A subject that I felt needed a thread of its own. There's a fair bit of misinformation about the trigger voltage of older flash equipment. Mainly caused by people not having the equipment or skills to properly measure it. The issue is caused by the high series resistance of the trigger circuit used in most older flash designs. Here's a quick sketch of a typical trigger circuit used from the 1960s to the 1990s: Vx is the unknown trigger voltage we're trying to measure. Rx in the diagram is there to prevent the flash trigger connector from killing you! Or at least prevent it from giving you more than an uncomfortable tickle. The resistor needs to have a high resistance value to do this - usually several megohms. So just poking a 10 megohm input-resistance voltmeter onto the P-C connector or hotshoe won't give you an accurate voltage reading; not by a long shot. The reading you get will be low by a fair fraction of the true voltage. There are at least 3 ways around this, but only one of them is cheap to implement. 1. Use a very high input impedance electrometer. These are rare and usually expensive bits of kit. 2. Use a reasonably fast storage oscilloscope to 'grab' the peak voltage before it decays. Also expensive if you don't already own one. 3. Use a cheap 10 megohm input resistance digital meter, and add a 10 megohm resistor (costing a few pence or cents), plus a bit of maths. These are the steps of option 3. Take a straight reading of the trigger voltage with the meter. Call this V1. Put your 10 megohm resistor in series with the meter and take a second reading through the resistor. Call this V2 Done! Apart from a bit of long-winded maths. To find Vx, the unknown trigger voltage, you can use this formula: Vx = V1+(V1*(2*V2 -V1)/(V1-V2)) I've used spreadsheet notation so you can easily copy it across. Case study. Here's a flash that has a particularly nasty high voltage. V1 on this beast measured 204 volts. You might think this would be safe on your 250 volt rated Nikon.... wrong! Because V2, with series resistor, measured 129.4 volts, and if we plug those numbers into the formula we get Vx = 353.9 volts. Ouch! Not safe on your Nikon at all. Just to verify that the method works; here's a storage 'scope trace of the open-circuit voltage quickly decaying as the 10 megohm 'scope probe is applied. You can see that the instantaneous peak hits over 350 volts (Y=50 volts/division, X=50 ms/division) The voltage discharges to just over 200 volts in 1/3rd of a second. Too fast to be caught by a cheap DVM. Once you know Vx, you can also work out the value of Rx if you care to. In the above case it's 7.35 megohms. Well, there you have it. That's how to accurately measure the trigger voltage of that old portable or studio flash. FWIW, the hotshoe adapter shown alongside the Sunpak AZ3600 does drop the trigger voltage to just over 12 volts. But the P-C connector voltage is still at 353 volts.