Re: The Quick and Dirty VTTC

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Dr. Duncan Cadd by way of Terry Fritz <twftesla-at-uswest-dot-net>" <dunckx-at-freeuk-dot-com>

Hi Folks!


Yet another update.  Ulrich and others apparently had problems with
the rf choke (100uH rated 1A) in the design on his webpage and it
seemed that this component might be a little critical.  I have done
some investigating . . .

My original choke was 164uH and had a self-resonant frequency of
7,3Mc/s or so.  You'll recall the total HT current was 154mA.  Well,
what puzzled me was this choke got warm!  We are talking 1,6mm wire
here!  I thought after a while that the fact that the frequency of the
VTTC is 29Mc/s might mean there was a 4th harmonic current in the
choke and hence a couple of current maxima.  Also, maybe the reason
that the choke specified by Ulrich worked and others didn't could have
been that this part was self-resonant at the operating frequency.  So
I wound a second TC to the same dimensions as the first, and despite
it being a mere 10uH, this component works perfectly as the plate
choke :-)  It also remains stone cold!

So if you're building the quick & dirty VTTC to Ulrich's design and
can't seem to find the right choke, just wind two TCs instead of one
and use one of them as the choke - end of problem!

It also does occur to me that effectively what we have here is a
half-wave coil fed at the centre with one end earthed . . . violin
bows and vibrating strings anyone ?

Dunckx