12-01-2021, 12:47 PM
Yes, the 71A tubes are getting expensive. The cheapest I can find them on eBay is $18 plus shipping for good tested tubes. I advise you to check the filament voltage at the socket before you plug anything into it. The 71A has a 5 volt filament, so the voltage between the two fat pins should not be much above that. It can be AC or DC according to the spec sheet.
[Image: https://64.media.tumblr.com/aede1094fb9b...2e5b49.jpg]
You can also check the DC voltage from the plate to the filament, then check the grid bias voltage, and compare them to those shown on the spec sheet to see if they are in the ball park. Beyond that, about all you can do is hope for the best. Good luck.
[Image: https://64.media.tumblr.com/aede1094fb9b...2e5b49.jpg]
You can also check the DC voltage from the plate to the filament, then check the grid bias voltage, and compare them to those shown on the spec sheet to see if they are in the ball park. Beyond that, about all you can do is hope for the best. Good luck.
