I built a Class D push-pull CW HF TX with 74HC240s providing
oscillation, buffering, an extra inverter on one side, and two stages
of current amplification, eventually driving a pair of IRF530
MOSFETs..

It looks like I struck a good balance even if there was a phase
offset.

This is what happened.

I turned ann inversting 8-section driver 74HC240 from a single-ended
oscillator-buffer-4Xamp (N7KSB style), into this push-pull monster:

| -inverter-2Xamp-16Xamp-...
VXO-buffer-buffer-|
|-------------2Xamp-16Xamp-...

From VXO to the 2+2 sections in push-pull current amplifier, all fits
into one 74HC240, fed at 5Vdc. Then, in a 8X equivalent fanout, I put
2 x 74HC240 on each side, fed at 8Vdc. 16 sections of current
amplification per side provide A LOT of current, already delivered
over 1W RF, and proved more than sufficient for driving a pair of
IRF530's in push pull with individually trimmed positive DC bias,
probably with room for further expansion.

The interesting fact is that there is one extra inverting section on
one side only. On that side the signal should have been delayed by
20-30ns, the propagation time for one section. At 10MHz this should
equal 70-110 degrees. In theory this should mean that both push-pull
sides should spend 110 degrees in high status (MOSFETs conducting),
and 110 degrees not conducting, leaving only 140 degrees for honest-to-
G_d pushpullery. :-(

Woe betide such a push-pull... BUT... with my scope having one
channel KO, I can't juxtapose the events - I can only combine the
results in the output transformer.

The result seems like a pretty symmetric waveform, with steep voltage
peaks on both sides (output balun primary still not tuned). Once
filtered into a sinusoid, I see about 60W DC going in and about 45-50W
RF coming out, with negligible second harmonic.

Is this normal? What did I get wrong? (I.e. got right, but just by
chance). Would I be wasting my time if I sought more push-pull symmety
by means of an unbal transformer? I mean somethign like this:

|-buffer-2Xamp-...
VXO-buffer-unbal
|-buffer-2Xamp-...

Any wisdom welcome!

[OK, I am going to have the scope's 2nd channel fixed anyway... :-) ]