[AMPS] 3-500Z emission saturation

[Steve Katz]

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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