30 watt class A chopper controlled bias with 6 EL84 - diyAudio
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Old 11th May 2015, 04:31 PM   #1
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Default 30 watt class A chopper controlled bias with 6 EL84

this is the design i worked on for a while .it is ready to launch for comments.
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Old 11th May 2015, 06:57 PM   #2
DF96 is offline DF96  England
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To save us all from the effort of reverse-engineering a circuit which might contain mistakes, why not help us by describing that it is supposed to do? Then things like potentially reverse-biased diodes might make sense.
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Old 11th May 2015, 07:30 PM   #3
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i can asurre you there are no mistakes in the schematic.you can go to my facebook to see the amp working.the bias circuit works as followed:the voltage drop acros the resistor 5.6 ohm is chopped into aprox squarewave t
hen amplified bij the triode and negative rectified. facebook page :vanlandschoot dries
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Old 11th May 2015, 07:54 PM   #4
DF96 is offline DF96  England
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So you are relying on leakage current through the reverse-biased 1N4007 diodes to feed the signal from the resistor?
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Old 11th May 2015, 07:54 PM   #5
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at frist glance one may think there are mistakes but to sombody with the technical skils and understanding electronics wil be able to decipher the schema.d ont underestimate this amp every resitor diode or cap has his purpose.
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Old 11th May 2015, 08:00 PM   #6
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no the diode on the grid holds the grid of the triode on aprox - 0.5 volt in the negative swing of the sinewave derived via 100k resistor.in the positive swing diode starts conducting aprox 0.5 volt above the voltage over theresitor(5.6 ohm)
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Old 11th May 2015, 08:30 PM   #7
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scope image of the signal at the grid of the triode scope :0,5v/div center =0 volt
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Last edited by vanlandschoot; 11th May 2015 at 08:39 PM.
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Old 11th May 2015, 08:37 PM   #8
TheGimp is offline TheGimp  United States
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Square wave drive to the ECF80, whose output is capacitively coupled to the zener diode clamp, and then coupled through the diode to the 10uF filter cap to form the bias voltage.

Chopper generated bias supply. Avoids needing a winding for bias voltage.
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Old 11th May 2015, 08:46 PM   #9
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nobody ever thought to do it this way !! when i was thinking of this amp i had some ecf80 tubes form my dad and as the design went on i got 1 triode spare so one night i got up and made this schema .to my suprise it worked like a clock.
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Old 11th May 2015, 08:50 PM   #10
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the zener diode does not clamp exept when the amp is overdriven.there is more to this schematic!!
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