[Milsurplus] Why "Noodling" About Sweep Tubes?

[Richard Brunner]

There is merit in investigating sweep tubes as a 211 substitute. Tie all 
the grids together, put about 500 volts on the plate, put variable bias 
on the grids and see what kind of triode you've invented.  Also review 
the literature for grounded grid amplifiers, as pentodes are often used 
as a triode with all the grids grounded. Note that some tubes must have 
a resistor in series with the first grid because it will hog too much 
grid current, with bad results.

Richard, AA1P


-----Original Message-----
From: milsurplus-bounces at mailman.qth.net [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of David Stinson
Sent: Tuesday, October 22, 2013 6:36 AM
To: milsurplus at mailman.qth.net
Subject: [Milsurplus] 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