The SM-B201 has 19 tubes, which includes the two 6E5 eye tubes. Each channel uses a 12AX7, driving a pair of 6BM8's in push-pull output. 5AR4 rectifier. The filaments of the 12AX7's are supplied via DC from a separate power transformer winding, rectified by a germanium diode full-wave bridge rectifier with a R-C filter network, which also supplies the fixed-bias for the output tubes. The separate MXA-1 multiplex adapter, which I mentioned above, uses a matching cabinet and has three tubes. Pioneer later issued a model MXA-3 multiplex adapter, but I am unsure of its tube lineup and whether or not the cabinet matched the SM-B201. Of course, similar early 1960's external multiplex adapters, such as manufactured by H.H.Scott, Fisher, Marantz, Pilot, etc., would also work fine with this Pioneer.
VANADAR, mine sounds OK but needs a little work. Cosmetically it is excellent and super-clean, but in a brief bench test audio is a little muddy and somewhat less gain than it should have. I tested it hooked up to a pair of H.H.Scott S-10B speakers (c. 1969), but the speakers are not the problem. I suspect there is some leakage of the audio coupling caps which is upsetting bias on the output tubes. The Toshiba paper-oil coupling caps which Pioneer and other Japanese manufacturers used in their early sets are known to be notorious for leakage, and I plan to replace them in the near future. Also, I have not tested the 6BM8 output tubes yet, or the 12AX7 drivers, so that could also be a potential source of trouble. Although the power supply seems OK, I also plan to replace the electrolytic filter capacitors as "preventive maintenance" to safeguard the power transformer and rectifier tube in case these 45-year old filter caps should short. I am certain that once this Pioneer is recapped and the tubes checked, it will be a great performer.
Poston