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Re: [TCML] Handmade Vacuum Tubes Video: Build A Better 811A Mousetrap?
You're right, that's an absolutely astonishing video! Making your own tubes
... !
And it makes me wonder...
... What if we made a power triode with high power ratings for ourselves?
I'm actually not kidding after seeing that video.
I know from direct vacuum tube experience that 811A-based Tesla Coils are a
great deal of fun.
I'm a little concerned that the 811A's available now, especially from
Russia, suffer from quality control, because I've seen their plates go red far
faster than US-built equivalents, and I've seen plates melt unexpectedly quickly.
But the French HAM radio operator in the video building his own tubes is
obviously running off qty 20 at a time. (You see him building inner parts 20 at
a time)
If he can do that for tubes which are small and complex, and look something
like 12AU7's rough size (and please, I'm using the word "rough" here; I know
a 12AU7 is pretty complex), and he gets some use out of them in his HAM rig
... well ...
Why can't we make some power triodes? Let me draw an analogy here on what
they might be like.
Do some early tries the Soviet Way: Bigger And Clunkier.
Like this: Heck, when you started up the older model Soviet tanks, you
expected to gather a full kilogram of engine shavings in the engine oil during its
first run, because the tolerances were so sloppy. You have to change that
oil before moving on.
The 811A's were a design from the 1930's. (My old datasheet was copyright in
the 1930's). We don't have to match their "form factor" (their size and
shape). They have 4 pins -- 2 for filament, 1 for grid, 1 for plate. Filament is
6.3 volts @ 4 amps. We don't have to match that, either. We can make
something far clunkier that isn't designed to have all the smooth characteristics of
a transmitter tube made for Class A, B, and C operations. We're not going to
be broadcasting voice through this.
What we need is something that will accept an input at the grid around 90
volts (100 V max) at 50 ma, max, to modulate a plate voltage of around 1200 to
1500 volts max, switching on and off a current of 130 ma to 160 ma max. This
is around a 160 Watt tube (max).
[A lot of the 811A specs are specifically for two-tube systems; pretty much
double the above figures, except plate voltage. Many 811A circuits are
push-pull and so forth.]
There are also better metals and alloys than there were in the 1930's
(obviously).
Most of the rest appears to be professional grade glassblowing, and I know
very little about that, so I'm smart enough to assemble the tube innards and
let pros encase it in glass and evacuate it. (And possibly not glass if a
stronger material would work.)
My question for the List is this: What characteristics of the 811A should
be improved upon? For example,maybe we should put a physically stronger plate
in there that won't fail so quickly if it is heated to red. Do we need more
current carrying capability? Then it needs a better anode and grid. I might
have to blow dust off the books, but vacuum tube design is very well documented.
This might be really interesting.
Thanks,
Dave Small
******
In a message dated 9/9/2008 6:31:47 P.M. Mountain Daylight Time,
Sfxneon@xxxxxxx writes:
If you are really into hand building everything that goes into your in your
VTTC, then how about making your own tubes like this guy:
_http://blog.makezine.com/archive/2008/01/make_your_own_vaccum_tube.html_
(http://blog.makezine.com/archive/2008/01/make_your_own_vaccum_tube.html)
(http://blog.makezine.com/archive/2008/01/make_your_own_vaccum_tube.html)
Long, but well worth it!
Tony Greer
**************Psssst...Have you heard the news? There's a new fashion blog,
plus the latest fall trends and hair styles at StyleList.com.
(http://www.stylelist.com/trends?ncid=aolsty00050000000014)
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