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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: and I only wanted to gripePosted by hagtech on: 1/8/2007

 cat wrote:
Will your tracer be able to pump 250-300mA at 230V? Will it be able to supple up to 100-110V of bias?

Not quite.  I designed it for preamp tubes.  But then I realized I could push it to cover a lot of the more popular output tubes such as EL34, 6550, and even 300B.  The VacuTrace is limited in how hard it can drive a power tube.  It'll deliver 200mA to plate at up to 400V  (really about 380V under load), and only -70V of bias.  This does NOT cover the full range of the bigger tubes.  It will, however, give you a pretty good idea of the condition of the tube and often covers the operating point.  I show this example of a 300B. 

The red overlay is actual photo of VacuTrace output.  It is indeed limited, but does cover a big swath of operating region.  As far as hard-wiring adapter cards, that is pretty straightforward as I sell "blank" ones. 

Russian 6C33C that have absolutely random quality

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 need to use one of those commentary scopes with memory

You definately need at least a cheap analog scope, with XY capability.  As for measuring tubes over time, I hadn't thought of that.  Do you think the curves are shifting?  Sure, a tube warms up.  To measure degradation over some time, I think the easy way is to just take two photos.  Maybe you know somebody with a camera?  Ar ar.  One before and one after.  Or you can take spot measurements of current, transconductance, and plate resistance and some specified operating point.  The VacuTrace is limited to withing its range.  If you try to drive it too hard the internal amplifiers protect themselves and go into a "chirping" mode. 

It does not work to test microphonics on this machine.  Nothing shows up on the scope. 

reference current thought the grid, measuring the actual gain

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.


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