Richard Hosking wrote:

As I understand it the output impedance approximates to Vcc*Vcc/Po, where Po
is output power and Vcc is the supply voltage
It looks like your measurements point to 50 ohms as about right. How were
you measuring the voltage? - this might affect the measurement


Vcc * Vcc / Po = 13.8 * 13.8 / .352 = 540 ohms (for a 47 ohm load).

This value is certainly in the right ballpark.

I guess that I should also measure the current taken by the final stage and
see if this ties in too.

I connected various 1/4w resistors across the output using a couple of
adaptors, but being aware to keep wire lengths as short as possible. I then
simply used a scope probe and scope to make the measurement. Scope probe was a
standard x10 10Mohm impedance and presumably small C.

Interestingly I was surprised at the magnitude of the voltages for such a tiny
power.

regards..

--Gary