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RE: [TCML] Dual-triode VTTC (811A/812A)?
Thanks for the information. I suppose this settles it - I'm going for an 811A&812A push-pull arrangement.
By the way, it's more like multiplying your input voltage by 1.5, since the second half of the wave helps to de-saturate the transformer (make the magnetic field collapse), though the on-time is severely limited due to the risk of the tubes/transistors being on at the same time. This is, of course, in a transformer-switching topology and not a Tesla coil topology, where peak amps = ~ peak efficiency. In a transformer-switching topology, you want your on-time to be as long as possible, though, when single-ended, you run a risk of over-heating your transistors with excessive on-time and, for that reason (as well as others), can only have them on (reasonably) for about 0.5-0.75 duty-cycle. ;)
- Christopher Karr
> Date: Wed, 12 May 2010 09:33:03 -0500
> Subject: Re: [TCML] Dual-triode VTTC (811A/812A)?
> From: steve.ward@xxxxxxxxx
> To: tesla@xxxxxxxxxx
>
> The only thing id worry about (and this is an un-educated worry), is that
> because of the gain mismatch, you may end up needing to use different grid
> feedback windings (or a tapped winding). At least in the power-conversion
> world, a push pull drive must be *really* well matched, or you risk
> saturating the transformer you are driving because of the slight "DC" bias
> that having non-symmetry will provide. Obviously a VTTC is air core, and
> cant saturate, but you might still end up with something out of balance,
> though im not sure to be honest. If i had to guess, it would end up
> stressing one tube more than the other.
>
> BTW, my 811A coil (and any of my VTTCs) were never push-pull, always just
> single ended oscillators. Push pull is a good way to go if you dont mind
> the extra complexities, its sort of like doubling your primary drive
> voltage.
>
> Steve
>
> On Tue, May 11, 2010 at 9:26 PM, Christopher Karr <chriskarr4@xxxxxxxxxxx>wrote:
>
> >
> > My thoughts, exactly. My question is this: would it certainly work?
> >
> > - Christopher Karr
> >
> > > sure that would probably work.
> >
> > > On 5/9/10, Christopher Karr <chriskarr4@xxxxxxxxxxx> wrote:
> > > >
> > > > Hello everyone,
> > > >
> > > > I was curious as to whether or not a pair of vacuum tubes which are not
> > > > matched (811A and 812A, in this case) might be usable in a
> > push-pull-type
> > > > VTTC (such as the dual-811A VTTC on Steve Ward's page). As far as I can
> > > > tell, the only major difference between the two is the gain, though the
> > > > rated drive-power, drive-voltage and output-power (as well as
> > dissipation)
> > > > are equivalent.
> > > >
> > > > If this isn't a possibility (or there's a likelihood of near-immediate
> > > > failure), may I ask why?
> >
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