Ohms resistor
is superimposed by rf despite I've connected a
10 nF/20 kV cap from the cold end of the tank
circuit to system ground, bypassing it.
Trying to smooth the voltage across the 20 Ohms
resistor by 4 paralelled 0.22 µF/ 1000 V
pulse(!) caps resulted in a real explosion of
these caps. So a lot of rf is present obviously.
However, if the voltage across the tank *was*
that low, would increasing the tank impedance be
the way to go? For a perfect match, what should
the voltage across the tank be, assuming a plate
voltage of 10 kVdc? 10 kVpp?
> Better way to measure the primary voltage would be with a tube
rectifier (1B3GT .......
- Thanky you for the info. I'll look for such a
> I'm beginning to get the urge to dig out some of the high-powered
stuff in the attic and start building!!!!!
- ~~~~~~~~~~~~ a very
good idea! :-)))))
Many thanks and kind regards,