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Re: Ultrasonic AC for DHT Filament

dave wrote:

"looking at batteries, we have the perfect isolation from the AC source, but we do not have the benefits of the single current path for AC since the battery behaves as a cap across the filament... and batteries like caps are nonlinear, and i just don't find it to be a good practice to put 1/2 of your signal current through a nonlinear device, either put all of it through it or none of it."

Here is another case where wiring the filament with a virtual center tap can help. In my amps, I have an automatic arrangment that hot switchs the batterys every half hour. This way I get by with small batteries and can run the amps indefinitely. This required the filament circuit to be setup as if there were AC heating otherwise there is a pop when the batteries switch.

The advantage to the AC wiring scheme is both ends of the filament are connected to the cathode resistor with equal value resistors. AC analysis would make me think that there is no signal current through the batteries with this arrangement.

Gary



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