[TCML] Handmade Vacuum Tubes Video: Build A Better 811A Mousetrap?
Sfxneon at aol.com
Sfxneon at aol.com
Fri Sep 12 08:25:05 MDT 2008
In a message dated 9/12/2008 8:13:58 A.M. Central Daylight Time,
jimlux at earthlink.net writes:
Sfxneon at aol.com wrote:
>> Hi Dave,
>> That's a mighty ambitious what if! Certainly not impossible, but it would
>> more of a learning experience than a new source for 811's. Not only is
>> glassworking part fraught with a lot of not-so-obvious difficulties, but
>> getting and keeping a good enough vacuum inside the tube during
>I don't think it's all that tricky.. Anyone who's worked with high
>vacuum systems has probably dealt with all the elements needed at one
>time or another, and, in fact, a lot of the pieces are available from
>places like Duniway or JK Lesker.
Hi Jim, all,
I just don't want people to think that reaching a high enough vacuum for
electron tubes is as simple as just pumping the air out. It's doable, but as you
mention it involves cold traps, diffusion, turbo-molecular or drag pumps,
baking out the envelope while under vacuum, and an induction heater for firing
the getter. You can build some of the equipment if you are familiar with
vacuum systems and very good with your hands, otherwise _high_ vacuum equipment is
>The art is in getting high performance...
>you WILL need some form of really high vacuum, but I suspect that some
>form of simple sorption pump cooled with LN2(see, e.g., The Amateur
>Scientist) followed by a suitable getter would probably work. Fooling
>with a diffusion pump is best left for folks running a factory, and
>turbomoleculars are for those with lots o'cash or very good scrounging
Silicone oil diffusion pumps are actually the simplest and cheapest
(relatively speaking) type of forepump, but of course they have to be backed by a
good mechanical pump. I use one of these on my neon pumping bench, and once they
are set up, they function well without much further attention. However,
you'll still need to use LN2 traps or sputter pumping to get in the necessary
vacuum. But for electron tube vacuum levels, a turbo or drag pump with LN2 traps
would be a better choice, although they are very fragile.
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