[ARC5] Why "Noodling" About Sweep Tubes?

[Kenneth G. Gordon]

On 22 Oct 2013 at 5:36, David Stinson wrote:

> Some people have asked why I'm thinking about sweep tubes and 
> the BC-375.  I do use 211s in my personal rig. 
> However, there are a lot of 375s sitting around because 211s 
> have become so expensive. The least expensive I've seen are 
> the Sino chinese, which are going about $75 each. 
> $300 to get the old beast going is too much to ask for most people.

Hmmm...well, I don't know how things are on eBay concerning 211s now, but 
a few years ago, by VERY careful shopping, I managed to buy quite a few 
211s (or VT-4Cs) on eBay for an average price of $20.00. I shared most of 
them at my cost with other folks who needed one or more. I kept two and use 
them in my own P-P 211 TNT 1929 transmitter.

> Worse- I finally got around to testing the big stash of 211 tubes I've
> been accumulating for years.   Much more than half of them were bad-
> most from gas.

As you know, some of those can be reactivated by any of at least three 
different methods. Their filaments are thoriated-tungsten, after all. Some of 
such tubes simply need to be "re-gettered".

>   Of the few that remain, some are low-emisson and will
> work only in the oscillator stage.

Low emission is about the easiest thing of those that can be wrong with 
tubes to fix.

> This much-reduced stash is going to
> have to last, since 211 prices aren't likely to come down. So I'm
> trying to find an affordable substitute, not only to "stretch" my tube
> supply, but in hopes we can get some of those 375s off the garage
> floor and back among the living.

Good project! I'd love to have a 375/191...if I had the room.

> Sweep tubes with less-popular filament voltages, like between 10-14,
> are not nearly as expensive.  They are good for high voltages and
> currents. But I don't know enough about them to "narrow the field."
> Thus, my appeal to the group's wisdom and experience.

OK. Let's go to work to see what we can do here, folks.

Ken W7EKB