>
>
>On Thu, 26 Oct 2000 12:31:43 -0700 measures <2@vc.net> writes:
>>> If the DAF is built per the original design, with a time constant in
>>>the screen circuit that will allow the screen voltage to follow the
>>>envelope of the SSB signal, then a two-tone test will give valid
>>results.
>>>
>>What time constant? A two tone signal produces constant output in DAF
>>amplifiers, therefore the screen potential can not be following
>>anything.
>>
>
>Hi RIch,
>
> The effective screen resistance of the 4-125A is going to vary quite a
>bit in the DAF as the voltage is going to wander. Let's assume a typical
>value, for the moment, in the range of 10K-15K ohms plus there is an
>additional 27K, if I recall correctly, resistor to ground in some DAF
>implementations. Since there is a .005 uF capacitor in the DAF screen
>circuit, and neglecting the impedance of the charging circuit for the
>moment, the time constant of the screen "supply" is around 25-50 uS
>(considering the two screens plus maybe the resistor). This will be a
>little faster at higher drive levels and somewhat slower a lower drive
>levels
>
> In any case, it is quick enough to follow the envelope of a typical two
>tone test signal or voice generated SSB.
>
Screen potential does not wander during a 2-tone test.
end
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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