Re: tank circuit of VTTC

["David Trimmell" <davidt-at-pond-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hey all, Bert,

This has really got me thinking. Last night I hooked up my coil, with the
Audio Mod setup, and got it working ok (My Cisco DSL router/bridge sure
didn't like it, I'd loose the WAN connection every time I fired the coil).
So as time will permit, I am going to do some testing. My original single
string MMC was not expected to last this long, granted, I have not placed
full power (5KV filtered DC) on it for any great time, as tubes don't like
going over 4KV much. When opperating Filtered DC non-Audio mod mode, I use
9-12K resistance in the grid leak as less will cause the grid current to
go over 300 mA.

I hate it when theory and reality seem to clash. There must be a reason.
One thing I know, is that I have opperated these MMC's well beyond their 3
amp limit (RF?) for some time, with no apparent harm. In fact, I run them
at 2700V in Audio Mod mode for, probibly several hours run time. Thats
over 10 amps RF, but with 40-50 k in the grid and Audio, the duty cycle
must be low??? Sugestions anyone?

Thanks,

David Trimmell
www.ChaoticUniverse-dot-com


On Thu, 24 Aug 2000, Tesla list wrote:

> Original poster: "Bert Hickman" <bert.hickman-at-aquila-dot-com> 
> 
> Tesla list wrote:
> > 
> > Original poster: davidt-at-pond-dot-net
> > 
> > Hello,
> > 
> <SNIP>
> Bert:
> > I'd suggest beefing up the tank circuit by going
> > to
> > larger diameter copper tubing or flat copper strap, and possibly
> > silver
> > plating it as well. You are likely going to melt the PVC insulation
> > on
> > your primary under extended running conditions.
> > 
> > ..............................................
> > 
> David:
> > Well, I would have to take issue with this. I have used #12 PVC
> > insulated wire on my primaries without any problem. Again, with
> > up to 3 833C's filted DC 2+ KW in. "I" believe #10 would be fine,
> > if you go and use a larger diameter pri conductor, then you may
> > run into problems with size.
> > 
> > ...............................................
> 
> <SNIP>
> Bert: 
> > However, I have no doubt that a properly constructed MMC could
> > safely
> > handle this task. 
> <SNIP>
> 
> > .........................................
> David:
> > Sure can. Been, there, done that. My current MMC has been in
> > use for over a year and a half, with many hours of run time (I
> > have used my Audio Mod Vac coil for mood music in my shop while
> > working on other projects ;-)). MMC is a single strand of Panasonic
> > 0.015 uF caps, it does get warm, and I sugest using two strings
> > for longer life.
> > 
> > .........................................
> > 
> <SNIP>
> Bert:
> > However, there's not very much empirical experience with the
> > long-term
> > performance of MMC's in a CW RF environment...
> > 
> > .....................................
> David:
> > Like I said: I'v been running them for over a year and a half.
> > It is very true that while running with just filtered DC everything
> > gets hot after several minuts, I would not recommend running
> > a setup like mine (#12 pri, single strand MMC, 2-3 388C's -at-5KV)
> > for more than 2-3 min runs, on filted DC alone. I must point
> > out that the meathod of Audio modulation I use (grid), I run
> > the tubes at almost cutoff, with 40-50K Resitance in the grid
> > leak, and the effective "pulsing" of the tube must cut the duty
> > cycle down. That must be how I can get 10 to 20 minute runs (
> > not full power with longer runs, of course). I did "burn" up
> > a secondary once, it seems to get the hotest af anything (besides
> > tubes ;-)). My Schematic can be seen at:
> > http://216.36.6.9/webdoc2.htg/Tube_coil/Audio_mod_sch_sm.jpg
> > 
> > Regards,
> > 
> > David Trimmell
> > www.ChaoticUniverse-dot-com
> <SNIP>
> 
> David,
> 
> Thanks for the additional information! At 10 kV plate voltage, the
> design that Herwig was proposing would have subjected his tank inductor
> and capacitor to about twice the RMS current of your system (if running
> flat out at 5 kV). And, all other things being the same, this would
> result in 4X the amount of joule heating in his tank circuit. 
> 
> I am very surprised that you are not seeing substantially greater
> heating in your tank circuit. The high value of grid leak resistance
> used in your system (40k versus 1-3k typical) may be reducing the
> overall RF amplitude seen in your tank circuit. If you were indeed
> running at about 15 A RMS RF (running flat out at 5 kV plate voltage in
> your system), I would expect your single string tank cap(s) would get
> VERY hot. The Panasonic MMC caps showed almost a 20 degree C.
> temperature rise when carrying only 3A RMS current in Terry's earlier
> experiments. If your system WAS actually hitting 15A RMS at almost 400
> kHz, that's 5X the level that Terry was running, and it would imply at
> least 25X the joule heating that Terry saw. Your single string of caps
> would NOT survive this type of abuse for any length of time. 
> 
> This is really a poser...! 
> 
> -- Bert --
> -- 
> Bert Hickman
> Stoneridge Engineering
> Email:    bert.hickman-at-aquila-dot-com
> Web Site: http://www.teslamania-dot-com
> 
> 
> 
>