Keep in mind, the current on phone lines is limited to, guessing here, 1/2 amp. And that current is coming thru 22-24 gauge wire. (little wire, little current). 120VAC pretty much always can provide 20 Amps, 40 times as much current! And be coming to you courtesy of 12-14 gauge wire. (big wire, big current) The volts will bite in either case, (Defy you to tell the difference between 90 and 120 volts AC when you're doin' the joltage jump!

) In any case, you'll definitely blow up your '77' by putting it across 120VAC. In fact, if you sniff carefully, you'll probably detect the acrid odor of electronic oops. You may even hear the 'snap, crackle, pop' of destruction! Keepin mind that the little IC in there is rated for 18 volts or so. The components around it can protect it for a short (no pun intended) time, but constant 120VAC is gonna cook those little components (acrid electronic oops) and then the little IC is gonna go (YUP) 'snap,crackle, and sometimes for extra excitement, a BIG, POP! So, be kind to your work partners and they'll help you out of some tight situations. Or, be prepared to provide extra support to PE. John C.