JJ Electronic makes 4 different dual triode tubes in the ECC83 (12AX7) vacuum tubes family. Each tube has a unique structure, gain rating and sound. There is variation between each of these tubes, as well as variation within each tube family.
When installed in a tube amplifier circuit it becomes really hard to tell what a tube is doing in isolation. As the tube is changed, the circuit reacts to the change. Looking at the amp output power or simply listening to the perceived loudness doesn’t really tell you where the change came from.
I decided that the best way to see what was going on, was to directly measure the voltage amplification of the tube. JJ has 3 gain levels in their ECC83/12AX7 tube line. The highest, or standard level, comes from the ECC803S and the ECC83S. These are direct replacements for a 12AX7. The next gain level comes in the form of the newly released ECC83 MG. This tube is claimed to have gain below a standard ECC83 but higher than the JJ 5751. The 5751 is an ECC83 substitute with lower noise and gain.
When I listened to each of these tubes as a preamp in guitar tube amplifiers, it was very hard to say if the loudness changed in accordance with JJ’s claims. Measuring directly from an isolated triode section seemed to be the best way.
I inserted a 200 millivolt signal into one of the triodes and measured the output voltage. This is what I found.
|TUBE||INPUT VOLTAGE||OUTPUT VOLTAGE|
|ECC803 S||.200 volts||12.23 volts|
|ECC83 S||.200 volts||12.33 volts|
|ECC83 MG||.200 volts||11.76 volts|
|5751||.200 volts||7.94 volts|
The measured results reflect exactly what JJ claims about the output of their tubes. The ECC803-S and ECC83-S are virtually identical. A slight gain reduction is seen in the ECC83MG, while the gain reduction with the 5751 is quite noticeable.
The real question is will I hear it? Keep in mind that gain aside, each tube has a different plate design and different internal resistances and capacitances. That’s where much of the difference is to be found.