I have a question, if anyone would like to educate me. I have my father's fairly large, old Grundig AM/FM/SW radio. We have had it ever since I was a baby and it's like a family member. It has always worked beautifully and I used to use it daily for hours on end in 2012 to listen to FM when I lived on my own and was very lonely. It has not been plugged in or turned on for about 4-5 years right now. What is the maximum time duration a person should let an old tube radio sit unplugged and unused before they need to be cautious and use an isolation transformer and variac to slowly apply current to the circuitry again? In the past, I've always plugged it in and turned it on with a hand ready to pull the cord if things went bad. My dad had always told me that turning on old radios after a while was stressful for them, but I didn't know just how dangerous and risky it can be until now. My dad died 3 years ago. I can't call him and ask this type of question anymore. I'd be absolutely gutted and heartbroken if that radio exploded one day after plugging it in. Thank you for reading my question.