In my experience Altec gear is really bad news in the hum and buzz department. I often end up jumping through various hoops to get the noise down. I think they were inconstant in their grounding schemes. In some cases I've had good success with rewiring to achieve a star ground. Good luck with the beast.
Bill's answer makes a lot of sense, given the lack of rhyme or reason as to who gets a usable one and who suffers with incurable hum/buzz. Line voltage levels vary from location to location and even building to building. And they are uniformly higher than they were when these things were designed/sold. I've been watching this thread angrily and that's the only answer that makes sense to me.
Interesting, I didn't know either. Funny that the file name for the map I attached shows the traditional "L" and "R" confusion in translations. Anytime I've visited, I my nickname "Bill" is usually pronounced as if it were spelled "Beer" - always makes me smile!