15-07-2022, 07:11 AM
(This post was last modified: 15-07-2022, 07:12 AM by Murphyv310.)
Hi.
In addition. We actually don't want the voltage between grid 1 and cathode to be "too" negative as this will eventually turn the valve off and when you feed in an audio signal only the positive half cycles of the waveform will be amplified, resulting in severe distortion. Class A amplifiers need sufficient bias so it won't clip with the full expected drive signal. There is also a bit of headroom added to the bias.
Cathode resistors often drop in value as they age unlike high values that go higher, its a good idea to replace the cathode resistor if its dropped even by a few percent as its enough to increase cathode current, shortening the valve life.
In addition. We actually don't want the voltage between grid 1 and cathode to be "too" negative as this will eventually turn the valve off and when you feed in an audio signal only the positive half cycles of the waveform will be amplified, resulting in severe distortion. Class A amplifiers need sufficient bias so it won't clip with the full expected drive signal. There is also a bit of headroom added to the bias.
Cathode resistors often drop in value as they age unlike high values that go higher, its a good idea to replace the cathode resistor if its dropped even by a few percent as its enough to increase cathode current, shortening the valve life.
