From a quick look around, running Class A single ended mode with a Va of 250: N78 likes 7K and KT61 likes 6K.

Most Australian radios using 6V6GT/6AQ5's generally have 5K on the primary of the O/P transformers. But this appears not to be a hard and fast rule. I have seen 7K transformers used with 6V6GT/6AQ5's and this has been part of the original circuit.

The amended 429MA with the 6AQ5 has a note saying "Socket voltages are the same as for original 429MA using N78". This would mean the 429MA KT61/N78/6AQ5 all run 190v on the plate (Anode?)

I've measured the OP transformer on my KT61 chassis with the means available to me and came up with the following figures;

Primary - 13.81v
Secondary - 0.288v
Speaker DC resistance - 2.8 ohms

I took the liberty of rounding off a few numbers in my calculations (mainly 'cause I can't figure out how to use a memory key on my phone calculator) and came up with an impedance of 6438 ohms, right in the middle of what the KT61/N78 like - 6000 and 7000 ohms.

I've read that the figure that should be used for the speaker in these calculations is the impedance, not the DC resistance. This can supposedly be roughly calculated by multiplying the DC resistance by 1.25. Is this correct? If so it makes the speaker 3.5 ohms and total impedance a tad over 8000 ohms.

All very strange to me but if I did convert this KT61 chassis to a 6V6GT in the future, is the 6V6 going to be happy with this?

I checked another couple of AWA's that run 6V6's, my 500M - plate volotage 235v and 516M - plate voltage 200v. Both of these as well as both variations of the 429MA seem to run the same XA2 OP transformer. Did AWA match the output impedance by varying the speaker impedance or just didn't really care too much about getting it right or are output valves very tolerant?

I did find a 1944 AWV data sheet for the 6v6gt which showed that apart from the plate voltage, the screen voltage has an enourmous effect on the load resistance. This figure is left out on later sheets but might explain the differences. This stuff starts going beyond my limited knowledge though.