This is why some people spell it, "auspice," while others spell it "hoss
piss."
The only problem I find with the AL-80B, other than the borderline
workmanship (I had to solder the OPR/STBY switch myself, since the factory
was saving on solder at this location) is the incredibly wordy operating
instructions -- which warn not to exceed 400mA Ip but then go on to detail
ALC adjustments requiring 200mA Ig as a limit set. Really hard to get 200mA
Ig without exceeding 400mA Ip, unless the HV PS fails.
But, anyway...
WB2WIK/6
"Each success only buys an admission ticket to a more difficult problem." --
Henry Kissinger
> -----Original Message-----
> From: Tom Rauch [SMTP:w8ji@akorn.net]
> Sent: Tuesday, October 09, 2001 1:56 PM
> To: amps@contesting.com; Bill Aycock
> Subject: [AMPS] 3-500Z emission saturation
>
>
> > 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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