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Old 11th May 2008, 07:05 PM   #1
neazoi is offline neazoi  Greece
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Default Pure class-A or class AB?

Dear all,
As I am not an electronic engineer, I need to know if the next circuit
http://www.ptsoundlab.com/tubes/otl/.../6as7gtaga.htm
operates in true class A or class AB.
Thank you all
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Old 11th May 2008, 11:05 PM   #2
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hey-Hey!!!,
If the set of four 6AS7 triodes can avoid cut-off before reaching rated power it will be Class A. For 25W, the delivered current into the load is 1.76Amps. That is a bit more than 400 mA idle per triode section. At 150V that equates to 60W give or take a bit heat per triode plate. Check the data sheet and see if they'll stand 60W per plate and your answer should be obvious, yes?
cheers,
Douglas
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Old 12th May 2008, 07:56 AM   #3
neazoi is offline neazoi  Greece
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Dear sir,
I found the datasheet here: http://www.mif.pg.gda.pl/homepages/f...49/6/6AS7G.pdf

I would greatly appreciate if you could help me on that.
Best regards from the sunny and windy Greece
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Old 12th May 2008, 08:40 AM   #4
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I would guess AB. 4 of them in parallel can do 52 watts(13 watts per plate). They can idle at only 85mA per section at 150V to stay within plate dissipation limits. Total idle current is only 340mA. The datasheet says that using fixed bias isnt recommended but thats how its built.
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Old 12th May 2008, 08:49 AM   #5
neazoi is offline neazoi  Greece
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Thank you very much
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Old 12th May 2008, 08:51 AM   #6
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Woops you read while I was having a second look and editing my first post. But still definitely AB.
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