Quote:
Originally Posted by wa2ise
The cost cutting went too far there. That arrangement won't sound that good. I'd install a real phase inverter tube somewhere, probably under the chassis.
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Short of adding a real phase inverter, another way to get p-p output on the cheap is to use a grounded-grid, common cathode setup.
That's where both tubes' cathodes are strapped together and
unbypassed.
Tube 1 is driven in the totally conventional manner (ie., thru a coupling cap from the first AF stage).
Tube 2 has its control grid (G1) grounded. Since Tube 2 shares common cathode with Tube 1, it is driven 180 degrees out of phase via its grounded grid. Ergo, push-pull.
The cathode resistor's value is chosen to bias the tubes' current at (roughly) the most linear spot on the curve.
This method has a few downsides, but offers real push-pull with minimal parts.