OK, you have a killer flash....now what? Well you have a few courses of action:
Throw away the flash. Bad for the environment, bad karma.
Give away the flash. OK if you make sure that unwary recipient knows that the flash can destroy a modern camera. Look for the Holga and other toy camera users. All that plastic will be unaffected by the hundreds of volts coursing through its guts.
Get a limiting device. Wein Products Inc. sells
a very nice hot shoe voltage regulator. For $50, this product will protect your camera against high voltage flashes. However, you do sacrifice all the communication you might have on the flash as well. Usually not a problem. Most flashes with communication electrodes are modern enough to have a low trigger voltage.
Get a PC limiting device. The flash plug (PC plug [PC stands for Pronto Compur]) will carry the same trigger voltage as your hot shoe only flashes. You can also buy
PC connection cords that will limit the trigger voltage.
Practice good flash hygiene. Properly label your flashes and only use the correct flash with the correct camera.
Surgery. If you are "good with tools" you might want to open the guts of your flash and install a trigger voltage limiting circuit like Zenobe did with a Vivitar 283
. It is not as hard as it sounds, but there is an element of danger. Flash capacitors can hold literally heart stopping voltages. Make sure you observe all safety precautions and never trust a capacitor. Always handle capacitors like they are fully charged, a little paranoia goes a long way.
If you don't want to or don't have the equipment to measure the trigger voltage on your flash, you can look here
for a database of flashes and their trigger voltages.
Enjoy your well lit photos with a flash you can trust!