What is the maximum time duration a person should let an old tube radio sit unplugged

[hyuna]

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.

[Robh3606]

Sorry can't help you. I would think you would get a quicker answer here:

https://www.diyaudio.com/forums/tubes-valves/

Rob

[Doctor_Electron]

Another place, great forum with great people...
https://antiqueradios.com/forums/index.php

[SaturationPt]

There is no exact answer. If it has never been serviced, the capacitors and resistors as well as tubes are up to maybe 70 years old?

They could be on the brink of failure, might last years longer. It stresses electronics to turn them on whether they've sat for an hour, or for a year and that is part of why failure during the initial power-up is more common than while operating. The degradation however of components and failure can occur while you're happily listening and have had it on for an hour, this is why there really isn't a catch-all answer where it can be said that it is safe to turn it on if it hasn't been stored / off for more than x days or x years, even x hours. I have a pair of tube amplifiers that I bought after nearly 50 years of storage in a Chicago garage, they powered up on a variac/DBT and after some settling time I put music through them, sounded great (then off to the bench for a total service/restoration of course). There is no way of knowing unless something is obviously leaking or heat-stressed.

The best recommendation is to have it serviced. The most likely failures would be electrolytic capacitors or aging resistors but a tube can "red-plate" also and damage bias resistors etc if it fails. Once properly serviced you will be able to power it up and down at a whim and enjoy listening to it, not worrying about whether you might let the smoke out of your Father's cherished radio.

[Kay Pirinha]

In my youth I used to just plug in radios of even unknown origin and see what happens. Well, that's almost half a century ago, and »old« radios were almost half a century younger.

Today I'm quite a bit more cautious. I always connect a radio of unknown condition via a mains bulb tester first. This is an incandescent lamp of 100 watts that is in series with the mains. If a tube radio is powered on, the expected behaviour is that the bulb first glows rather bright, then goes almost dim, and finally a littler bit lighter again. The first bulb flash results from the cold tube cathodes and the high heater inrush current. During the warm up period current draw decreases, bulb gets dim. Finally, if the cathodes are warmed, plate draw starts, resulting in a brighter bulb. I let the radio turned on for some hours. If nothing changes, I connect it directly to the mains.

Anything else, especially an always bright mains bulb tester, shows that something must be wrong with the radio.

Have success!