I found a listing on ebay for a 6hr6 vacuum tube. The unit used to test the tube is a Hickok 6000A tube tester. The average new value on the roll chart is 3600 for this tube. They listed the min for the tube at 2160. Is there any way to find out how they got this number of 2160 as the min good value for this tube. Any suggestion will be a big help. As far as I know there is no min value for any tubes except diodes which would be 800 at the diode ok mark. Thanks