Mission Cyrus 2 high frequency 'whistling' problem
 

I have a problem with my Mission Cyrus 2 amplifier, bought in the late
80s. Recently it's started producing a high-frequency whistle, which
has the same intensity independant of the position of the volume
control. Speakers are Mission 753s, but I've tried it 'in isolation'
from the rest of the system attached to small Denon speakers, no
inputs, and it still makes the whistle. On switching off the whistle
persists for some 10 seconds or so.

Anybody have any idea what might be causing this (problem with the
power supply, problem with the amp,...) and what might be done about
it. The amp has given over 15 years solid service, but is now pretty
clogged with dust, which I suppose may not do it much good. I've also
had the top off (to try to clean the imput selector, which was
producing a fair amount of noise in some positions) but managed to get
it back on without having any spare parts left over, could I have
knocked something out of position then to cause the problem?

Any help/advice gratefully accepted,

Colin Mahoney

Monistrol de Montserrat
Catalunya