[Techman]

There really is only one correct answer to this question and that is as has been said, to connect one channel to one of the outer speakers and the other channel to the other outer speaker, leaving the middle one not connected. It’s a bad idea to leave one channel of the amplifier connected to a dummy load, as if a fault were to develop in this channel, you’d be unaware of it until the smoke started to rise! And talking of rising smoke, has that amplifier been serviced recently? The amplifier will need some inspection BEFORE any attempt is made to power it up. This may not be too much of a problem, as it will probably only require the replacement of 4 paper capacitors in each channel for safety and reliability at a cost of a fiver or so to you. There will be others, but these may not need replacing as they’re not in critical positions and the electrolytic smoothers may well prove to be fine.

Some things to keep in mind – don’t make the fitting of the amp too permanent, as an original type may turn up one day. The output from the Rogers amp may be a bit too powerful for those speakers individually – not a problem if you don’t run it flat out! If you’re worried about the power handling of the speakers, you could always put a bit of series resistance in line with each speaker and then some parallel resistance across the whole lot to adjust the impedance on each speaker. The resistors will need to be ‘watty’ types, values to be decided if you want to go down that path.

As a last thought – you could always electrically immobilise one of the amplifier channels – i.e., remove HT and heater supplies from one channel, but I think that this may be a task too far for you at this moment in time.