• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Those Magnificent Television Tubes

Yep, 6AR8 is another BDT. Can make it amplify too. It is a full differential stage.

Here is a little blurb on BDT tubes and the 7763 from Shea's "Amplifier Handbook".

And some pics of the back side of the 7763 tube.
 

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my bad, guys, I (as a semi-young crowds) do not have boxes of tubes in my stash, neither I have decades of experience with "those magnificients". ..<snip>
For UL usage, is possible to make a output trafo with separated screen grid windings:
https://www.plitron.com/wp-content/uploads/2010/05/2100SSCR.pdf
http://toroid.com.br/images/downloads/a83769b558525d1718640dd15f79b91b.pdf
See #TL70147
This is my baby (I designed it when I worked for Toroid do Brasil)
(of course, the datasheet have some marketing words and -6dB only graphs, but works very good).
They are expensive, so brave people will construct one.
How to make on TL70147 I don't show (unfortunately), but I can say that screen winding must closely follow the primary winding traject (for "normal" UL tap).

BTW for sweep tubes the 40% UL probably will cutoff/overload the tube prematurely due to famous high g2 gain. So perhaps 20% will be good. Easier to make.

Some specific tube #s?
I think I did see something about a micro-channel multiplier amplifier recently. Secondary emission amplification. (night vision goggles, Tek image intensifier in 7104 scope...)
Maybe something available on Epay?
Some years ago I found some russian vendors for these tubes by accident, in exploring all submenus and all products from seller. Some sellers don't identify correctly the name of tubes so is harder to find.
But I don't purchased any...

Photocathode Image intensifier tube V-8 EP33 night vision binocular goggle 1+gen | eBay
At least one found very easily.
 
Yes, 7360 was RCA's BDT. It got used for SSB in Ham radio designs. I have a small box of them. They were plentiful at one time, but have become scarce now. 6HW8 was Amperex's BDT, got a few of them. 6AR8 was Tungsol's BDT. 6JH8 was GE's BDT. 6ME8 another GE one. All of these are relatively plentiful, and all are similar to low Mu triodes over a CCS tail. I would say 6JH8 is the most practical one, and most plentiful, operates with deflectors at 0V DC.

No problem making them into a splitter. These also got used as voltage controlled gain controls (so remote control possible). These tubes can be easily configured to do analog multiplication too, using 3 of them in a tree configuration for highest accuracy. (they were used that way for SSB generation) They would have been the start of the next generation of tubes if SS had not come along. Many other related designs were in the research journals of the time. The beam deflection mechanism is a linear process (constant gm) as opposed to the 3/2 power process with conventional grids.

The available BDT tubes are not well suited to power stages, however, unless you have a lot of them. (I got a box of 330 6JH8s cheap during the sale days. A massive OTL? 6 Watts Pdiss per tube. Well a dozen tubes with an OT would be practical. Like two 36 Watt tubes.) Research BDT versions were approaching power capability in the journals. Since we have Twin/Crazy drive now, conventional Sweep tubes can fill that constant gm power role. Imagine a tube amp built -entirely- of linear gain devices.
The proverbial "wire with gain".
 
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looked at the 954 pentode?

The 954 pentode was a WWII attempt at raising the maximum operating frequency of a conventional (non planar) vacuum tube by shrinking the guts. Of course this also reduces the voltage and power that can flow through it. It is basically a shrunken 6AK5 (5654) tube. There is a 7 pin miniature version, the 9001 that shares the same pinout as the 6AK5. I have some of those around here, but don't remember anything special about them.....maybe I'll try them again when I get back to ultra high gain circuits where microphonics become a problem.
 
Here are some triode mode curves for (the pentode of) a Montgomery Ward USA 6LU8 tube (looks like Sylvania construction, but measures closest to a GE 6LU8 I have)

Vertical 20 mA/div, Horiz. 50V/div, Grid1 4V steps down from 0V

I measured a Sylvania tube and was similar except 7% less Mu.
I measured a GE tube and was nearly identical.
I measured an RCA tube and that had higher Rp (the grid 1=0V line at 200 mA was at 150V plate instead of near 100V plate for the others.) Noticeable roll-over in the curves too. If the other 6LU8 RCA tubes I have measure like that, I'm throwing them all out.
 

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