The need to add my $0.02 to this thread has become overwhelming. So here is
something that at least a few of you might appreciate.
I copied this chart out of a book some 25 or 30 years ago. I don't recall
the title and recently a search failed to find said book in my library. No
matter, I made copies of this chart and keep one in my desk at work, one in
my shack file, and one posted next to the TP dispenser in the head.
Those of you who are clever enough to keep your email software set to
display a fixed font may actually see this in table format.
TUBE Ep Ip Cathode ohms
811A 1250 175 320
1700 160 320
572B/T160L 2400 250 215
813 2000 200 270
2500 200 270
3-400Z/8163 2000 400 120
2500 400 120
3000 333 120
3-500Z 2000 400 115
2500 400 115
3000 370 115
3-1000Z 2500 800 65
3000 670 65
3500 750 65
3CX1000A7 2500 875 41
3000 800 42
4-125A 2000 105 340
2500 110 340
3000 115 340
4-400A 2000 265 160
2500 270 150
3000 330 140
4-1000A 3000 700 104
4000 675 106
5000 540 110
Subject to any typos I may have made, this is an abbreviated version of the
chart I copied many years ago.
Obviously the tetrodes are Triode-Connected-Grounded-Grid. The only claim I
can make is that the data has been spot on for all the tubes I've tried.
It's so close that I no longer put adjustments on the components in the
cathode pi-net.
By the way, leave the damn tube in the socket when you measure the network
match. Why tack in a cap to synthesize the tube capacitance when you have
the real thing. Besides, why put more wear on the socket contacts. I always
have the whole thing together including the entire anode compartment before
doing the cathode network.
Using this method, I can usually turn on the amp and not see the SWR meter
on the exciter even wiggle at full power out. While other methods may have
some theoretical advantage, they have no practical merit in my
not-so-humble-opinion.
I hope someone gets a little use out of this, it took me a long time to
type it all in with two fingers.
73,
Larry - W7IUV
w7iuv@axtek.com
http://www.axtek.com/w7iuv
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