Question for 12AX7 tube experts

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stratjacket

stratjacket

Well-known member
Ordered some new preamp tubes and it's been a while. I can't remember what the numbers are on the box. For example, on the 12AX7 tubes I have:
95.3 and 96.1
2110 and 2070
written on there.

I believe the 95 and 96 numbers are gain measures?
Have no idea what the 2110 and 2070 numbers are and google search did not help much.

The site I bought from says this about their testing:
"Our preamp tubes are tested using power-regulated Maxi-Preamp testers for Mu (gain) and Gm (general mutual transconductance) at proper operating voltages. Preamp tubes are also screened for all other appropriate parameters such as shorts."

I ordered a matching set of 5 preamp tubes and they all have similar numbers. Wondering if the highest or lowest numbers would typically go into V1 for example.

Any help please?
 
Smash said:
The only thing that i know about youtube is that beta faces help get clicks
Click to expand...
Ha, but what if they have numbers instead of faces? But point taken...will edit the title...
 
The other numbers are transconductance (Gm).

Transconductance is a measurement of the ability of a tube to transmit current. It is the product of the output current in amps divided by the input voltage at the control grid. Transconductance is significant in that it shows us the difference in current capability that is generated by variations in plate impedance between tubes.
 
psychodave said:
The other numbers are transconductance (Gm).

Transconductance is a measurement of the ability of a tube to transmit current. It is the product of the output current in amps divided by the input voltage at the control grid. Transconductance is significant in that it shows us the difference in current capability that is generated by variations in plate impedance between tubes.
Click to expand...
Awesome, thank you.
Would higher numbers be "better" then?
 
Transconductance is more commonly called Siemens. It used to be called mhos which is ohms spelled backwards. The larger the value, the greater the sensitivity of grid voltage to electron conduction from cathode to plate.
 
The transconductance value is pretty meaningless in tube guitar amps, unless there is a big difference between the sides.. or it if very low… below 1000.

The Mu (gain number) is more important. I like to put the higher rated tubes in V1 to boost the gain. Some tubes will have a Mu rating over 100 per side. I’ve got a few with 140/140 per side.
 
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Wizard of Ozz said:
The transconductance value is pretty meaningless in tube guitar amps, unless there is a big difference between the sides.. or it if very low… below 1000.

The Mu (gain number) is more important. I like to put the higher rated tubes in V1 to boost the gain. Some tubes will have a Mu rating over 100 per side. I’ve got a few with 104/104 per side.
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I have a few that are 130 each side. They actually sound great.

The TC over 1000 has meaning. I have a bunch of long plate Ei that test over 100 Mu, but are 1200-1400 in TC. Those tubes in the PI really push the signal to the power tubes.

This is why I have tube testers, I like to know what is in my amp so I can replicate it.
 
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