Mike -- The values you measured are quite normal. The rectifier design used in your amplifier is in fact full wave design, in that rectification is taking place on both halves of the sine wave. This is the very definition of what the term "full wave" means. What you are likely referring to (i.e.more familiar with) is what is known as a "conventional" full wave rectifier design. In this classic configuration, the HV secondary is center tapped and usually grounded, with the two rectifier legs coming off each end of the winding. Rectification can be either tube or SS rectifiers.
The Fisher circuit employs what is known as a Full Wave Voltage Doubler circuit, which has always been well known, but seldom used with vacuum tubes because of (usually) the need for multiple tubes, and the fact that early caps of significant capacitance and voltage were quite large. With the advent of SS rectifiers and improvements in electrolytic cap construction, the circuit then becomes highly practical, if not desirable: Transformer physical size for a given wattage output is reduced allowing for a smaller chassis footprint, regulation is better due to the lower impedance of the transformer winding, and less heat is produced over a similar conventional full wave rectifier design. In a full wave doubler circuit, the two diodes are connected in opposite polarity to the transformer winding, so that what is effectively produced is two half wave rectifier circuits connected out of phase, and in series, which then doubles the voltage. For the same DC voltage and current output from the doubler rectifier circuit, it requires only half the AC voltage input, but draws twice the AC current versus that drawn by an otherwise conventional full wave rectifier circuit of similar capability.
I hope this helps!
Dave
