In Reply to: Re: Why doesn't anyone make a tube amp as follows? posted by Markw on April 30, 1999 at 05:31:09:
There are several manufacturers that advertise that their amps are push-pull AND class A. Ever hear of class A/AB? The amp is class A until it reaches a certain power output at which the amp turns into class AB. I have no idea how this type of biasing is arranged (one tube has a higher DC bias than the other?). I think that some manufacturers are biasing their amps class A/AB and advertising them as class A only. Slightly truthful advertising.My now unused sony receiver has a PP output stage but in the spec sheet it is listed as class A out to 15-20 watts. At that point it switches to class AB to 100 watts. It's highly probable that there are tube PP designs arranged in such a fashion. After all, both devices (tube & SS) are operating on the same principal: switches that have variable conductance/resistance which is controlled by an incoming signal on the grid/gate/base.
Have fun,
Tom S.
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