What do these tube test results mean please?

[esperowl]

Hi, this one is for any tube afficionados out there. I'm need two ECC82 / 12AU7 tubes and I've found a guy selling three vintage tubes. Being very new to the world of valves, the tests results mean absolutely nothing to me and from what I've read in the last day or so, some sellers will report results for particular aspects but don't give an overall picture of the health of a tube, or test tubes on cheap machines. What aspects should I be looking for?

Anyway here are the results -

Tested on a Hickok 6000A Min= 2200/2200

3250/2900

3000/2800

3000/2850

Thanks in advance.

[Riislingen]

Hi Chang,

The results cannot stand alone of course, but is a good indicator.

The Hickock numbers are the tester equipments reference numbers, indicating the threshold for a "good" tube.

The numbers usually refers to the emmission of the the two anodes in the tube. So for the tests in question they all perform substantially above "good" and have pretty balanced sections as well - they are per se NOS.

Add to that test for gas/leakage and microphony. Most sellers would state this alongside the test results.

[Jazid]

Interpreting results of 50+year old testers is rather problematic due to differing testing standards and more importantly drift of cmponents in the tester. Bear in mind it ihas been near impossible to get these things calibrated since the 1980s.. On the surface these appear good, I would still suggest that if they are not significantly cheaper than Billington/Chelmer/Watford valves you go there where quality is more assured.

[Riislingen]

Interpreting results of 50+year old testers is rather problematic due to differing testing standards and more importantly drift of cmponents in the tester. Bear in mind it ihas been near impossible to get these things calibrated since the 1980s.. On the surface these appear good, I would still suggest that if they are not significantly cheaper than Billington/Chelmer/Watford valves you go there where quality is more assured.


Excellent points ! :cool:

[esperowl]

Thankyou both. I think the seller is wrong when he states that the minimum conductance value = 2200 (another seller informed me that this value is the average). A further concern is that the values seem very high (too good to be true?) and that the valves were not tested for shorts (gas leakage shouldn't be a problem as the valves in question are 12AU7's).
I saw them on ebay and even a valve novice like myself can soon conclude that ebay is a minefield when it comes to buying used tubes.
I'll stick with more established outlets (Billington / Chelmer / Watford - thanks for the tip).

[DaveK]

You might find it interesting to take a look here: -

http://www.rock-grotto.co.uk/x-ccessories.html (scroll down the page a bit).

Mike Grierson who owns the show is an absolute wiz with valves and a fair guy to deal with but can sometimes take his time to respond. Anything he states about test results or anything else regarding his valves can be relied on.
Dave.

[Riislingen]

Chang, Sent you a PM

[Jazid]

Thankyou both. I think the seller is wrong when he states that the minimum conductance value = 2200 (another seller informed me that this value is the average). A further concern is that the values seem very high (too good to be true?) and that the valves were not tested for shorts (gas leakage shouldn't be a problem as the valves in question are 12AU7's).
I saw them on ebay and even a valve novice like myself can soon conclude that ebay is a minefield when it comes to buying used tubes.
I'll stick with more established outlets (Billington / Chelmer / Watford - thanks for the tip).

2200 is the minimum result that a new tube would be allowed to pass through quality control with. It is usual for tubes to exceed by the amount given, it is unfortunately in my experience equally usual for sellers to give bogus figures, or figures that come from their testers with the kind of 'no two testers agree therefore mine is right' kind of caveat, not that I am in the position to suggest this is the case here of course. The problem is more on balance between sections - I rarely see perfectly balanced tubes from any supplier. These being rated as showing an ok match I'd suggest the seller is being straight, but unless you have a tester you won't know. More importantly gas is ALWAYS a possibility in any NOS valve, and should be tested along with cathode/heater insulation as a matter of course. Valves with gas often show a period of high emmissions due to extra current caused by the ionization of the gas molecules by the electrons from the cathode. This also can cause the bluey halo around the anode that can be seen in failing valves.

[DaveK]

Sent you a PM

Who, me? Nothing received yet (20.30 hrs.)
Dave

[Riislingen]

Who, me? Nothing received yet (20.30 hrs.)
Dave


Sorry for Chang..edited above accordingly. :doh: