FYI: These tubes are measured in autobias mode according the manufacturer data sheet.
More information you find at the end of this describtion
1 x tube E88CC 6922 Telefunken
Free of other defects such as grid current, vacuum issues, or noise
Gm/µmhos : 13500 + 13000 (100% = 12500 ±2500 )
Produced by Telefunken ULM/Donau plant
Measuring
device used: RoeTestV11.
Measurement mode: Autobias as specified
by the manufacturer.
In autobias mode the tube is measured with a
constant anode current. This corresponds to the application in the
device.
Note: Most tubes offered on ebay are tested with a fixed
grid bias voltage. Such a measurement contains a general system
error. The desired result in the application is therefore purely
random.