Hi Bill, just a thought regarding high voltage readings... Fender amps are shipped with the mains tx set to 230V, our mains down here at least, often reaches 253V, so you need to reset the transformer wiring to 240V if possible. You say it's a 1979 model in which case it may not be possible
Here's a short video of what you need to do (and if your model will allow)
https://www.youtube.com/watch?v=7fw58fj-z8c&t=141s