5E3 X-Y display of output

[J M Fahey]

I think whatever voltage or waveform you get on the *secondary* will affect the speaker movement.
After all, a speaker is a motor (literally) driving a mechanical load (cone/coil/etc. plus the air mass load).
Now, if you have spikes on the primary, *across the parasite inductance* , which get clamped there but not transmitted to the secondary, the voice coil does not know they exist.
Transformers couple primary and secondary *very* well, they are one of the most eficient machines Man invented, but not 100%.

[loudthud]

These pics are from a re-issue 5F6A, one of those that came out in the 90s. It has a GZ34 rectifier. The setup is a little different. Because the speakers connect through four phono jacks, it was easier to unsolder the ground line of the output transformer and insert the current sense resistor there. I found a 0.05 ohm resistor and verified the resistance. The vertical signal to the scope was inverted so it would display the same as the previous shots. So, the vertical deflection factor is 200mV/0.05 ohms = 4 amps per division. The horizontal deflection is 5V per division. Just for reference, 50W at 2 ohms is 14.14V peak, 7.07A peak.

[trobbins]

Neat. I think the 'outer bars' are a good representation of the output valve saturation regions being represented. When I look at your original post, the image with the resistor load doesn't show that charactaristic - which is because the speaker inductance allows the primary dynamic impedance to be shown, rather than the secondary impedance being clamped to just a resistance (and hence V&I can only move on the R line). To see an uncluttered primary side valve saturation characteristic would require a secondary resistive load with primary side voltage and current sensing (which is then not so easy).