Been playing with the SSE amplifier and I am noticing a 20% difference between the dual triodes on many of my 12AT7's especially the newer made ones. Bought a pair of Psvane 12AT'7's to play with and one was satisfactory and the other unusable unless one want half the power on one channel. I was measuring the voltage drop across the tubes to see the differences then testing to see what the power output at clipping was and that is what I found. I have a couple I bought used from Tube Depot that have a big difference between the two triodes as well. Not as much as the new Psvane but a significant difference. Chances are one will not notice this in a tube that is not too extreme but it is there. I knew there was a normal 20% difference between any production run of a tube but did not realize this applies to dual triodes in one envelope as well. One could bias the two sides differently to equalize the outputs but then it means if one changes the pre tube it would have to be done again which is not a big problem for a diy'er but not acceptable for a retail amp. What I am doing is purchasing a number of 12AT7's and picking the one best matched to use in my amplifier. I have noticed that the Gold Lion gold pin tube advertises balanced sections but at a premium price. Has anyone else noticed this?
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In circuit measuring the voltage drop of the tube measuring the cathode to plate voltages. I am really curious if this is the case with the many other 12A*** dual triode tubes, 20% tolerance. I expect it is what manufacturers call normal 20% tolerance, the imbalance in a dual triode. The really awful Psvane I just bought cost like $18, not worth the time, trouble and expense to send it back asking for a refund with the cost of shipping these days. What I have found tells me if you want the best out of your diy amplifier try finding a matched dual triode for best performance.
I do not have a tube tester but I do have access to one but I have found in circuit is the best test for any component.
Depends on the tube what K-P voltages, the Psanve measured like 260V one side and 210 the other. The current is constant in the SSE, less than 10ma, .9 something. The good Psavne measured 220v and 220v K-P.
Bought a GE 12AT7 off Ebay and it measured with close matched sides and decreased the harmonic distortion figures at 1khz 1 watt more than half. Figures are now .27% THD+N whereas with the best Psvane it measured .92% at same level. It appears that the Chinese tubes still have quality control issues. That and reducing the noise in their tubes. At least in the 12AT7 ones.