Just to chime in as requested. All test results are bull**** unless you know what the point at which the tube tester takes measurement.
I will zoom out a bit and talk about measurements in general and average 100% and so on.
The general point for measuring a 6DJ8/6922 is Heater voltage(or filament voltage) Vf(Vh) = 6.3V (sometimes marked as Uh or Uf) , Plate voltage (Anode voltage) Va(Vp) or Ua(Up)=90V, Grid voltage = Vg or Ug = -1.2V for E88CC and -1.3V for ECC88
So now that we have this point tuple (Vf, Va, Vg) we can rummage through the specifications over here
http://www.mif.pg.gda.pl/homepages/frank/vs.html a search of "CV2492" shows our equivalent E88CC specifications.
There are not any specific BRIMAR specs there but we can use the Philips ones to give us a rough estimate. The Brimar pair linked ->
http://www.ebay.com/itm/222591787203 is from the late 60s so let's use the Philips (>1965) spec. On Page 10 of that PDF we can see averaged characteristics at Va = 90V, Vf = 6.3V . Here we can see that the 15mA vertical line is hitting the -Vg curve at ~ 1.2V and the S(S = Siemens = Gm = transconductance = slope) curve at around 12.5 mA/V and the Mu (Voltage gain) curve at 33. So there you have it , when the average Ia = 15mA, you have Va=90V, Gm = 12.5 mA/V, Vg = -1.2V and Mu = 33.
Using the specs in the way described you can derive averaged 100% for any tube characteristic at different points of measurement (Vf, Va, Vg). Now the tube sellers should in general provide these points of measurements they used in their listings however sometimes they do not for several reasons:
1) They outright lie (motherfrakers) because they know most people are looking for that phat juicy number of Ia = 15 mA (100%!!11!!oneneEleven!!), but without the point being specified it's meaningless! Why? Well let's take a look at that page in the specs as before the left chart is at Va=150V, now let's check our lovely Ia=15mA current characteristic, we work our way up the vertical line again and we see that Vg is between -3 and -3.1, but if we leave Vg unchanged (at -1.2V from before) and with so much juice going into the tube (150V) the current will go crazy high (more than 30mA maybe more for a healthy tube) . However... let's say that our tube still measures at 150V , -1.2V , Ia = 15mA this means this tube is far far far from the average 100% and that's where they get ya
2) Their tube tester is old and gimmicky, hard to use, hard to explain, hard to understand, you have some cards that say "ROTATE SELECTOR X to VALUE Y for TESTING TUBE Z", and "FOR TUBE Z 100% GM is 6500Mhmos". So this seems to be the case with your listing. If you take a look at here
http://www.saegerradio.com/downloads/Consolidated Test Data For Hickok Model 533A-600A-605A Tube Testers V2.5.pdf you can see that for E88CC with the tester Hickok 533A you need to use the following settings:
Selectors: EV-7608-0 EV-2103-0
Bias: 27
Eng (English): 90
Press (Which button to use to test): P4
Gm scale = 6500 mhmos ( so you expect the 100%)
If we read the manual for that tester you can see that the selectors are using to configure what voltage is put on what pin of the tube.
There's not much I saw about Bias and English but we can assume that Bias 27 is equal to Vg=-2.7 V, and English Va= 90V on the plate (could be wrong but I can't find an explanation to these values and they resemble Grid Voltage and Plate voltage so much and the math kinda checks out
) . So at the time this tester was made we don't know what the charts were, perhaps at 90V/-1.2V the expected transconductance was 15 mA/V. But either way if we look at the values of Gm at that point we can see that when Vg = -2.7 V and Va=90V , 100% averaged Gm ~= 4.5 mA/V (4500 mhmos). So bottom line the tubes in question should be great as they measure above that. And even if 100% was 6.5mA/V the difference is negligible.
Cheers
reading some forums other than Headfi, many people consider these to be on par or better than the WE 396a's. And that price! Maybe this tube rolling hobby won't kill my wallet after all. There were are couple other pairs for sale
