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-   -   ECC81 mu-follower problem (http://www.diyaudio.com/forums/tubes-valves/232779-ecc81-mu-follower-problem.html)

merlin el mago 25th March 2013 05:57 PM

ECC81 mu-follower problem
 
1 Attachment(s)
I have noise in both channels, I do the measurements and the voltage between the two tubes in place of 85V I have 175V after this measurment I tested the heater elevataion and voltage is ok 76V, can be the two tubes are damaged?

Rundmaus 25th March 2013 06:01 PM

Your measurement would mean there is a voltage drop of only 8.7V across the 33k resistor, meaning a plate current in the lower triode of approx 0.2mA. Is that the intended operating point?

Rundmaus

kevinkr 25th March 2013 06:10 PM

There has got to be a wiring or component value error.. There should at least 3mA flowing through that resistor.

Rundmaus 25th March 2013 06:12 PM

Please measure the voltage drop across the 470R cathode resistor to confirm the plate current problem in the lower triode.

Does the heater of the lower valve light up?

Rundmaus

merlin el mago 25th March 2013 06:16 PM

Quote:

Originally Posted by Rundmaus (Post 3426827)
Please measure the voltage drop across the 470R cathode resistor to confirm the plate current problem in the lower triode.

Does the heater of the lower valve light up?

Rundmaus

I have a red LED and measures both channels 1,8V

the 4 heaters have light up

merlin el mago 25th March 2013 06:17 PM

Quote:

Originally Posted by Rundmaus (Post 3426814)
Your measurement would mean there is a voltage drop of only 8.7V across the 33k resistor, meaning a plate current in the lower triode of approx 0.2mA. Is that the intended operating point?

Rundmaus

I measures 175V instead of 85V

kevinkr 25th March 2013 06:17 PM

Filaments wired for 12.6 operation with 6.3V applied?

merlin el mago 25th March 2013 06:19 PM

Quote:

Originally Posted by Rundmaus (Post 3426814)
Your measurement would mean there is a voltage drop of only 8.7V across the 33k resistor, meaning a plate current in the lower triode of approx 0.2mA. Is that the intended operating point?

Rundmaus

No, 33K resistor have to drop from 183,7V to 85V not 175V

merlin el mago 25th March 2013 06:20 PM

Quote:

Originally Posted by kevinkr (Post 3426840)
Filaments wired for 12.6 operation with 6.3V applied?

6.3V

merlin el mago 25th March 2013 06:27 PM

1 Attachment(s)
Enclosed circuit used


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