Rich wrote,
>
>I doubt that the tube has been damaged. The grid is way more rugged than
>the grid in a 4cx1000A. . I would be tempted to operate the tube in
>Class AB1, grid-driven, Scott. Even if some way could be devised to
>operate the PL-172 as a high Mu triode, cathode-driven tuned inputs are
>not a piece of cake. Grid-driven tuned inputs are. .
>
Rich is right on the mark. Conventional is best.
Over here in VK6, quite a few guys are running the 8295A/PL172 pentode in
class AB1 grid driven. We got the rf decks from the Yanks when they moved
out of the North West Cape communications facility over here. They are the
intermediate power amp stages from the 20KW transmitters made by the
Technical Materiel Corporation of Mammaroneck New York. Beautiful stuff.
Big and all silver inside.
Vplate = 3200V
Vg1 = approx -110V (for 200mA idling current)
Vg2 = 500V
V supp = 0V (determined by the variant of the SK184 socket. Ours are
grounded, others are floating to allow for +35V to be connected.)
A 50 Ohm dummy load close to the grid gives us a very good match into the
amp and allows a 100W radio to drive the amp nicely without exceeding the
control grid into the positive region.
Typical output under these conditions is about 1.2 Gallons. We reckon
that's quite adequate.
In other words, forget your fancy configurations and stick with the tried
and true. It's usually simpler and there's probably less to go wrong.
73 de Alek, VK6APK
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