14-08-2020, 05:53 PM
OK, the snooker has finished, smashing match, shame there can't be a draw.
In fairness to Alistair, he was on the ball. Not disconnected but..................
The cathode circuit with the negative feedback is unusual, the cathode current is via the secondary of the output transformer. So the output valve is drawing about the correct current but it is all down to the screen, the section b of the output transformer is completely open, the anode has zero volts.
What amazed me is the lack of distortion, if you could accept the low, but sufficient to listen to, volume you could accept that it was just a low emission valve.
The EL84 showed no distress, and with a new transformer without the hum cancelling winding, the valve is fine, the volume is huge, the sound is clear.
I would not have thought that so much current could pass by the screen without it getting red hot.
Hope you enjoyed the brain exercise. Thanks for taking part.
Sam.
In fairness to Alistair, he was on the ball. Not disconnected but..................
The cathode circuit with the negative feedback is unusual, the cathode current is via the secondary of the output transformer. So the output valve is drawing about the correct current but it is all down to the screen, the section b of the output transformer is completely open, the anode has zero volts.
What amazed me is the lack of distortion, if you could accept the low, but sufficient to listen to, volume you could accept that it was just a low emission valve.
The EL84 showed no distress, and with a new transformer without the hum cancelling winding, the valve is fine, the volume is huge, the sound is clear.
I would not have thought that so much current could pass by the screen without it getting red hot.
Hope you enjoyed the brain exercise. Thanks for taking part.
Sam.
Boater Sam.
