Hi Steve,
I work second shift, so a bit of a delayed response.
Yes, I still do not do taps. So yes currently tune with a combination of
the variable cap and grid adjustments. The initial rough tuning of the tank
was done by rough calculations for a starting point, then running and for
this setup, I added by temporary jumpers, more and more capacitance as
needed. I make big changes, then when I realize too much, back off some,
then do smaller amounts. Took notes and then determined the final amount
needed for the fixed micas in the tank also figuring in the variable cap to
give me range both ways. And this also is done in conjunction with
resistance changes in the grid pretty much at the same time...
Yes, doing this was part of the goal in improving efficiency. I also did
very efficient connections for the caps. Metal deck support/connections on
bottom side. Flat silver plated copper strap on top, no sharp bends.
Yes, no form. I feel this also helps in reducing losses. And I thought it
would look, well "cool" and "naked". Think I have achieved this, but the
original intent is to reduce losses. I was maybe just a little concerned
about arcs, but not really. And I am happy to report, no arcs.
I want to mention here, that the inductance is really low here for
especially a tube coil, considering the "traditional" route taken by most
for VTTC's including me until now. But this is also of course spaced turns,
being bare copper, so also obviously spreading this coupling over a larger
area.
Off the top of my head right now without looking at some notes, just 9uH
approximately in those about 13 turns was measured. The 3 fixed micas
totals to about .018uF. Not sure where the vacuum cap is set currently.
As I said, this ratio is normally advised against from what I have read in
the past on tube coils. But I think there is also some differences here
because of spaced turns, very low resistance, low losses, and being pulsed.
A least for me here with this setup, the tube is handling this just fine.
I thought I was running efficient before this, but it is in my eyes
extremely efficient now. Did slight double takes looking at the input amp
meter at times, especially when I turned the break rate way up. Very little
increase amp wise. Before, the starting amp draw at lower rates was very
efficient, but it would climb accordingly as the rate went up, and when way
up, became a considerable amount, which to me was normal, more power
required, and well more losses also.
I will this weekend be testing more. Too busy with work during the week. I
will get some numbers here, take some pictures and video of it running and
will also show the input amp meter at various different rates on video,
showing how stable it is and well how low the draw is.
So I am glad I have tried this, as I said, I have been wondering for quite
a while now. I guess you can say I am surprised, but not completely
surprised. Still, it has exceeded expectations.
Ok, enough of my rambling here... sleep time...
Chris Reeland
Ladd, Illinois, USA
Sent from my LG V20
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