And you're right it's really a reverse polarity switch.
Simply reversing the the plug on old amps without a switch did basically the same thing, before the polarized and 3 prong plugs came out.
I've rewired several houses which had the old 2 prong outlets, it's amazing what you find in the walls of some of these houses.
She was just too loud and I could never get a word in edgewise.
Unfortunately I dumped her and am now happily dating a '67 Bandmaster and a '73 bandmaster reverb. SIf she ever asks if she's too heavy, change the subject.
I discussed the reason for the re-issues' lack of an AC convenience outlet elsewhere on this site -- use the search function to locate the post.
Arjay_________________"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKYWhen I get a chance I'll check one of the reissues out and take a look at the ground switch.
Note that speakers also use the same type of date code.
Always remember that pots, speakers and transformers may have been changed!!
If three digits are present, the first digit would refer the units of the year i.e. If four digits are present, the first two digits refer to the year i.e. The last two digits would refer to the week of the year i.e.
("26" would mean the 26th week or approximately June).
The first letter is the year (A=1990), and the second letter is the month (A=January). You might have to remove the chassis to be able to see the sticker, or use a mirror on a telescoping arm.