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This Post Has Been Edited by the Author
In Reply to: RE: PP Class A OPT Loading posted by PakProtector on March 18, 2012 at 12:21:37
When I first studied the treatment of push-pull tubes in the standard texts, including the Radiotron book, I found the following to be easier to understand. (Ignoring inductance and other reactive considerations for simplicity.)
1. Treat the transformer as three equal windings, with B+ applied to the connection between two windings to make the center-tapped primary.
2. Put a largish load resistor on the third winding.
3. If you measure only the transformer, the "plate-to-plate" impedance, which is that specified by the transformer vendor, equals 4x the load resistor on the third winding, since there is a 2:1 turns ratio.
4. In actual practice, the total amp-turns in all three windings, carefully added together, equals zero at all times, if the quiescent condition has zero total amp-turns (equivalent to having equal quiescent currents in the two tubes).
From these axioms, you can see how the currents in the two plates affect the voltages on the same plate and the other plate, and find the voltage into the (fictional) load resistor. To make it less fictional, you can replace the load resistor by a step-down transformer from that resistance (1/4 of the so-called plate-to-plate impedance for the circuit) to 8 ohms or whatever.
5.
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