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

[LB3HC]

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.

73
LB3HC


>>  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