Photo Meters backside, stacked one over the other. When I tried to get a V read my 30 year old plus Fluke kinda died. Might be 24V though, this was in the parts list.
You need to pull one of the bulbs and search by images on the web. For sure many amplifiers share this same bulbs.
Seeing that you got no other answers, means there aren't AK members who know the kind of bulbs your unit has.
If voltage is too high you can connect a resistor in series or a diode in series to drop the voltage. But that's a next step. Perhaps with the bulbs installed voltage is OK.
Thanks. Here is a close up of the backside of the meter. It would appear the bulb is inside the meter housing, making removal more difficult. I will remove the meters for closer inspection.
It seems to be a bulb like this one, you'll need to disassemble the VU anyway to replace it. Or, if you don't feel confident to do that, you could connect a LED with a resistor from the back of the meter, it will light it from the back.
(RANDOM PICTS FROM GOOGLE SEARCH, NOT MINE)
Some meters have sockets for the bulbs, no soldering needed, you can check if your's have:
I pulled the meter. No visible bulb. So it must be in the white housing. I'm not sure if I will be able to separate the face plate from the white housing,
Last image shows the stereo light bulb mounted in some sort of rubber boot.
I don't think those meters have any light inside, I see just 2 wires to carry the signal, there should be 4 wires if a light bulb were inside (2 for the signal, 2 for the bulb power)
I don't know if this AA 8500 ever had lights for the meters. It may be possible that the early 8500's from 1971 just came without lights. The reason I thought it should have lights is that I saw this one from radio museum with meter lights. Each of the two meters on mine have only two wires.