When I was running my ST-70 up on the Variac after just acquiring it, I kept a DC Volt meter clipped to the first cap section on the can capacitor; even at 130 VAC input to the amp, I did not exceed the WVDC rating of the first section on the original cap. Nor, did I ever exceed the WVDC rating on the subsequent sections of the cap.
When I spoke of not being equipped to check the cap at working Voltage, I should have been more explicit in indicating that I was referring to checking it for capacitance values at working Voltage. Again, I had no evidence that the capacitance values weren't up to spec, I just had no way to check them.
We all think of AC line Voltage back in the day as being lower than what we receive today, and perhaps, generally speaking, that may be true. In reality, though, they could also run considerably higher, especially out in the sticks. I'm guessing that designers of the era took that into account. IIRC, DeWalt designed their radial arm saws to run properly on a range of input Voltages from below 100 VAC to upwards of 150 VAC at the top end, precisely because they had them in the city and the countryside, and were aware that the actual Voltages delivered at various times of the day in various venues could be all over the map; so, they designed for an approximation of worst case, based on the available data.
I suspect Dyna built in similar safety margins for their designs, since they intended them to run anywhere as well.
Again, after bringing it up over a period of about 10 days on the Variac, mine ran perfectly on my line Voltage of 125 VAC for many weeks before I replaced the can cap.
