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In Reply to: RE: Tester issues posted by nick-seattle on June 15, 2012 at 17:27:43
and on the Hickok, you could have a failing carbon resistor or a cap that needs to be replaced. Could be a number of things.
The Elaborate DAC=Johnny's Balloon Meshplate 27 Balanced Preamp=Balanced Six Pacs=Newform Research 645
iRiver H140/MB Balanced dac/amp/Ultrasone Ed. 9/JH13 Pro IEM's
see images at: www.pbase.com/jamato8
I don't think it's contacts since I tried it in another socket with an adapter and still the same behavior. One thing that I need to note that it's only with tubes from one manufacturer. The tester shows me that Tubes is at minimum good, but emissions on the other one are at 100%. For all other tubes if mutual conductance goes down emissions always go down - but not for these tubes. Very strange. And in the amp they behave like champions O_o
Another interesting point, I used in my amp for a couple of days - it was measuring 1.1 millimhos where rejection is 1.2 - worked beautifully. Now I tested it on Hickok and it shows 2.5!!! Every time. Is it possible that it's burning in?????
What brand of tubes are these? It's important to know, because I probably have the explanation - if I know what tubes they are.
These are Ei 12ax7 tubes.
The Ei quality was pretty awful towards the end of production - but I don't know whether that is what you are seeing. You may have tubes with cathode poisoning, and they need to "wake up" (by getting rid of the contaminants on the cathode surface) before they operate normally.
I'd recommend you run them for a few hours before testing them. And remember - the ultimate test of a tube is whether it works properly in a circuit!!
Thank you for all your help. I will continue playing around with the tubes to see if I can detect a pattern :) So far although they show below minimum on Hickok I'm loving them in my amp! Very surprised by the quality of sound.
...Although it should be a gradual phenomenon, not intermittent. I've experienced this with the 12AX7LPS. Another possibility is that the tester is oscillating under certain conditions. This is a lot more likely with hi gm tubes like 6550 and almost impossible with something like a 12AX7. One check is to put your hand over the tube while under test. If it's oscillating, the reading will jump around a lot while you do this. Hickok got around this tendency by using ferrite beads on all socket leads on their later testers. Another point to keep in mind is that a lot of Hickok testers way overdrive hi gain tubes like the X7 while under test. Only the best versions use an appropriate 0.25 or 0.5VAC as the test signal.
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