09-08-2017, 08:32 AM
Hi, all, I have a TV-11 that always seemed to test even very weak tubes as "good." The TV-11 is a simple emission, shorts, and noise tube tester, but many people consider it one of the better ones for finding bad tubes. I don't know much about that, but I like it because it is easy and fast to use for basic tube checks.
When I got this TV-11, I went through all the restoration procedures and fixed some obvious problems and calibrated it. Everything worked well, but I noticed that its quality test rarely showed a tube as weak—even those that I know test very weak on other good emission testers, show "replace" on transconductance tests, and are not good performers in their actual radio circuits. Just for one example, my B&K 667 showed emission of a 12SK7 as about 40%, Jackson 648 showed "weak" to "questionable," and the Hickok 600A clearly showed "replace." (These are all restored and calibrated testers.) The TV-11 showed well into the "good" range at 65/100. For comparison, two thoroughly tested new-old-stock 12SK7's read about 85 to 90/100 on the TV-11. Other old, weakling 12SK7 tubes also read "good."
As a side note, it's interesting that the TV-11 uses the same "load" setting (3) for most tubes from 12SK7 to 6L6. I'm not sure how well that works...but that's the way they designed it.
What I ended up doing was just adding some resistance in series with the 15K ohm resistor in the TV-11, between the quality test switch terminal and the lever switch bank. I didn't want to change the line voltage calibration because it would change the actual heater voltages that it applies to the tubes. That 15K is only in circuit when the quality test is done, and not the line voltage set-up. I hope this all makes sense. By experiment with several new and known weak tubes, I determined that adding a 1.8K ohm (in my tester's case) in series brought the readings down to where those new 12SK7 read about 75-80/100, a new 6L6GC read about the same, and the previously mentioned weak tubes read "replace" or "weak."
Anyway, I hope this helps someone who wants to use this popular old tube checker but has the same problems. I don't expect all testers to agree or be 100% reliable, but when you have tubes that you positively know are in pretty terrible emission and performance condition, you don't want your TV-11 to consistently tell you they are good.
Rob
[Image: https://s26.postimg.org/p9fzgr1q1/TV-11.jpg]
When I got this TV-11, I went through all the restoration procedures and fixed some obvious problems and calibrated it. Everything worked well, but I noticed that its quality test rarely showed a tube as weak—even those that I know test very weak on other good emission testers, show "replace" on transconductance tests, and are not good performers in their actual radio circuits. Just for one example, my B&K 667 showed emission of a 12SK7 as about 40%, Jackson 648 showed "weak" to "questionable," and the Hickok 600A clearly showed "replace." (These are all restored and calibrated testers.) The TV-11 showed well into the "good" range at 65/100. For comparison, two thoroughly tested new-old-stock 12SK7's read about 85 to 90/100 on the TV-11. Other old, weakling 12SK7 tubes also read "good."
As a side note, it's interesting that the TV-11 uses the same "load" setting (3) for most tubes from 12SK7 to 6L6. I'm not sure how well that works...but that's the way they designed it.
What I ended up doing was just adding some resistance in series with the 15K ohm resistor in the TV-11, between the quality test switch terminal and the lever switch bank. I didn't want to change the line voltage calibration because it would change the actual heater voltages that it applies to the tubes. That 15K is only in circuit when the quality test is done, and not the line voltage set-up. I hope this all makes sense. By experiment with several new and known weak tubes, I determined that adding a 1.8K ohm (in my tester's case) in series brought the readings down to where those new 12SK7 read about 75-80/100, a new 6L6GC read about the same, and the previously mentioned weak tubes read "replace" or "weak."
Anyway, I hope this helps someone who wants to use this popular old tube checker but has the same problems. I don't expect all testers to agree or be 100% reliable, but when you have tubes that you positively know are in pretty terrible emission and performance condition, you don't want your TV-11 to consistently tell you they are good.
Rob
[Image: https://s26.postimg.org/p9fzgr1q1/TV-11.jpg]
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