A typical 12AX7 data sheet can be found here.
Keep in mind than many folks who make tubes copy some of the data off these sheets and put the specs into their own data sheets. They don't make tubes that come close.
In the past during the six plus years I was at Groove Tubes, their CEO Aspen Pittman let me publish my test results and send the results to the tube makers. We also produced data sheets based on measured results rather than on hopes and wishes for all the major manufacturers. Data was also part of the hard copy deluxe edition of The Tube Amp Book. JJ was the only manufacturer at the time (2002-2008) that would act upon what was reported and make changes. They also kept in touch and followed up. New Sensor / Sovtek could care less. If somebody sends a copy of this to them I would be more than happy to explain how everything was done and give them all my test procedures. Based on past experience I don't think I have to wait by the phone.
As a side note, Aspen Pittman made countless trips to the factories that were producing his "NVM" tubes and I had monthly meetings at the GT factory on the GT exclusive tube line. Aspen went through hell on the 12AX7M and 6CA7 trying to make them right. The first three runs of the 12AX7M were the best 12AX7 tubes I had ever tested. Unfortunately the factory could not keep up the quality or consistency.
|DATE||TUBE||B+ volts||BIAS volts||mA actual||TC (gm) actual||gp||Plate Resist||Gain||Comments|
|3/23/2013||Genalex Gold Lion||250||2||1.6||2420||0.0285||35.1||84.91||A Sovtek 12AX7LPS by another name|
|B759 Reissue||0.8||1190||0.0180||55.6||66.11||A “Mullard” reissue by Sovtek by another|
|1.2||1550||0.0170||58.8||91.18||This is the one tube that came close|
|Averages||1.2||1573||53.2||81.69||<- Output averages|
|96.7%||98.3%||81.7%||<- % of standard spec|
|High TC||2420||151.25%||12AX7 Design Spec|
|Low TC||1190||74.38%||1.2mA current output|
|QA tolerance TC||76.9%||1600 TC|
|High mA %||2.1||175.0%||62.5K plate resistance|
|Low mA %||0.8||66.67%|
|QA tolerance mA||108.3%|
|QA tolerance gain||25.1%|