Not unusual to have background hum in the speaker. It's still better to replace electrolytics in a transceiver 40 years old.
Norm
:Hi all I picked up this six meter transceiver at a hamfest in Delware today [ very nice weather today by the bay ] anyway got it home hooked up to variac after clean-up . I got it up to around 85 volts over the course of two hours. No smoke, but there is a slight hum in speaker I guess my question is does a hum in the receiver alway indicate [Dooms Day] for electrolytics. Regards