What is this? THERMEGUARD AMPLIFIER?

[Audio_by_Goodwill]

First time I've seen one of these..... what is it?


RARE VINTAGE ALTEC LANSING 128B THERMEGUARD AMPLIFIER - eBay (item 370204381335 end time May-27-09 12:03:53 PDT)

[Russ Farrell]

Thermeguard was a thermal-type circuit breaker inside the power transformer windings. It would cut off if the temperature got too high, and then automatically reset when the temperature of the transformer windings fell back to normal.

The 128B was rated for 40 watts @ 2% t.h.d. from 30 cycles to 20 kilocycles (Hertz was still just a family name in those days). Tubes were two 6CG7, two 6CA7 (or EL340), and a 5AR4.