[Boatanchors] testing 0A2 tubes?

[Robert R. Kerr]

Eugene,
I'm not sure what sort of test your tube tester is set up to perform on 
gas regulator tubes.  A "gas" leakage current test for conventional 
tubes is not appropriate, as gas regulators have a different sort of gas 
introduced intentionally.

If you have a meter that shows current through the tube, that is of 
interest.   You want to know the minimum anode-to-cathode voltage 
required to ignite the gas (ionization) and, once ionized, the minimum 
current through the tube required to keep it ionized.  While the gas is 
ionized, the voltage across the tube should remain fairly constant near 
the rated regulation voltage for the tube.  The 0A2 should ignite once 
the anode to cathode voltage reaches 165V and regulate at near 150V.  It 
should maintain regulation over the range of 3 to 30 mA, mimimum.

Your tube tester should have a resistor in series with the tube (there 
is probably a selector switch for the resistance value) to establish a 
suitable current once the tube is ignited. 

However, if the series resistance is too high, it can cause the tube to 
cycle on and off rapidly, i.e.:  Starting with 1) a voltage source 
hooked up from the cathode to the anode of the tube with a resistor in 
series then 2) increase the voltage until 165V is reached then 3) the 
tube ignites and the voltage across the tube will drop to 150V.  4) The 
resulting 15V voltage drop across the series resistor causes a current 
(15V/ series resistance) to flow around the circuit (the series 
resistance of the ignited tube is very low and is ignored here).  
However, 5) if the flowing current is less than the sustaining current 
for the gas ionization, the ionization will cease rapidly; the glow will 
go out, and the current will cease, at which point we're back to step 3) 
above and everything starts all over again: on/off, on/off......

Once in the above condition, you should be able to get a sustained gas 
discharge on the tube tester by either increasing the voltage source 
voltage or decreasing the series resistance

When gas regulators go bad, either some of the gas has leaked through 
the envelope, or some air has leaked in, or some of the cathode coating 
has evaporated and gotten into the gas mixture.  The results are usually 
a significant increase in the minimum current required to sustain the 
gas discharge, or poor voltage regulation for currents near the maximum 
range or both.

Bob
WB4TGG


Eugene Hertz wrote:
> Hello all, while trying to troubleshoot a possible regulation problem in a transmitter, I decided to test my 0A2 tube in my tester which is an I-177-B military thingy.  Apparently, the test it can do is limited and they caution that this is only a partial test.  However, the results are bizzare! So I thought my tube was bad because it tested around 500 (on the scale, however I dont think its micromhos that its reading for 0A2 tubes) but the needle would bounce around terribly while pressing the "GAS 1" button. With each purple flash in the tube, the needle jumped sometimes to zero. I even let the gas1 test stay on for 1 minute or so in case there was warm up involved. 
>
> So I decided to buy some more tubes. I bought a bunch on ebay from a seller who has VG feedback and said the tubes were used but tested strong.  However on my tester, one was nearly a dud (scoring less than 50 on the scale) others seemed very weak and "bouncy" while only 2 were "strong >500" and stable.
>
> What does it all mean? Is stability of the needle something that is good or indifferent? The manual says >200 is good, but is 1000 better than 200 or is a tube like this either good or bad with no in between?
>
> Is there a better way to test these things? Should I throw out this tube tester and get something "better?"
>
> thanks
> Eugene
>
>
>
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