What does the term push pull mean ? Can you push and pull them around real easy ? They must be real heavy. I have some freinds that will help move them.
Hi,
Push-Pull is a condition of two output tubes working in conjunction with each other. I will give a few of the pros and cons of PP and single ended operation.
1) Class B operation. This condition means each tube is essentially turned off during approx 1/2 of an audio cycle. In conjuntion with the OPT (output transformer wound in a certain way), one tube produces 1/2 the waveform and the other tube produces the other half. I guess one could say one tube produces the positive half and the other output tube produces the bottom half of the waveform.
2) Class AB1. In this state, each tube produces more than 1/2 half of the waveform but less than all the waveform. In otherwards, the tube is shut off for a portion of the cycle but not cutoff an entire half of the cycle.
3) Class A. In this condition, each tube produces all the waveform. In otherwards, the tubes never turn off. Each tube produces the "entire" signal, all the time. Kinda like two single ended amps with a means to supply both "sides" with a signal 180 degrees out of phase to each other and using the same output transformer.
I won't get into A2 and AB2 operation as they involve grid current.
The advantage of pushpull is the cancellation of even order harmonic distortions (about 40db or so), and more power output. Frequency response, at both extremes, is generally better than single ended.
The weakness is more parts are involved and more care needs to be taken for emotional involvement.
PP (pushpull) operation can sound as good, or better, than singleended because of the better extremes and as good of midrange, but one must design very carefully.
A few cons and pros of single ended operation.
1) OPT core saturation because of DC current flow through the windings. This causes a loss in bass response and higher distortion, esp in the bass region.
Parafeed operation means more parts plus the problem of OPT inductance change with amplitude of the signal, and possibly an additional coupling cap to keep DC current from reaching the OPT. (The lower the signal amplitude, the lower the frequency response with parafeed.)
However, a smaller OPT is needed with parafeed vs the typical tube to OPT connection single ended amp since no DC current is flowing.
Fewer parts are generally needed to build a single ended amp, so it is easier to make one that sounds good. PP is much more difficult.
Almost forgot, the output impedance of the PP amp can be more constant, in class A operation, than the single ended tube design. This relates to a more constant damping factor, better control over the speaker drivers as the waveform is reproduced.
Hope this helps.
