[Amps] grid fuses

[R L Measures]

On Jul 22, 2006, at 9:17 AM, Tom W8JI wrote:

>> "...If it's open, the most it might do would be to attract
>> a few
>> electrons being negative like was mentioned...(etc.)"
>>
>> In the old days this was called 'contact bias,' and was
>> the principle
>> incorporated intentionally in a grid-leak biased stage.
>
> People like to misapply what happens in a 12AX7 dual triode
> and other thumb-sized tubes operating at 50-300 volts P-G
> voltage to fist-sized tubes running at 3kv and more.
>
> Contact bias generally does not work in large HV tubes and
> should never even remotely be considered a reliable bias
> method.

Mr. Rauch -- No one said that contact bias is suitable for actual  
bias. IMO, electron contact effect will negatively bias a floating  
grid in a 12AX7 the same way it does a 3-500Z grid. At this point in  
this hair-pull, we need a third party to float a 3-500Z grid and tell  
us what resulted.

> It's bad logic and even worse engineering to
> consider contact bias reliable in power grid tubes.

Nobody here proposed this, Tom.

> They
> don't even recommend it in 6AQ5's, let alone something 200
> times larger with ten times the HV (or more).
>
> 73 Tom
>

R L MEASURES, AG6K. 805-386-3734
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