>
>measures wrote:
>>
>> >Rich says:
>> >
>> >>The basic problem is that there was no way to keep the screen bypass
>> >>capacitor adequately charged during voice modulation
>> >
>> >I don't understand. It appears to me that when there is a signal, there are
>> >screen volts.
>>
>> Not until the screen bypass C becomes sufficiently charged. Another
>> problem is keeping the screen bypass C from mostly discharging on soft
>> syllables. The semi-obvious solution is to Not Allow the screen bypass C
>> to discharge as long as the amplifier is in operation. This is where
>> Thornley seemingly derailed
>>
>> > If it's a big signal, there's lots of screen volts, which you
>> >need because you wants lots of plate current. If it's a small signal, the
>> >peak plate current is less, so you don't need as many screen volts.
>>
>> In order to achieve linear amplification, current gain must be constant
>> at All signal levels. Screen potential has a large effect on current
>> gain. At 33% of normal screen volts, an 8171 exhibits 1/4 of normal
>> current gain.
>>
>> > So it
>> >appears that screen time constant should be short enough to follow the
>> >envelope of the signal - which in the original, it was.
>> >
>> The result will undoubtedly be varying gain.
>
>
>Seems to me that this beast will do just fine on 100% duty cycle modes:
>AM, FM and SSB-SSTV, SSB-RTTY, SSB-PSK, but query it's CW and speech-SSB
>performance?
CW would likely be ok.
>What was it originally meant to do?
SSB-voice plus all the rest. // At the time when Thornley wrote the
article, the 6AS7/6080, and 6336 low-Mu triodes were being produced.
Such tubes were quite useful for building regulated screen-supplies
because they could operate at full-throttle entirely in Class AB1 -
meaning that maximum current could be obtained with 0w of DC grid drive.
. Perhaps Thornley was simply not well-read on what a designer could do
with such devices?.
>
cheers, Ian
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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