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RE: Re: tank circuit of VTTC
Hi,
Comments interspersed:
On Thu, 24 Aug 2000, Tesla list wrote:
> Original poster: "Herwig Roscher" <herwig.roscher-at-gmx.de>
>
>
> David Trimmell wrote to the list:
>
> > Again, with up to 3 833C's filted DC 2+ KW in.
>
> David,
>
> Thank you for your comments. I copied your schematic and I've got
> some questions:
>
> 1. In my records I found the 833 A to have a plate dissipation of
> 300 W at natural cooling and a maximum plate voltage of 3000 V.
> Does the 833 C offer better data?
>
..................................................
See http://216.36.6.9/webdoc2.htg/Tube_coil/833a.zip for 833A info. Dave
Sharpe recently posted to the list a table of data for 833A,C,D, can't
remember exactly the values, but the 833C is around 400 Watt. I use a
3small muffin fan pointed at the tubes and primary for cooling on extended
runs, will probibly rig up a better system in the future. The C has
Graphite plates, making it more robust. But I have used the A's also.
..................................................................
> 2. Do you use forced air cooling for your MMC?
................................................................
Nope, but It wouldn't hurt.
...................................................................
>
> 3. Plate voltage: Do you use a variac permanently and is your plate
> voltage 5 kV? Are there any arcovers *in* the tubes as the rated
> max voltage is 3 kV only?
....................................................................
Yes! A variac is esential. I have run the 833's up to 5500V (in Staccato
mode, ie. pulsed 1-30 PPS) without internal arcover.
.......................................................................
>
> 4. Is there any rf bypass for C1?
.......................................................................
Not sure of what you mean? All grounds are a common RF ground, so the
filter cap should bypass most RF to ground. I use a couple very robust
transformers, so I am not greatly concerned about a little RF getting
back. And my diodes are series strings of 1KPIV six amp.
.................................................................
>
> 5. Did you have a look at the generated wave form? Is it a pure
> sinus or is it distorted?
..................................................................
Yes, I scoped RF output using a small antenea on a 10X probe. With at
least 6uF filter cap, output is smooth, very little ripple. Currently I
have a 16 uF filter cap, seemed to improve audio slightly.
.......................................................................
>
> 6. In the schematic your tank coil is not tapped. How did you
> manage the tuning?
.........................................................................
Let me apologise, my schematic still needs some work, values are from
memory, not notes. I designed the MMC to give me a "close" value, and can
tap up or down the string, not perfect, by far. Inductance is measured and
so is capacitance. Also for fine tuning, one can add/remove capacitance at
the discarge terminal.
.........................................................................
>
> > if you go and use a larger diameter pri conductor, then you may
> > run into problems with size.
> - The coil would become very bulky if I used e.g. 1/4" tubing.
>
> > MMC is a single strand of Panasonic 0.015 uF caps, it does get
> warm, and I sugest using two strings for longer life.
> - A single strand! I'm surprised. I'll redesign my MMC if I know the
> final conductivity of my new tank coil.
.......................................................................
Here you are in new territory, I have not gone over the 5KV mark much.
.........................................................................
>
> > I generally run mine at 1.5 X Plate voltage.
> - Did you face any MMC failures because of this small factor?
>
..........................................................................
One cap exploded like a fire cracker while only using 4-5 (up to 3500V) in
series doing some crazy experiments. Pulsing the coil (out of tune!) with
the RC timing in the grid leak, Sputter mode.
.......................................................................
> > 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
> dutycycle down.
> - That's interesting for my next step towards audio modulation.
>
> > I did "burn" up a secondary once, it seems to get the hotest af
> anything (besides tubes
> - Could you please recommend a "burn-proof" :-)) 4" secondary?
>
......................................................................
Have to dig up the photos of it an put them on my web site. Just watch the
temp and perhaps forced air (from bellow) would be good. The coil had been
running for some 30 minutes, or so, and I had failed to monitor temp. Live
and learn ;-)
Regards,
David Trimmell
www.ChaoticUniverse-dot-com
.................................
> Regards,
>
> Herwig
>
>
>
>