Calibrating a tube tester?
 

For testing my tubes, I've got an old Seco drug store type tester. Always seemed to work pretty well, but I'd like to calibrate it, as there are a few readings I've looked at recently, but don't trust. There are controls underneath to do so.

Is there any secret formula for doing so, other than checking it against another tube tester and matching the emissions readings? I've heard mention of a calibration tube, but haven't seen anything for sale.

I've seen calibration tubes on ebay for Hickock but don't know what is special about them. Maybe a NOS tube or two would do the trick. I'm sure someone has more info than I do. Good luck with it.

The Hickok "calibration tube" is just an ordinary tube that has been aged and then tested at the factory on a particular model of Hickok teter. The test reading is noted on a label attached to the tube, and other units of the same model can then be adjusted to give the same reading as the "golden unit" back at the factory.

All the Hickok calibration tubes I have seen have been metal 6L6s, FWIW.

That said, even said calibration tubes have since changed in calibration.....

You can calibrate testers just fine without those tubes. Probably more accurately actually. Here are the instructions for the Hickok 600 for example.

I would just get a reading from a few different tube testers and make sure they are within an allowable difference. I built my own tube tester using a couple of different guitar amplifiers that allows me to get readings using a few different tube inputs. I work in calibration and I try to calibrate for what it used for to make sure you do not overcompensate. Good luck.