Rerurn to Romy the Cat's Site


In the Forum: Audio For Dummies ™
In the Thread: Get, or made up a tube tester, it’s necessary
Post Subject: the sound of one trace loopingPosted by hagtech on: 1/26/2007
It's hard to predict how the anomaly will sound.  Sort of like a dynamic bias shift in the tube.  That's why I think IMD.  The shift moves around at LF rates, so the HF reproduction can fall on any number of load lines (within loop area).

Or it may not show up at all.  The loops occur only in one region of the plot.  In a typical amplifier, the load line might be passing through zero here, keeping amplifier operation away from the faulty area.  Maybe the loop happens everywhere, but is only visible at high current, high grid voltage.

Sure, send more tubes.  I also think this one 'faulty' tube is ripe for another test.  As you mentioned, some of your amplifier stages only use 1 of 2 sections.  You should be able to hear a difference between sections in this one tube. 

... output two independent traces ... at the same time?


It can do two tubes at once.  The traces are alternately swept so they appear to be overlayed on the scope.  One of them gets 'dotted' by modulating the Z-axis input of scope.  This function is only useful on smaller tubes, as it depends on total cutoff at -70V grid.  Is this what you asked?  Here is example of preamp tube, both sections swept together in real time.



jh

Rerurn to Romy the Cat's Site