Mullard Long Plate 12AX7 ECC83 tube. Code B7B, Britain. AT1000 87/93% gm.

The other code looks like mC1.  

Made in GT. Britain. 

 

Before testing the heater was on for at least 2 minutes and plate voltage was applied for at least on minute. 

Also checked for shorts, noise, and microphonics.

The AT1000 was set to Fixed Bias mode.

It tested on a Amplitrex AT1000.  One of this tester's attributes is detecting gas.  Any low level gas the AT1000 detects, it is likely other testers will not measure any gas at all.

The Transconductance spec for a new tube is 1600 mhos at 250 plate volts.  

Amplitrex AT1000 results. 

Tube Emissions % GM % mhos H-K leakage ua Gas mA

12AX7 ECC83 91/91 87/93 1400/1500 0/0 .0/.0

The gas value above is well within the good range.  The tester manual says for signal tubes the gas ma should be less than 1ma.

These are well below 1ma.

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