[Patrick Turner]

I am editing my website again to include better info, more info, and
better formatting. I think the two most visited pages have been the PP
and SE OPT calculation pages where ppl have wanted to know how to wind
themselves an OPT. The revised SE OPT calc page is about done
including many more diagrams and oscilloscope pics of distortion and
satutuation ppl should see whaile testing their amps.

The PP calc page is also going well, but I wanted to include a portion
about calculating anode dissipation, and I searched the web and all my
old books for a formula to allow for the calculation of total Pda at
any sine wave level while a substantial amount of Pda exists at idle.
I already have formulas to predict class B amp Pda, all very neat, but
useless for class AB where we may want to plot the graph of Pda from
max Vo of 0dB, then at -3dB, -6dB, -9dB, -12dB.

The formula for tube class B I derived from general theory with solid
state amps is:-

Total Pda, 2 tubes = Power input from power supply - audio power
output
= ( 0.9 x Ea x Va / BRLa ) - ( Va squared / BRLa )

Where Ea is the idle Ea Vdc between a and k, Va is the Vrms at one
anode of the PP pair, and BRLa is the class B load for one tube, ie,
RLa-a / 4.

The formula may be simplified to :-

Total Pda of the 2 tubes in class B at any level = Vaa x ( [ 1.8 x
Ea ] - Vaa ) / RLa-a.
( Vaa is anode to anode signal in Vrms ).

Obviously, Pda will be zero at Vaa = 0V. But with class AB amps Pda
might be 50W for two 6550 at idle.

With an existing amp, its easy to plot a graph for Pda, just measure
power input and power output, and Pda = Pin - Pout, for any level you
wish, but a formula should cover all operation, and even RDH4 is very
timid about providing one, like my other stack of old books.

Patrick Turner.