[ARC5] Why "Noodling" About Sweep Tubes?

[Geoff]

----- Original Message ----- 
From: "David Stinson" <arc5 at ix.netcom.com>
To: "ARC-5 List" <arc5 at mailman.qth.net>
Sent: Tuesday, October 22, 2013 6:36 AM
Subject: [ARC5] Why "Noodling" About Sweep Tubes?


> 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.
>
> 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.   Of the few that remain, some are low-emisson 
> and will work only in the oscillator stage.
> 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.
>
> 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.
>
> Did something similar to this with the SCR-183 tranmitters-
> another one that is too expensive for most to use original tubes.
> Mounted some little audio pentodes (triode connected) in socket adaptors
> and it worked well. Hoping for similar success with the 375.
>
> 73 DE Dave AB5S


There arent any single ended choices in the 211 base that arent as 
scarce/expensive.
Sweep tubes or any other tetrode/pentode has its own problems with internal 
C values much different which might require some serious mods to work.

Have you considered 811A's ? They might be the least troublesome and are 
still readily available.

Carl