Re: tank circuit of VTTC

["Bert Hickman" <bert.hickman-at-aquila-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Tesla list wrote:
> 
> Original poster: "sundog" <sundog-at-timeship-dot-net>
> 
> Hi Herwig, All
> 
>   I'm no MMC expert, but that amperage sounds *really* high for a single
> string.  is it RMS (I'd hope not!), or just peak?
> 
> -----Original Message-----
> From: Tesla list [mailto:tesla-at-pupman-dot-com]
> Sent: Wednesday, August 16, 2000 10:15 AM
> To: tesla-at-pupman-dot-com
> Subject: tank circuit of VTTC
> 
> Original poster: "Herwig Roscher" <herwig.roscher-at-gmx.de>
> 
> Hello VTTC builders!
> 
> I'm trying to build a dc-CW-VTTC with a tetrode. Some tube data
> for use as oscillator: peak dc plate voltage 20 kV, peak cathode
> current 12 A, average plate dissipation 1000 W.
> 
> As I couldn't find a suitable plate transformer, I tried to use a 6-
> MOT PSU providing 5600 Vdc. The problem was that the current I
> could get was not sufficient at all. I'll revert to this circuit in an other
> post. Now I've acquired a 3 phase tranny (weight 48 kgs) from a
> Russian mobile radar which, after rectification of course, deliveres 9
> kVdc and more current than I'll ever need.
> 
> The VTTC works well but the primary gets hot within short and the
> ceramic rf-type caps burnt already. So I've to redesign the tank
> circuit. I'm intending to use PVC insulated AWG 8 for the 130 µH
> coil and a MMC for the 2N2 tank cap. It will consist of 1 string of 20
> Wima FKP1 2000 Vdc 47 nF caps with bleeders and the max
> current will be 235 A. Does this design sound good?
> 
> Any comments are very wellcome.
> 
> Herwig

Herwig,

You will most likely need to go to commercial mica transmitting
capacitors to handle the current and voltage. If you choose to go the
MMC route, you will need to construct it with a large number of strings
in parallel to handle the tank current. Your primary WILL get hot, since
the circulating current will be continuous, and skin effect will
constrain the current to a shallow layer. Silver plating will help, but
you may be forced to go to water cooling. Another alternative to the MMC
may be a water-cooled commercial induction heating capacitor. 235 amps
is a lot of RF current... :^)

-- Bert --
-- 
Bert Hickman
Stoneridge Engineering
Email:    bert.hickman-at-aquila-dot-com
Web Site: http://www.teslamania-dot-com