>Thank you, you guys for your comments. However, I am absolutely sure about
>this. It is quite late right now so I can not dig into my amplifier library.
>Even so I refer to W1JR:s article in HAM RADIO February 1985 page 38. And if
>my memory not fails, I have seen it in one of my EIMAC papers
? Which one? The latest version of the 8877 specs sheets mentions
nothing about heater inrush.
>and discussed
>the problem with the EIMAC people during my visit in the factory. And I know
>of at least 2 guys who had filaments breaking down in their ALPHA amplifers.
> Maybe this amplifier has a overrated filament transformer and no current
>limiting due low ohmic transformer windings.
>
? If an 8877 amplifier has no glitch protection diode in the neg. HV
circuitry, the cathode circuit will spike to several negative kV whenever
a positive. HV arc takes place. When such a cathode spike takes place,
if one side of the heater is grounded, the cathode will arc to the heater
and the heater can burn out. . . The bottom-line is that the safest
way to operate an 8877 is with the cathode tied to one side of the
heater, neither side of the heater grounded, and a 1A approx. 20uH
bifilar RF choke between the heater and the heater transformer secondary.
// Would you like to take a wild and crazy guess whether or not the
Alpha 77 grounds one side of the 8877's heater?
- cheers, Hans
>----------
>>Från: measures <measures@vcnet.com>
>>Till: "Hans Goldschmidt" <sm5ki@algonet.se>, "Jack Brabham"
><w4asm@mindspring.com>, "AMPS" <amps@contesting.com>
>>Ämne: Re: SV: [AMPS] PA-77 question
>>Datum: mån 13 sep 1999 21.08
>>
>
>>
>>>Hello!
>>>Watch out for that filament inrush current. HAS DESTROYED MANY A 8877. You
>>>limit it with a resistor in series with the primary of the filament
>>>transformer and short it out after some seconds.
>>
>>? Although Eimac does provide a warning about limiting inrush current to
>>some filament-type tubes like the 3-500Z, Eimac gives no warning about
>>limiting current to heater-type tubes such as the 8877.
>>
>>
>>- Rich..., 805.386.3734, www.vcnet.com/measures.
>>
>>
>>--
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>>
>>
- Rich..., 805.386.3734, www.vcnet.com/measures.
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