Re: tank circuit of VTTC

["Herwig Roscher" <herwig.roscher-at-gmx.de> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Bert Hickman wrote to the list:

> In that case we need a bit more information to properly answer 
your question:

Bert,

Thank you for your patience.

> - Planned plate voltage?
10 kVdc. If this caused problems I could use 6 kV as well.
Some tube data for use as grid pulsed oscillator: peak dc plate 
voltage 15 kV, peak cathode current 12 A, average plate 
dissipation 1000 W
 
> - Planned tank circuit C and L?
2.2 nF parallel 130 µH. L/C ratio is rather high as tetrodes like 
higher load impedances than triodes.
 
> - Planned duty cycle (are you planning to drive from half-wave,
> full-wave, or filtered DC)?
Pure dc (filtered by one or some 15 µF/10 kVdc cap) as I'm 
planning on trying audio modulation. I've acquired a 3 phase HV 
tranny from a mobile russian radar that will provide more power 
than I'll ever need (weight 51 kg).

> - How many strings of caps will be connected in parallel?
1 string of 20 WIMA FKP1 2000 Vdc, 47 nF caps with dv/dt = 5000 
V/µs
 
> Assuming you're running in class C operation the peak-peak RF 
voltage on your tank cap can be 2X the applied plate voltage, and 
the peak circulating tank circuit current can be as much as 
Vplate*Sqrt(C/L).  
- So, 40 kVdc and 235 A (I peak) for the cap should be ok? And 
AWG 8 is an overkill and AWG 10 is sufficient?
 
>Unlike a disruptive coil, a VTTC typically has a much higher duty 
cycle... as much as 100% in the case of a system driven off a 
filtered DC supply. The combination of high RF RMS currents and 
high duty cycle make your application a potential capacitor killer, 
especially as you begin to increase plate voltage.
- I've stated this already burning some ceramic rf caps.
  
> Flimsy leaded caps need not apply for this job... :^)
- Usually I'm wiring my MMCs with thick leads, but the internal 
wiring of the caps....????

Regards 

Herwig