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03-03-2021, 08:24 PM
Hi liquidair
It is normal to see the changes in the electron flow within the tube as you describe. If you see the plates turn orange then things are not quite right - possible bias failure, so turn off the power immediately.
We assume yor amp has typical voltage ratios?
In normal operation of 99% of tetrode / pentode push-pull output stages, Va is higher than Vs at idle. During the signal cycle, each plate voltage swings much lower than Vs getting withing a few tens of volts of ground. You will see a sine wave output for a sine wave input. If idle Va is made far lower than idle Vs, the input sine wave will distort into a triange and screen dissipation will be excessive.
Have fun
It is normal to see the changes in the electron flow within the tube as you describe. If you see the plates turn orange then things are not quite right - possible bias failure, so turn off the power immediately.
We assume yor amp has typical voltage ratios?
In normal operation of 99% of tetrode / pentode push-pull output stages, Va is higher than Vs at idle. During the signal cycle, each plate voltage swings much lower than Vs getting withing a few tens of volts of ground. You will see a sine wave output for a sine wave input. If idle Va is made far lower than idle Vs, the input sine wave will distort into a triange and screen dissipation will be excessive.
Have fun
