>
>> 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.
>
// 420mA was the average current measured. The corresponding peak
anode current would have been c. 1.25a.
>Thoriated tungsten tubes typically begin to show emission limits at
>50-100 mA per watt at 1900 degrees C,
// In Care and Feeding ..., Eimac states that the temp is c. 1820ºK.
,
>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).
>
// According to the 3-500Z constant current curves, peak currents above
1.2 amperes are progressively non-linear.
>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.
// Agreed, however, this has nothing to do with linear operation.
>
>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."
>
// Surely. The rub is that a tube that is tuned in its not-linear
region is hardly going to be linear when it not readjusted for operation
in the linear region.
>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".
>
// See photograph of bent 3-500Z filament helices on p.15 of "Parasitics
Revisited" in the September. 1990 *QST*.
>2.) On the other hand, the same person claims he "starts to see
>current saturation at 420 mA".
>
// This was in an SB-1000 with a low-hrs. tube. Mr. Rauch has not yet
published the alleged Eimac letter authorizing 500+mA for the 3-500Z.
>GOOD tuning instructions tell a person to over-couple the PA
>(which reduces gain, reduces peak tank voltages, and improves
>linearity).
>
// However, a well tuned up 3-500Z is already c. 8db cleaner than the
avg. transceiver, so no one is likely to notice a couple of db
improvement in amplifier IMD.
>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.
To: <amps@contesting.com>
// Date: 8 Nov 1996 05:45:01 GMT
...
(Tom Rauch):
>"And then I wrote the RF tank voltage can exceed the dc supply voltage by
> several times when the PA is unloaded. ,,,"
In a SB-220, Anode supply potential is c. 2900VDC. 3 x 2900V= 8700V.
Normal tank potential at the Tune-C is c. 2700V-pk. During a worst case
scenario, this potential is c. 3600V-pk. At sea-level, the Tune-C's
breakdown potential is c.3700v.
>73, Tom W8JI
>W8JI@contesting.com
>
cheers
- R. L. Measures, 805.386.3734, AG6K, www.vcnet.com/measures.
end
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