[sdiy] Tube amp problem

[eric b]

>>But class A is
>>always horribly inefficient. less than 16%? 
>The theoretical maximum efficiency is 50% I think.

50% is maximum efficiency, and assumes the load impedance
is a perfect match to the tube resistance. This gives
high distortion, and is only seen in RF power amplifiers
or specialized applications.
Include the heater consumption, and it is more like 40%.

This audio circuit does NOT load the tube for optimal
efficiency--audio power amps always load the tube
with about 2-3 times the plate resistance, to assure
lowest distortion (it is a compromise between linearity and
efficiency). Under such conditions, efficiency
of a single-ended class A circuit is about 16-25%.

>With parafeed the guys won't meet their goal of producing at least 15 Watts. 
>If I'd change something I'd go push pull. With a pair of EL34 one 
>can make up to 100W, but that would mean a diffrent output transformer.

Their circuit will come close to 15W. Just a few
issues--mostly with tube quality, not their circuit...
I do not think parafeed will not improve efficiency--
only distortion, by preventing output transformer
saturation.





E. Barbour
metasonix