You don't want to go poking around inside a tube unit. But, can you see the tubes with the unit powered up? If so, are any of them obviously dead? Any big black spots on the tops?

It's possible you simply blew a $15 tube and fuse. If you've got a high end shop in your town, they can probably diagnose the problem rather easily...for a fee.

In part, yes, the tuning function is controlled by those tubes. If the tuner has been is storage for awhile, the chances of a bad capacitor are more likely. Even if the tuner has been in use but not serviced lately, a bad cap is still most likely. You'll probably have to find a technician who will service tube tuners. The voltages inside a tube based tuner are lethal and not the place for someone without sufficient knowledge to be poking around.

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You don't want to go poking around inside a tube unit. But, can you see the tubes with the unit powered up? If so, are any of them obviously dead? Any big black spots on the tops?

It's possible you simply blew a $15 tube and fuse. If you've got a high end shop in your town, they can probably diagnose the problem rather easily...for a fee.

I remember going to Lucky's as a child and playing around with the tube counter/cabinet. It had sockets on top so you can figure out with your dead tube which new tube to take out of the cabinet below it. Now you have to go to a high-end shop for a vacuum tube? Isn't there an old surplus or something?

You might give this guy a try. De Wick Repairs