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In the Forum: Audio For Dummies ™
In the Thread: Get, or made up a tube tester, it’s necessary
Post Subject: What the tube trace might show in the real world?Posted by Romy the Cat on: 1/8/2007

 hagtech wrote:
I have not tried this tube yet.  It might push the limits of the tester.  The 6.3V heater current supply is nominally rated at 5 amps.  It might be ok to push it to 6.6 amps.  I have to think about this, make sure there is some headroom in the transformer core.  Easiest thing would be to fire up a tube and see what happens.  Send me one and I can trace it for you (of course I will return it).

I do not think that heater supply is a problem. The 6C33C has 6.5A at 6.3V

but I usually very liberal with abusing tube testers. My Hickok TV2 is rated at 6.3V at 3A if I’m not mistaken but after a few out of hearing a half of 6C33C it has absolutely cool transformer. In fact when I was making the Hickok be able to handle the 6C33C I had power resistors smoke (I replaced all of them with more powerful) but I never had problem with filaments. In the worst case it always possible to feed the tube heaters form externals transformer… My biggest question is: will a trace be able to tell me the “state of the mind” of a given tube.  If you would to burn you time like I might send you two 6C33C – a new one and the burned out (you would not need to return it) and it would be interesting it the traces would be interpretable. Unquestionably to have a trace for the very given tube is “nice to have” but does it have any practical meaning for the semi-armature, purely “usability” tasks that I need to resolve with this tube?

 hagtech wrote:
The VacuTrace does something the others don't.  It measures output conductance.  Or one over plate resistance.  This value will give you a comparison on loading.  A tube with higher plate resistance will obviously have lower output gain into a load.  So you are correct, there is more involved than just transconductance.

Actually this is very cool feature for my low frequency channel in Super Melquiades. A change current in plate changes impedance of the plate and with consequentially affect the loading. In the past it was kind of balance between how hard you can drive the tube with currant and where the transformer core stop to handle it. With Super Milq LF transformer, gaped at 450mA I can go as high as I wish but staring at some level the sound stop to be changing. I wonder it that “level” would be different for different tubes and will another 6C33C’s plate have different impedance at given current, I am sure it will. Well, it is possible to circulate by “other ways” theoretically….

 hagtech wrote:
So you are correct, there is more involved than just transconductance.

BTW, I was in past contemplating to add to my tube test the “real gain” mode. I was thinking to rectify and filter plate current and feeding the greed with 1000Hz for a simple generator to measure AC on the loaded tube’s plate… It world give me the “no BS gain”… Frankly speaking it is the only one of the two real world parameters that I care (cathode emission, relive to what it was at the very same tube when it was new is the second one)


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