Any port in a storm.
On Jul 21, 2006, at 4:03 AM, Tom W8JI wrote:
>
>>>> If the tube is not gassy, and the grid is floating, the
>>>> electron
>>>> stream from the cathode probably raises the grid-cathode
>>>> (fil-CT)
>>>> potential to a few volts negative
>>
>> So if it doesn't matter, why do tube manufacturers specify
>> a maximum grid - cathode resistance for a lot of tubes?
>> Even low power audio tubes used in Class A?
>> My experience is that exceeding the the maximum
>> grid-cathode resistance can (but not always does) lead to
>> a plate current runaway, even in tubes with no measurable
>> gas (as measured by grid current)
>
> That's the same experience anyone who has built audio amps
> and played with grid resistors runs into.
>
> I had a pair of 6146's in a bass guitar amp and in an effort
> to get better bass used very high grid resistors, and had
> runaway in the 6146's when they got hot. Grids went
> positive. Either every new 6146 RCA I bought that year was
> bad, or I had too much grid leak for hot tube temps.
>
> 73 Tom
>
>
>
>
>
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R L MEASURES, AG6K. 805-386-3734
r@somis.org
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