Martin, Sorry for not getting back to you sooner, and many thanks for the advice. I eventually got around to pulling the top off and having a good look at the Tuner power supply circuit. It is fed from the 60v supply and TR10 (BC212L-B PNP) appears to be the controlling device. The 22v Zener diode (Item 138) that you described (which is marked ITT ZF22

Thanks Martin, I wil let you know how it goes when I check that Zener and its heatsink paste. think I will monitor its voltage over a period as well. Richard

I have a Beomaster 3000-2 FM Tuner / Amplifier, owned and used continuously since new in 1970. I have made various repairs by replacement of electronic components (mainly electrolytic capacitors and low-noise transistors) over the years but need help diagnosing a recent fault. When switched on to FM tuner, after a few minutes the frequency wanders off