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Re: [TCML] Rebuilding VTTC

Hi Terry,

"I probably should have known this 0:D"

> I was kind of wondering...  :^)

> "Yes!  My old 811 tubes automatically installed cooling vents into
> themselves... :D"

> I did this to a fairly old single RCA 811 from around 1939-40, if my
> memory is correct. This accident happened to me in the mid 1980's if I
> remember correctly. My current single 304er coil has formally been a single
> tube: Cetron T-200, Cetron 572B, RCA 811A, and to start originally, a RCA
> 811 in the early 1980's. Was quite bummed at the time. These 811's and well
> 811A's (a redesigned new version introduced not too long later, with
> several horizontal anode fins) are not very tolerant to overload conditions
> for very long at all, hence a quite common problem of "discoloration spots"
> or worse the "cooling vents" if not careful or poor tuning which involves
> so many numerous things. The zirconium coated molybdenum anode material is
> prone to this on these tubes and well other tubes. They are just fine if
> you keep overloads in check. But VTTC's can definitely present quite a
> heavy load. Have seen a few 833A's (a quite popular VTTC tube) suffer this
> also, hence some then aquire a graphite version of the 833A. Not all tubes
> have a graphite equivalent available.

The previous T-200 I ran, has graphite anode. And well you know, so does
> the 572B have graphite. My current Eimac 304 has a tough tantalum anode.
> This 304 is a pre WW2/very early WW2 tube. During later WW2 it was then
> changed to zirc/moly by Eimac. Tantalum is quite more expensive and even
> more during the war, hence the change during and even after the war by
> Eimac. Actually there was not very many makers Tantalum types to begin with
> on transmitting tubes before the war. And zirc/moly was actually still
> pretty new itself before the war by many tube makers, if I remember
> correctly. Zinc/moly was an improvement over other metal types at the time
> for transmitting tubes. And graphite had been out for a while before the
> war also competing with metal types. There are also some pluses and minuses
> graphite vs. zirc/moly. If you can not tell...I am a bit of a "tube geek",
> especially transmitting tubes. Interested in their history/design
> changes/improvements/actually using them... :^) I think the majority I said
> here is pretty correct. Going from memory on so many different things I
> have read online and my collection of all kinds of tube data books and
> handbooks.

Here is a picture of my "cooling vent" 80's tube coil mishap :^)
I have on this coil always been a single tuber, instead of a pair to share
> the load. I like to see what I can achieve with one on this coil.
> Definitely can be more challenging at times. Been quite a few power supply
> changes over the years also. Currently a MOT also, was not intended
> originally at all, but that's what happened....  In your setup, the even
> better 572B pair, is the minimum "size" tubes, mandatory for your power
> supply in my opinion. Otherwise, larger more powerful tubes required. The
> pair of Russian Svetlana 811A vertical fin tubes actually did not have
> much of a chance here in my opinion in this set up, especially if poorly
> tuned. The graphite heats up much more evenly as possible to dissipate this
> more efficiently, besides withstanding the temperature overloads better and
> for longer. Still there are limits to everything. Eventually the tube pins
> seals can possibly come into play if graphite extremely overheated and the
> tube will lose vacuum through those seals being overheated.

> "I bought this coil like 20 years ago on Ebay and it has always worked
> very well.  But I really don't know how it works so I thought I would fix
> it up and figure it out now."
> Better late than never :^)  &  :-D

> "I actually have a computer simulation of it going now."

> Interesting... still studying this some. Have not personally seen this
> kind of tube coil analysis before. Keep this coming when/if you can.

> "It's very preliminary but it sort of runs and allows me to fiddle with
> things while I learn.  After messing with the model I refined the values
> and it should actually be running at 407kHz."

Good to hear running somewhat after some recent changes. I would say
actually it was never really tuned up that well to begin with and after you
got it. Do try changing the grid leak around when you can. And you already
know to get the "tank" corrected.

"Antonio's INCA program was super useful!

I got the secondary measurements all wrong since it was installed in the
> coil and very hard to measure in place.  It is actually 800 turns of #27
> wire and the INCA program found this error right away!"

Again interesting here to see this... :^)

> "So I think I am off to a good start figuring this coil out.  :) "

:^) Glad to hear this...nice to hear about some more VTTC's.
Until recently some... kinda quiet in this realm.
Keep us updated on analysis and improved tuning when you can.

Chris Reeland
Ladd Illinois USA

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