> I did not think, or say, it was I don't know why you brought Orwell
> into it.. You asked if I had read it- I said yes. If you insist on
> asking silly questions, at least take the answer at face value. > >//
> 3-500Z manufacturers say 400mA. In my experiences, a fresh 3-500Z
> >begins to saturate c. 420mA. However, one amplifier "expert"says
> tuning >up at 550mA is fb and he claims to have a letter from Eimac
> saying such. > He has not produced the letter. >My guess is that
> this letter is unsliced bologna.
>
> Like the references (quotes) I have asked you about a couple of times
> recently?
Anyone who claims a 3-500Z starts to "saturate" at "c. 420 mA"
clearly has no idea what he is saying, or is intentionally giving
misinformation.
Thoriated tungsten tubes typically begin to show emission limits at
50-100 mA per watt at 1900 degrees C, which places a 15 ampere
5 volt filament at 3.75-7.5 amperes for the beginning point of
emission limiting. (source Vacuum Tube Electron Emission,
Electronic Designers Handbook 2nd edition section 9-9).
The actual fully saturated emission of 3-500Z, where no more
current can be draw no matter what the applied voltages are, is in
the order of 11 amperes.
You can easily understand the "game" when you read step 13 of
the AL80A manual which is either ignored or misquoted. Step 13
says "In CW operation drive power is reduced until plate current is
400mA or less."
1.) On one hand, claims are made by a certain person a parasitic
can cause enough anode current to "bend filament wires from
magnetic fields".
2.) On the other hand, the same person claims he "starts to see
current saturation at 420 mA".
GOOD tuning instructions tell a person to over-couple the PA
(which reduces gain, reduces peak tank voltages, and improves
linearity).
POOR tuning instructions tell a person to load the PA only to the
expected maximum average current, which virtually ensures
excessive tank voltages and non-linearity on peaks.
73, Tom W8JI
W8JI@contesting.com
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