Instability in the amplifier sections at high volume levels, evidenced by whistling noises from the loudspeakers when adjusting the volume, were as a result of noise spikes on the +8V supply. The cause was 2C14 (10uF 16V), which was open circuit. The Beomaster 5500 seems particularly prone to these sorts of problems (see an earlier entry concerning noise on the -12V supply) but the tones produced are sometimes above the normal range of hearing, however if 2R231 and 2R431 (4R7 1/2W) appear to have been overheating this indicates that something is amiss. An oscilloscope check at the loudspeaker output with no sources connected will reveal if there is a problem, ensure this test is done at all settings of the volume control. [Beomaster 5500]