I was asked a question on another forum and grabbed some of my reply to post it here. If you want to push the output section as hard as possible the JJ 803S long plates are currently the highest gain 12AX7 tubes made at the moment today. Typically their gain is over 90 and most other 12AX7s today are 80-85. Five points of gain might not sound like much but it is quite a difference. Here are the actual gain numbers in circuit that the last batch two weeks ago showed in testing which was even stronger than the previous run from JJ: 98.2 99.6 94.4 98.5 96.1 101.7 95.8 100.6 100.0 101.9 98.9 99.5 98.5 102.5 97.8 102.2 94.0 93.1 98.5 100.4 92.8 95.6 96.1 99.4 98.1 100.6 97.6 94.8 100.5 94.8 95.2 92.3 96.5 95.9 96.8 97.8 92.9 98.2 96.2 101.9 100.6 99.5 97.4 100.0 98.5 102.5 94.3 97.0 Pretty spectacular.
As I understand it the 12AX7 is a 100 mu tube though most of todays 12AX7's dont live up to thier design specs as far as gain concerned.If Im correct then these JJ's actually do pretty much achieve thier design specs for gain. Bob
You are right on the money. In the past I have posted a lot of tube test data in this forum on many makers tubes. I usually publish a much more detailed report but for this one only published the true gain in circuit which is different than plate current, plate resistance or transconductance. Unless PR and TC are in a proper relationship the true gain will not be proper. Most tubes today have plate resistance that is too low. This makes the transconductance read very high on common testers and test as a great tube when in fact it is not all that great at all. Low plate resistance generally shows up as a tube with low gain which is common today.
There still is nothing made now that sounds as good as the old stuff. Numbers mean nothing to me other then output, it could be poor tone that's just louder, big deal. Sorry to be sour grapes but they still haven't got it figured out.
They were one of my favorite new production tubes before I went old stock. They seemed to have a rich sounding break up/distortion with plenty of highs but not harsh-quite different from the JJecc83s. I did have two in a row die after only a few hours on them though.Bob
This tube seems like a great one to experiment with. If selected carefully, would this long plate variety stand up to the rigors of a 2-channel 50W, 112 combo? Best placement in the chain...phase inverter?
I would be very interested in seeing this type of Data on JJ's ECC802S long plate as well. Maybe even the ECC81 Since the most recent EH12AY7's are only good for pellet gun practice, It would be nice to see something similar in gain.
