Pics of left channel, 1st grid, 2nd anode & 3rd output.
If you didnt I suggest you calibrate your tools. Your measurments differ around 5000 percents.
The cyfers in black represent a bias of (10+11.4)/2 = 10.7 volt... Also pic with schematic with measurements.
The red ones give (9+10.4)/2 = 9.7 volt.
So, you're one volt of bias low with this tube.
As a result 16mA of current is standing, instead of 5mA.
Can you replace the 10 ohm resistor?
Attached pics: DC measurements & current + resistors pic (it's a little bit complicated to replace)
With the new DC left channel still doesn't amplifies.
Check for oscillation. DN2540 could be oscillating too.
Thanks Iko, how can check? Is when I see more than one sinewave moving on the scope?
N.B. Are you sure DN2540 is sharing both channels.
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