[Ron Ramirez]

...most output amps, even those with one supply are designed as DC amps with DC blocking caps at input and output if one supply and none with dual supply (and differential amp for the input stage). They are also frequency-compensated to be stable and this in a well-defined amp does not depend on whether the load is there or not.

...yes, but...

We're talking about 1965 when high fidelity transistor amps were still in their infancy.

And to make matters worse, half of the eight output transistors used in the TX-300 are germanium! And there are no blocking caps between the output transistors and the speakers in this amp.

This was technology that was still developing.

Here's a food for thought: many if not all transistor amps have the button that disconnect the speakers.

None of my Fishers have such a button...and neither does Kirk's friend's TX-300.