An amplifier with a push-pull topology is characterized by a power stage in which active device pairs work together amplifying the positive and the negative signal half waves separately. The output transformer, therefore, reconstructs the amplified signal and makes it available at the output terminals. The main benefit of this topology is to design amplifiers which have a much higher power than their single-ended counterparts, even when using the same power valves in the output stage. This results in better efficiency, which also means a significant reduction of the dissipated heat at the same power rate.
Nevertheless the push-pull stages, because of to the simultaneous action of two different devices, need very careful design and set up to avoid the large distortion that always occurs when the amplification of the two half waves is not equal. The P-70 is an amplifier capable of delivering more than 70 W per channel into a 6 Ohm load, with a THD lower than 0.2% over the whole audio band. In this way its performance is comparable to those of a well-engineered single ended amplifier. 

Note: The glass of P40 and P70 is made in one piece, and not all colors are always available.