06-16-2014, 04:08 PM
You really should not rely too heavily on what Tube Testers tell you, other than shorted, gassy, or open filament. The ultimate test is, DOES IT WORK satisfactirily in the circuit? I knew a store that made its living selling tubes. People brought in their tubes for testing (Mostly TV) About two out of five tested 'bad'. During a slow week, they could 'thump' a short into most miniature types. But mostly they were not in the circuit with the problem! Low emmission is not NO emission, and a tube that is not carrying a fair amount of power (audio outputs and the like) may have more than enough to operate in your radio.
Try swapping a known good one for the one that seems not
so good in the tester. No difference? Leave the 'bad' one in. Difference? Change it.
Example: the 7F8 in Philco and Zenith AM-FM sets. A brand new one will result in near 'ZERO' emission inside a week. But it will continue to work for a VERY long time.
Hint: In a TV set, keep the original IF tubes as long as possible. (usually 3) They aren't very costly, but replaceing them messes up the alignment of that IF strip. Internal capacities vary from tube to tube, and even more manufacturer to manufacturer. To a lesser degree, the same thing happens to your F.M. I.F..
Try swapping a known good one for the one that seems not
so good in the tester. No difference? Leave the 'bad' one in. Difference? Change it.
Example: the 7F8 in Philco and Zenith AM-FM sets. A brand new one will result in near 'ZERO' emission inside a week. But it will continue to work for a VERY long time.
Hint: In a TV set, keep the original IF tubes as long as possible. (usually 3) They aren't very costly, but replaceing them messes up the alignment of that IF strip. Internal capacities vary from tube to tube, and even more manufacturer to manufacturer. To a lesser degree, the same thing happens to your F.M. I.F..
