Re: VTTC output

["Tesla list" <tesla-at-pupman-dot-com>]

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.

Ed,

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 
connected simultaneously.
- 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 
nothing changed.

> > 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 
this methode:

rectifier + ---*----------- to tank circuit
               |
            15 µF/10 kV
               |
rectifier - ---*---10 kOhms---*---*--- -
               |              |   |       analog
          20 Ohms/ 5 W        a   |       Vmeter,
               |             ZD 100 nF    range 
               |              |   |       10 Vdc
               *--------------*---*--- +      
               | 
         system ground

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 
rectifier diode.

> 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,

Herwig