I’m only finding one company that claims to do vintage system repairs - along with flat screen TVs and such like. Perhaps they could advise me at either a music store or the local used record shop?
This is even more of a problem with equipment that uses a bridge rectifier (although tube equipment, unless hybrid (if direct line connected without a transformer), won’t use one) - since there is no safe way to orient the plug without the chassis (or primary ground) becoming live, including virtually all modern electronics since they use a switchmode power supply, which also happens to usually have a capacitor connected between primary ground and secondary ground for EMI suppression (the bridge capacitor shown here), although the capacitor has to be a special type rated to withstand multi-thousand volt spikes and not fail short.
Would the whole wiring issue be safer if I plugged it into a surge protector instead of directly into the wall, by the way?
<shuffles feet>
Aw, shucks Ma’am.
</shuffles feet>
if the cord can be replaced by a polarized cord (this would require the cord to be mounted correctly on a back for the unit) it would be safe.
a skilled hobbyist or technician could do this and other repairs if you can’t.
No. Makes no difference at all. An RCD protector would however guard against most accidents.
A good place to get something like this looked at would be a guitar amp repair place. Any tech that works on tube based guitar amps would be very familiar with the issues.
I would not feel at all safe with the original components - especially if there is a death cap (which there most likely is.) As Michael63129 notes, there are modern capacitors that are rated for this use - they are the X and Y rated capacitors, and are specifically designed to survive safely in the face of mains voltage spikes, and have a self healing design, so they won’t fail to a short circuit. Y rated capacitors are designed to sit between line and ground, and a Y2 capacitor has an impulse rating of 5000 volts. Y2 is what should be used in your device, if the capacitor is to be retained, and the chassis left floating. However getting a tech to look at it would be the right start, as only by looking at the specific design can one really know what is needed to ensure it is safe to modern expectations.
You’d need an isolation transformer (like this one) if you wanted to be sure that you couldn’t get shocked - and even then, only if you were touching something grounded and the stereo, as opposed to two points inside the stereo (a RCD/GFCI wouldn’t help either in this case since it detects leakage between line and ground). Same for a UPS, unless somebody makes a model with an isolated output (tube equipment is much more robust against surges anyway).
As previously said, the best option would be to obtain/make a new back, or keep it close enough to the wall that nothing can reach inside, but ventilation might be an issue; the plug problem can be fixed, as also said previously, by replacing it with a modern connector or even permanently connecting the cord (the original back was designed so it would unplug when removed, a new back can be made with a cutout to fit around the cord).
Well, I could certainly make a new back - I could just command adhesive some cardboard onto it for the time being if that wouldn’t be a fire hazard and then if I wanted to do something permanent I’m sure I could do pegboard or something.
The original backs on stereos like these used 1/8 inch masonite hardboard with ventilation slots. If you make a temp cardboard replacement, include a few slots - a couple of them a half-inch high along the top and bottom edges should do fine.
I mean, it just needs to keep kitties and hands and some of the dust out of there, right? I can definitely do that with a utility knife tonight.
ETA - I’d really like long term to have it restored, but first I want to see what I’ve got.
you could make a temporary back with cardboard or paper with a bunch of ventilation holes in it (maybe 5% of the area). you would want to put tape on wires with cracked insulation, cut some electrical tape a few inches long and wrap, move the tape not the wire (the old insulation may be brittle and crack more if you handle it too much).
for use beyond a short test you want to have the cord with the neutral wire to the correct pin on where the cord plugs in (a person would need to look inside the chassis). touch only wood or plastic knobs/levers/switches, don’t touch any metal.
it may need some old parts replaced and old wire replaced to operate except for a short test. it depends on when it last was in use, it may need repair to work at all, old capacitors or broken insulation on wires may cause it not to work.
Why? I mean, copper prices have gone up, I’m cheap as hell, and I have a bit of a death wish, but there is no way in hell I would tape a wire with cracked insulation instead of replacing it!
Or skip worrying about how to figure out the correct pin and touch (don’t grab!) the metal chassis. If you get shocked reverse the wires. But this might just be what happens when a person who is always in a hurry has a death wish.
I don’t recall the cheater cords my Father used for TV repair having any “polarity”, and the outlet plugs had no difference in their pins to plug in one way or another. Ground the chassis and gently plug the power cord into the wall. 
i was speaking in terms of just wanting to test it before doing a repair.
I would expect (but certainly not assume) that for an appliance with an unpolarized plug, made in the day of unpolarized outlets, that neither pin would be connected to the chassis through a low impedance path.
Was this not the case? Was one of the pieces of advice regularly found on Ye Olde Message Boarde (which was an actual wooden board) “If you’re getting shocks from your appliance, try rotating the plug.”?
Yeah, I mean, it’s made to be plugged in like this, right?
This is correct - but the problem is that there is usually a capacitive coupling - and that capacitor (now often called the “death cap”) is known to fail. These devices were made before the days of self healing, voltage spike resistance, capacitors, and whilst rated for the base voltage, would not resist spikes on the mains, or were generally not as well made as modern capacitors. They can and did fail to a short circuit. Hence their name. In the vintage guitar amplifier arena these capacitors are rooted out as a matter of course. Of course a failure of the capacitor when used with an electric guitar can mean that the strings on your guitar become live - which is significantly more likely to bring about a swift demise than the chassis of a radio inside a box going live - but neither are safe.
Now that is scary. Did it happen often back in the day?
Keith Relf of the Yardbirdsis the name that comes to mind for me, although I don’t know if a “death cap” was involved. There’s a link in the references to a page with a few others, although not all were electrocuted while performing.
You should have put this in Cafe Society. Then you’d get more answers about guitarists who were electrocuted.
(Kidding!)
Killed at home. That is weird. I would have thought improper grounding at an outside concert.
Did he get 220v at the pickup? What kind of amp was he using?