The 36 VAC is used to derive an internal -29 VDC for the high score
table so it is not required for the game to work.
For audio amplification I used an LM380 2 watt audio amp chip
available from places like Digi-Key for under $1 as follows.
Pin C from Dig Dug board to one side of 10 K (volume) pot and the
other side of the pot to ground. Center tap of pot to pin 2 (of
LM380). Pins 7 & 3 ground. Pin 14 to +12 VDC and .1 uf from pin 14
to ground (decoupling cap). Pin 8 (output) has 2.7 ohm in series
with .1 uf to ground to prevent chip from oscillating. Positive end
of 250 uF electrolytic to pin 8 also. Negative end of cap to
speaker and other speaker connection to ground.