At 10:13 AM 12/11/97 -0800, Rich Measures wrote:
>>The paper is unsigned. I got it along with a stack of Eimac Service
>>Bulletins.
>>I got them from Reid Brandon.
>
>Interesting. This is the fellow who seemed to be unaware of the QST
>articles on parasitics. (pages 72 -75 of 9/94 QST}
>- After I telephoned Eimac and was told that a certain ex-employee was
>never an "R+D Engineering Manager" -- as Mr. Rauch had claimed, I decided
>it might be a good idea check out another of Mr. Rauch's Eimac-pals. I
>telephoned Eimac's CA facility and was told that Mr. Brandon was not
>employed in Eimac's Engineering Department.
Mr. Brandon's title on his letter to me of 9/26/95 listed him as
"applications engineer".
>
>> "You might ask him who wrote the paper. It did
>>state that the voltage involved in the glitch through a tube is 50 volts.
>
>This seems reasonable. However, the vanishing gas theorum doesn't.\
Eimac does not mention gas as a player in an internal arc in a tube.
They define an arc as "a self-sustained discharge of electricity, between
electrodes in a vacuum environment, which has a voltage drop at the
cathode of the order of the minimum ionizing potential of the environment.
The arc supports large currents by providing its own mechanism of electron
emission from the negative terminal plus space charge neutralization."
Sounds like the "Rocky Point" phenomenon to me.
Perhaps someone has a copy of the book "Vacuum Arcs-Theory and Application"
by J.M. Lafferty, John Wiley and Sons, New York ISBN 0-470-06506-4. This
might be interesting reading on the subject.
>>>>The grid of an 8877 is rated at 25W dissipation. The grid of a 3-500Z is
>>>>rated at 20W dissipation. The "in excess of four Joules will permanently
>>>>damage" statement seems to be questionable. .
>>>>[note: a Joule (J) is 1 watt for 1 second}
>>>>- For a tube whose grid is rated at 1W, 4J might possibly cause damage.
>>>>For a tube whose grid is rated at 25W, how could 4J damage the grid? I
>>>>find it hard to believe that a legitimate power grid tube engineer wrote
>>>>such a statement, Phil. Do you know the name of the person who wrote it?
Grid dissipation ratings have nothing to do with how much abuse the small
grid wires can withstand when an arc occurs. Tom had a good explanation
a while back on what makes up the complex waveform on the grid during normal
operation. In an arc, there is no waveform...it is strait DC; electrons being
emitted from the negative terminal, plus space charge neutralization. (quoting
Eimac again) IMO, 50 volts at 5 Joules (DC) has to have many times more
distructive power than 25 watts of HF RF.
>>That means that in a 4000 volt supply, the glitch resistor will have 3950
>>volts accross it.
>True enough, Phil, however, there could easily be hundreds of volts total
>drop across the ohms in HV-RFC and the ESR of the filter capacitors --
>assuming that the alleged anode/grid arc actually took place.
The components in the RF deck are not players in the design of a proper
glitch resistor. The "Eimac Test" involves only the power supply section;
which takes into account the ESR of the filter caps. and the follow-on
energy provided by the a.c. mains before the contactor opens. The glitch
resistor is to be just enough ohms to keep the #40 wire from melting, and
enough wattage to keep it from distructing while the contactor does it's
thing. The drop across the plate RFC and the effect of other components
are an added bonus in this case, but the glitch resistor protects the
choke and EVERYTHING else in the RF deck.
>Thanks, however, If the paper is unsigned, receiving a copy of it would
>not reveal the author. OTOH, Mr. Brandon quite probably reads the [AMPS]
>mailing-list, so perhaps he can enlighten us.
He may read it, but I wish he would share his expertise with us as a
contributor. I meant that if you call him, he might tell you his title
and who did the paper. BTW...none of the Eimac Service Bulletins are signed,
as is the norm in both the electronic and aviation industry.
(((73)))
Phil, K5PC
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