The clue is still the fact that the problem evaporated when you
disconnected the speaker cables.

That implies that the injection was either

1) common mode on the speaker leads. If so using a suitably ferrite block
in common mode near the amp sockets should reduce it.

2) Differential mode - probably because the speaker coils were picking it
up. In which case you might need to apply a shut cap near the speakers.
(potentially more problematic for the amp, of course.) And/Or a
differential ferrite near the speakers.

Jim

In article , Brian-Gaff
wrote:
No I remember having some from Tandy at that time and no difference. I
could vary it a bit by routing the cables of course, but also if I then
placed a hand on any connected item even if earthed to the mains, I
could change the level of it.

I suspect that the transmitter in question had harmonics oll over the
place and as I'm not far from the Thames as the rf flies, the whole
wiring and house was an aerial, and it just happened to be a coincidence
that thee amp had poor rejection at one of these. The fact that the
pioneer was fine seems to suggest there is better screening less earth
currents and possible better filtering.

It had little coils in the output stages, well quite big ones actually.
Nothing like that in the Tandberg just lots of heatsink. Brian

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