[Amps] Photos posted of high voltage test setup of a YC-176

LB3HC rezycle.bin at gmail.com
Fri Oct 21 12:54:04 PDT 2011

Hi George.

I didn't test breakdown between G-C so far. In a grounded grid setup with a tube like this, my understanding is that an A-G arc is the most likely. The grid is a circular cage surrounding the cathode (reference: internal pictures of the YC-159 at http://gs35b.com/yc156/ ). The grid potential will stay very close to B-. I assume therefore that since the potential between G-C will be quite low, the risk for an arc there is low.  (Provided the low ohm clamping resistor from chassis to B- is OK). I may of course be wrong.

I have not yet found many references that state that one should do a hipot test from G to C. In studying the Eimac datasheet for the YC-156 http://www.g8wrb.org/data/Eimac/YC156.pdf  (YC-156 is same tube as YC-179), I see on page 3 that the maximum G to C peak potential should be 425 volts.  This may indicate that one should be careful with applying too high voltages from G to C. If you have more specific information about what voltage the G-C path should hipot test without appreciable leakage current for a good tube, I would be interested in receiving this information.

I agree with your comments regarding unknown heater and grid condition. That I will have to test and cross my fingers.

An alternative may be to check the interelectrode capacitances. That would probably give an indication of misaligned elements inside the tube.


>>  I assume I have a good tube when it shows that low leakage at 16KV (DC). Any opinions on that?
> That's assuming a bit too much.  I'd say it means you have a good VACUUM, but:
> the filament might be open, or have low emission
> the grid might be damaged from a previous overcurrent event(s).
> the grid might be shorted to the filament.
> But, so far, it looks like you might have a good tube.
> The next thing I'd do is test interelectrode leakage between the other elements.  
> Then, I'd see if the filament works, i.e. draws the correct current at the correct 
> voltage.  If you heat the filament for more than just a few seconds, be sure to provide 
> some cooling air. 
> Good luck es 73,
> George T Daughters, K6GT
> CU in the California QSO Party (CQP)
> October 6-7, 2012

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