My 1964 Zenith has a rebuilt Sylvania CRT. I have an Accurate Instrument tube tester with CRT emissions test capabilities. Before I go on, I will note that this set has not been powered up in around 25 years and has not been used since the 70s until I brought it home several months ago. Anyway, when I performed the test the red and green guns were immediately strong, but the blue gun was not really bad, but much weaker than the other two. I have read stories about long dormant tubes sometimes taking some time to pop back to life; I hope that is my case! What I did was bump the filament voltage up to the next setting for maybe 20 seconds on the blue gun. Naturally, that bumped the reading up and I feared that it would just settle back once the correct voltage was re-applied. Well, it did settle back some, but what I did appears to have helped a lot! The blue gun now maintains a higher reading.
In summary, I guess I am wondering if the blue gun is often a bit weaker perhaps because it bears more heat than the other two being positioned on top. The Accurate tester is a bit confusing because the instructions say to use the "diodes ok" scale which is almost ALL in the green except for maybe the first 1/4" of needle deflection which is red, or bad. ALL of the readings were far from the red from the beginning. I prefer to look at the numbered scale for comparison purposes. The blue gun reads maybe 45, where the other two guns read like 60, but going by the instructions the tube is deemed good either way. As long as I can achieve a good color picture I will be satisfied, but I don't want to put any money in the set if the tube is on it's last leg.
It's funny that nearly all of the section tubes are stock Zenith tubes, but the set ran long enough to go through the original CRT. Perhaps the local repair shop used stock replacement tubes.
