Hi, I don't know if you're still interested in finding a solution...

If you take a look at the circuit (available here: http://www.ozitronics.com/docs/k64.pdf)
you'll see, that R9 (10k) is way too high! Just short-circuit it. Also, R8 (10k) is too high. Replace it by a 1k resistor.

Both R9 and R8 resistors are responsible for a reasonable current on the microphone. In the original circuit, the current is definitely too low!

Merry Christmas!