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Old 25th March 2013, 04:57 PM   #1
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Default ECC81 mu-follower problem

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?
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Old 25th March 2013, 05:01 PM   #2
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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?

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Old 25th March 2013, 05:10 PM   #3
kevinkr is offline kevinkr  United States
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There has got to be a wiring or component value error.. There should at least 3mA flowing through that resistor.
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Old 25th March 2013, 05:12 PM   #4
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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?

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Old 25th March 2013, 05:16 PM   #5
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Quote:
Originally Posted by Rundmaus View Post
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

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Old 25th March 2013, 05:17 PM   #6
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Quote:
Originally Posted by Rundmaus View Post
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
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Old 25th March 2013, 05:17 PM   #7
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Filaments wired for 12.6 operation with 6.3V applied?
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Old 25th March 2013, 05:19 PM   #8
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Quote:
Originally Posted by Rundmaus View Post
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
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Old 25th March 2013, 05:20 PM   #9
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Quote:
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Filaments wired for 12.6 operation with 6.3V applied?
6.3V
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Old 25th March 2013, 05:27 PM   #10
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Enclosed circuit used
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