The SW-4A amp is not push pull, neither is the amp in the R-4A or R-4B. However, the SW-4 does have a push pull amp with two 6AQ5s and 1/2 of a 12AX7 as a phase inverter.
Most audio amps consist of two stages. The first is a voltage amp, usually a triode such as one unit of a 12AX7 but sometimes pentodes are used such as the 6GX6 used in the R-4. The second audio stage is a power amp, usually either a power pentode such as the 6EH5 used in the R-4, R-4A and R-4B, or a beam pentode (6AQ5) as used in the SW-4. There are a wide variety of triodes and pentodes used in audio circuits. There is little point in using a push pull audio stage in a communications receiver due to the restricted audio frequencies used. A push pull audio stage requires two more tubes - a triode phase inverter and a second output tube - plus additional capacitors and resistors so it was not cost effective for most applications. John, VE3PMA
_______________________________________________ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
