On Jul 21, 2006, at 12:44 AM, Ian White GM3SEK wrote:
> Yesterday ended with two almost identical exchanges in different
> threads
> of the debate. I am pulling both back together here.
>
>
> R L Measures wrote:
>>>> On Jul 20, 2006, at 4:42 AM, Harold Mandel wrote:
>>>>
>>>>> The GM3SEK and WD7S Triode and Tetrode Controller boards,
>>>>> when suitably integrated, when properly adjusted, serve to
>>>>> protect tubes and power supplies in a much faster time frame
>>>>> than fuses.
>>>>
>>>> Hal --- Does the GM3SEK / WD7S Triode Controller board for an 8877
>>>> use a grid protect transistor rated at >50A?
>
> I had replied:
>>>
>>> Despite requests in the past, you have never provided a specific
>>> example
>>> of a circuit that needs a "grid protect transistor rated at >50A".
>>
>> An example is any amplifier that uses an 8877.
>>
>
> The question is about the control circuit, not the type of tube.
> PLEASE
> name a specific amplifier that has schematic we can all look at,
> showing
> a "grid protect transistor" in the configuration you're talking about.
So far, I found one model Alpha that uses a transistor amplifier to
drive a relay that interrupts the flow of grid-I, however, I remember
helping a friend repair an Alpha that has a shorted transistor in the
grid-protect circuit and one gold-sputtered 8874. .
>
>
>>>
>>> The schematic of my grid-protection circuit is in the Triode Board
>>> user
>>> manual which is downloadable from the website. The only
>>> transistor in
>>> this circuit is a 2N2222 that senses a small fraction of the grid
>>> current, and can handle even extreme fault conditions.
>>
>> Does the 2N2222 interrupt the flow of grid current if the limit is
>> exceeded?
>
> Have you looked at the schematic yet?
No. What is the URL of the schematic?
> If you have, you can see that the
> answer is "No, the 2N2222 is not located in the direct path of the
> grid
> current".
>
So how does this circuit stop 50A of grid current?
>
> In a parallel thread of the debate, Rich had also replied:
>> On Jul 20, 2006, at 3:40 PM, Ian White GM3SEK wrote:
>>> I don't know of any electronic protection circuit that actually
>>> works
>>> that way. Despite requests in the past, Rich has never shown an
>>> example
>>> of what he claims.
>>
>> An 8877 cathode can emit 50A. If 50A is flowing into the grid, how
>> does your electronic circuitry stop it?...
>
> I already posted the shorter version yesterday. The longer version
> (which is easier to understand because it includes diagrams) is in the
> downloadable user manual for the Triode Board. Here is a direct link:
> http://www.ifwtech.co.uk/g3sek/boards/triode/triode-manual.pdf
>
What is the URL of your schematic, Ian?
> My own circuit does not contain anything that could be correctly
> described as a "grid protect transistor" requiring a rating of >50A.
> Neither do I know of any other amplifier control circuit containing a
> transistor that fits that description.
>
> Unless Rich can provide a specific example of some other amplifier
> control circuit that does contain such a transistor, we may have to
> conclude that no such circuit actually exists.
As I recall, one model of Alpha 3, 8874 amps used a pass transistor
to interrupt the flow of dangerously high grid current
...
R L MEASURES, AG6K. 805-386-3734
r@somis.org
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