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Old 26th August 2012, 01:40 PM   #1141
Antoinel is offline Antoinel  United States
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Originally Posted by lhquam View Post
I am not sure what the relevance is for "AC ground". What is important are the bias voltages relative to the bottom of the FET source resistors. We are trying to maintain these voltages at constant levels under varying signal conditions.
The AC drive signal to the upper JFET will be relatively larger in magnitude than for the lower JFET. In your opinion is it or not?

Last edited by Antoinel; 26th August 2012 at 01:45 PM.
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Old 26th August 2012, 01:50 PM   #1142
buzzforb is offline buzzforb  United States
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ZM, Why will it go bottatboom? Dont understand.It is used as Vref for so many bias circuts for transistors.
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Old 26th August 2012, 01:54 PM   #1143
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The AC drive signal to the upper JFET will be relatively larger in magnitude than for the lower JFET. In your opinion is it or not?
The AC drive signal is the same for both secondaries of the transformer (they don't know how they are being used). If you have a different resistance across one of the secondaries you may change the amplitude.
Please explain how could the AC drive signal be different in the secondaries?

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Old 26th August 2012, 02:04 PM   #1144
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ZM, Why will it go bottatboom? Dont understand.It is used as Vref for so many bias circuts for transistors.
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.....

you need to change places of leds and CCS
read what I wrote about 6k8 res on bobbo's sch
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Old 26th August 2012, 02:11 PM   #1145
buzzforb is offline buzzforb  United States
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Choice of Rs on output stage has affect on values of bias network. Is it in parallel with bias network?
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Old 26th August 2012, 02:15 PM   #1146
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no
, it isn't in parallel

it is important for for needed bias voltage span which you're having on trimpot

without Rs - say that you need 1V5 max

with Rs=0R47 and Iq=2A , you need 1V more
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Old 26th August 2012, 02:23 PM   #1147
buzzforb is offline buzzforb  United States
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Damn, i amignorant. If i use 2sk246, I can run at Idss, correct. Should i use1K resistor above to help with dissipation?
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Old 26th August 2012, 02:36 PM   #1148
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you can waste at least 50% of PSU voltage on additional resistor
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Old 26th August 2012, 02:54 PM   #1149
bobodioulasso is offline bobodioulasso  Europe
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now choose Rs value & Iq , and calculate that in.

ZM will allow at least 1mA through trimpot , and 3mA through zenner
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Old 26th August 2012, 02:55 PM   #1150
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go and build

say tnx! to Pa

if you can't find 3k trimpot - use 2K one , and 1K resistor below

and yes , you can use more than 10uF in series with secondary

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Last edited by Zen Mod; 26th August 2012 at 02:58 PM.
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