Hi Pat!
My friend just show me this amplifier recently and this is capable 64 ohm.
http://mcc.berners.ch/power-amplifiers/MC3500.pdf
Is that ok as I come across an used pair with reasonable price?
I cannot test the amps here and give a health check in writing. That is the work of a serious professional. These amps seem to have much higher power capability than anyone I know would ever need, so I wonder WTF you wish to buy them.
If there is anything wrong, it could be expensive to fix them. The McIntosh were world leaders in OPT construction methods and the MC3500 are able to drive the rated output power into a large number of loads between 1r0 and 64r. Providing you have the correct number of load ohms connected to the outlet labelled for those ohms, or near to that load outlet, all will be well. A 64 ohm speaker can be used on any outlet labelled with lower ohm load, but you MUST NOT use a lower speaker load on the outlet labeled higher. For example, DO NOT use 8 ohms connected to a 64 ohm outlet.
I am not aware if the 3500 has multiple outlets which are taps off the OPT secondary windings or if the secondaries are in fact multiple windings which are strapped to suit many different speaker ohm values.
READ the MC3500 MANUAL. If you get smoke, don't blame me!
Patrick Turner.
Regards,
J