I think it is a BY127 but check the voltage drop across the good ones to make sure they are silicon and not selenium.
I'm speculating that these are Tunnel diodes
=MoolyNot tunnel diodes. These are standard rectifiers as everyone has pointed out.
The striped end of the replacements should be where the + symbol is on the diagram.
(That puzzled me no end as a youngster. If the cathode of the diode has the stripe, why do diagrams put a + marking there)
Tunnel diodes? I think not! TDs are low voltage (and delicate) diodes with a "snap-back" reverse characteristic, much used in trigger and oscillator circuits.
The schematic shows 50/60Hz HV rectifiers, as already suggested.
No, No, No...
Although the BY127 and 1N4007 would work, the BY127 is harder to get in the US and the 1N4007 way too common. As the original power supply looks like it used an obsolete metal can gold plated rectifier you will need special diodes available only through me for $85.00 ea. plus shipping.
Pay no attention to the 300 volt rating on the power supply capacitors and the stacking arrangement (Voltage doubler) that was used to get by with the lower voltage diodes back when the amplifier was built. Buy the special diodes quickly before I have to raise the price..