• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Positive side of sine wave seems elongated

Since you only have 8 Ohm output taps on each amplifier, then . . .

Get Two 8 Ohm resistors.
Two 8 Ohm resistors in parallel = 4 Ohms
Two 8 Ohm resistors in series = 16 Ohms

Try 5.6Vrms with 8 Ohm load, '3.5k', then '5k' amplifier.
Then change the load on each amplifier to 4 Ohms, then to 16 Ohms.

Next, 8Vrms with 8 Ohm load, '3.5k', then '5k" amplifier.
Then change the load on each amplifier to 4 Ohms, then to 16 Ohms.

You will see the change of the sine wave shape at the output.

Many "8" Ohm loudspeakers impedance will vary from 4 Ohms to 16 Ohms, depending on the frequency.
 
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