[ARC5] Way OT -- SX-28

[Tom Lee]

You are absolutely right, Jim. Class-A is the least efficient of the standard topologies. Class-B was invented precisely because of its greater efficiency. Your analysis is spot on: A Class-A amp is always burning power, and is fated to deliver less than 50% efficiency. Class-B amps are theoretically capable of 70+% peak efficiency.

—Cheers,
Tom

Sent from my iThing, so please forgive typos and brevity.

> On Aug 6, 2021, at 1:28 PM, Jim Haynes <jhhaynes at earthlink.net> wrote:
> 
> On Fri, 6 Aug 2021, Rich Post wrote:
> 
>> AFAIK, the move was less for cost-cutting but more for power consumption. 
>> The FCC used a lot of these in portable application, run off vibrator
>> packs.  A single-ended audio would significantly reduced B+ current demand.
> One could argue with that.  Loy Barton, who developed the idea of
> amplitude modulating an RF amplifier using a Class B audio amplifier,
> once advocated the use of a two-tube push-pull audio output stage in
> battery operated radio receivers.  The reasoning was that a Class A
> audio amplifier is pulling current all the time whereas a Class B
> push-pull amplifier pulls current only when there is some audio present
> to amplify.  So the Class B audio would give longer battery life.
> (At least for the B-battery - more current would be needed from the
> A-battery to power the filaments of the two tubes.)______________________________________________________________
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