Troubleshooting: amplifier Musical Fidelity A1

Hi

I am the happy owner of one A1 amplifier, bought in 1991.
It is 20 Watt class A amplifier, build around MOSFET.

In the last months the A1 started to malfunction, the volume knob works very
bad: when I turn the knob I hear strange noise ("shhh shhh" as there is sand
inside the knob, and also some "crack") and the volume output isn't in
accordance with the knob position.

I took the unit to repair, but they said me they cannot because they haven't
the potentiometer.

I ask you:
1) is really the pot the culprit ?


2) where can I found one (or two) spare parts?
It is a Alps 0071 50KAX2 (I cannot measure the value because it is
soldered).


3) by the way, do you know which are the exact final transistors?
I found on newsgroups many codes:
original: A1 N8915 and A1 P8919
poor quality? 2N3442 and 2N5876
good ? Motorola MJ15003 & MJ15004

My unit (model A1 X) has these transistors:
A1N9020 A1N9034
A1P9022 A1P9018
I don't understand why are there four different codes instead of two exact
couples!


4) which are Musical Fidelity address, Emai and phone?

ciao, Massimo
Italy