Tubes Asylum

Posted by Chris Haedt (A) on July 07, 2003 at 15:04:30

In Reply to: Re: Tube tester rating ambiguity posted by jstrm on July 07, 2003 at 13:37:48:

OK--perhaps a better wording would have been. . not all tube testers in use today have been properly serviced and calibrated.

About the TV7 thing. These are excellent testers--but (a) the readings they give are in numerical units that can be converted to micromhos, and this conversion is usually stated to be "theoretical", and (b) I am not sure why a reading from a TV7 SHOULD agree with a 539C. The reason is the transformer sag correction that is made when testing with a 539C. In this tester the AC line input and the bias are reset to proper values WITH plate current flowing. That is why the 539C has that locking gM button. This is not possible when testing with a TV7. In the TV7, the voltages all sag when the test button is depressed, and this is adjusted for in the data. If you made a 6L6 test the same on both the TV7 and 539C testers, I would think that lower plate current tubes would test too high on the TV7. I'd like to know the details of this.