Or, it could be something as simple as the wrong safety capacitors in the input line, for example if it had .01uf caps it it when it was built, do NOT put the same value in again, it can give you a slight shock if they leak, the have much safer lower value x2 safety capacitors now that are made for that job.
not sure what you have in yours. but here is info
https://www.justradios.com/safetytips.html
it's for Radios, but it applies