Reg,

A truly wonderful example. If you don't mind, I would like to add to this.
See below.

"Reg Edwards" wrote in message
...
"Tarmo Tammaru" wrote
"Reg Edwards" wrote
Tam,

The only problem is that caused by entirely unnecessary
complications introduced by people being too clever.

First design a single-ended, class-A, audio amplifier
like a 6V6 beam-tetrode tube plus a transformer to
drive an 8-ohm speaker.

Then calculate the source resistance seen from the
speaker looking back into the amplifier.

To save time searching for manufacturers data, assume:

DC plate supply is 250 volts.
Peak signal at plate 200 volts.
Internal plate resistance, from mnfr's curves, is 100
K-ohms.
Audio power output = 5watts into 8-ohms load.
Peak volts across load = 8.944 volts peak.
Transformer turns ratio = 22.36

Now, let's see what would happen if Reg had tried to "conjugate Match" the
speaker to the 6V6.

Given that the plate resistance is 100K, and desired Po is 5 W, The voltage
required to generate 5W across 100K can easily be shown to be

VDC = 50 + SQRT (5 x 2 x 100000) = 50 + 1000 = 1050V

This is about 3 times the rated maximum plate voltage.

The efficiency of an amplifier, based on using the Norton equivalence, is
reduced by the amount

(1 + Rs/Rl) = 1 + 100K/100K = 2

Note that in Reg'd design the load impedance was

8 x 22.36 x22.36 = 4000 Ohms, and his efficiency was reduced by only

1 + 4000/100000 = 1.04

So, by matching, the efficiency has neen reduced by 2/1.04 =1.923.

Anybody for going down to the local power company and conjugate matching all
thouse pesky AC generators?

Tam/WB2TT