[barretter]

Yes, it plays back fine in mono and stereo and you can't really hear much of the noise in the left channel until the music stops. The strange thing is that today I installed a couple of new drive belts and now the left meter plays along with the music while the right meter is stationary. Presumably I must have disturbed something but I don't know what. Both meters kick on switch-on and the left meter reacts as the hum/moan noise builds up momentarily in the left channel. The tape/source switch doesn't have any effect in playback. I presume it's meant to be used for comparison purposes in recording mode, which I haven't tried yet.
The noise in the left channel disappears when I press the record switch but I suppose that means the noise is in the amplifier circuit.
I attach a picture of the inside : where would the preamp circuit board be? Many thanks