[AMPS] PL 172

[Alek Petkovic]

Hi all,
          The specs for the PL-172 or 8295A are listed in nearly all ARRL
handbooks since god knows when. Look in the Tetrodes/Pentodes Table and
from memory it is listed just after the 4CX1000A.

It is used in transmitters made by Technical Materiel Corporation many of
which are still in use today. Look at the WWV site photographs. All their
transmitters have the PL-172/8295A in the driver stage. The driver amp is
a 6CL6 into a 6146W into the PL-172 running class AB1 with about 2KV on the
plate, 500V on screen, around -100V on the grid (to give 200mA idling) and
a grounded suppressor grid. I don't know what they run in the final output
of the transmitter.

I know this because, here in VK6 we have about a dozen of these Driver
stages modified as amplifiers for our ham shacks.  We bypass the first 2
stages and put a 50 Ohm dummy load  capacitively coupled to the grid and
run the thing in AB1 with 100Watts input. We generally run about 3.3KV no
load on the plate and consequently get our 1.5KW out with the full 100Watts
drive.

The RF deck is built to last with a big mother bandswitch, Silver plated
tank circuit  and vacuum variables with nice counters for both tuning and
loading.

As far as tube swapping is concerned, you won't find anything similar
anywhere. Some guys have substituyed 4CX1500's but, as somebody said on
this reflector already, it's a lot of work.

I have one spare PL-172 tube which has full output but has some sort of
intermittent internal arcing problem. If anybody wants to take a risk on
it, give me a shout.


Hope some of the above info is of some use or interest.

73 de Alek. VK6APK

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