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Bias Regulation

"...the Tent Labs Bias Supply ... can source or sink 1.5mA."

According to the simulation, source current is very small, less than 100 uA. However, sink current might be more problematic. I added a simple shunt regulator to get an idea of what's required. In the circuit below, if the grid is driven hard, Q2 must sink 3-4 mA in order to maintain a constant DC voltage level at the bypass capacitor.

This doesn't mean the Tent supply won't work, but its effectiveness will depend on how hard the 845 is driven. It appears that if you input a sine wave at full A2 power, bias voltage will increase if the sink is limited to 1.5mA. However, if the amplifier only experiences brief A2 operation on transient peaks, the 1.5 mA sink should be satisfactory. Also, the larger the value of the bypass cap (or reservoir cap, as Naz referred to it), the longer it takes to charge up when grid current is drawn. That provides a larger window over which grid current can be drawn without significantly disturbing the amplifier's operating conditions.

I could try to simulate this with a 845 if you're interested. However, I've found that many tube models don't draw grid current properly. The 211 I'm using now was the third one I tried.










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  • Bias Regulation - Triode_Kingdom 08:44:20 09/08/14 (3)

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