-----Original Message-----
From: measures <2@vc.net>
To: Peter Chadwick <Peter_Chadwick@mitel.com>; amps <amps@contesting.com>
To: <amps@contesting.com>
Date: 30 March 2000 20:10
Subject: RE: [AMPS] Is screen potential important?
>
>>
>>Rich says
>>
>>>Not until the screen bypass C becomes sufficiently charged
>>
>>But if this is 5 time constants, it's still far faster than the rise time
of
>>the envelope.
>
>My guess is that it takes more than this.
Why guess, it's elementary maths. Work out how close to final voltage you
get after 5 timeconstants.
>For an 8171 operating no lower
>than 3.5MHz, the screen/cathode capacitance is around 0.05uF. For
>1.8MHz, around .iuF. Also, the input signal is a voice. Since voice
>duty-cycle average around 15%, how are you going to charge the screen
>bypass cap to the needed 1500v with a15% source.
We've been through this. Something with that much screen C is not a good
candidate for a DAF type amp. Duty cycle isn't the issue - if the charging
system has a timeconstant much lower than the envelope risetime, the screen
voltage will follow it. That's all there is to it.
BTW, the original design ran with screen voltage up to 200V peak, compared
with 350V constant for 'regular' use, so you are probably not going to aim
for 1500V anyhow.
Steve
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