"Tom Schlangen" wrote
...
As I see it, this noval based pentode intended for
video outputs is very linear in pentode mode and
when being triode strapped, too. See the Marconi
sheet, page 8, for the trioded data.

Moreover, the 300mA heater versions PL83/15A6 are plenty
and cheap as dirt at least here in Germany. Might be
very worthwhile to invest a few cents in that tube
and an LM317 for the heater CCS and have a try at it :-)

Similar to 6CH6 (EL821), but less perveant, if that's a word. OTOH
300mA is heaps more convenient than 750mA. Heater power is greater
than output power in class A for 6CH6, although that's a common
complaint I suppose.

One feature of these valves is the gentle rise in current from Vak=0
for any particular Vgk. with no clear knee. Since screen curve is
mirror of anode curve, this means that screen current can become a
problem at higher values of Vak than with the common audio beam
tetrodes.

So not so suitable for CFB designs, particularly if you want
super-pentode (where Vsk is kept constant). The power advantage of
CFB is in utilising that low Vak region. Combination of high gain
and reasonable distortion otherwise make them good candidates.

I notice 6CH6 prices are rising. I should have got more...I think
they are generally of good quality.

cheers, Ian