6N2P/6Н2П low plate current increases noise? - diyAudio
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Old 27th January 2013, 08:20 AM   #1
FLT is offline FLT
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Default 6N2P/6Н2П low plate current increases noise?

Hello everybody,

I am using the 6N2P as diff-amp-phase-splitter input of my current project.
Plate current per system is 0.5mA, taken from "http://www.rutubes.com/index.php?show_aux_page=6"
(How to use 6N1P and 6N2P Russian tube).
The screen/pin 9 is grounded, but after a while the noise increases a lot.
I had no idea why, so i tried several tubes of that type - no success.
Yesterday i changed the plate current to 0.7 and 1.0mA. The noise decreased a lot.
Now my question: Has anybody else seen this problem?

regards

Frank
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Old 27th January 2013, 07:58 PM   #2
Ketje is online now Ketje  Belgium
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Probably you changed the current by making the cathode resistance smaller.
If there is noise comming from the heater it is now more shortcicuited to gnd (or supp) and has less influence.You could test this by putting a capacitor between cathode and ground.If the noise disappear it came from the heatercicuit.
Mona
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Old 28th January 2013, 04:57 AM   #3
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Thanks for your answer.
I'm not shure, the noise is hiss(like pink noise), not hum.

regards,

Frank
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Old 28th January 2013, 10:56 AM   #4
roline is offline roline  United States
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I prefer 12BH7, 7062, JAN6414, 12AU7, 6N6Pi, for phase splitters running at higher bias, ~5ma. 6N6Pi is a favorite in this application, but a power monger....
I also prefer to run 12AX7, 12BZ7 and 7025 tubes around ~2mA. I've found Ei ECC83 long smooth plates to be good for low noise (both hum, hiss) in a RIAA phono amp front end.
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Old 28th January 2013, 03:13 PM   #5
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I have used 6N2P-EV with 0.3 mA in RIAA front end and with no hiss problem.
Actually the hiss level was higher with higher anode current.

At what signal level your stage works ?
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Old 29th January 2013, 07:31 AM   #6
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Quote:
Originally Posted by artosalo View Post

At what signal level your stage works ?
Input was 0.087Vrms, Output 1.64/1.63Vrms(at 1kHz) for testing.
More Output makes the driver clip.

regards
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Old 29th January 2013, 01:11 PM   #7
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Basically I wanted to know do you plan to use this 6N2P at the line levels or at RIAA levels.
At line levels the noise is never a problem. Usually S/N is some 100 dB at well built line stage.
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Old 30th January 2013, 07:09 AM   #8
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Quote:
Originally Posted by artosalo View Post
Basically I wanted to know do you plan to use this 6N2P at the line levels or at RIAA levels.
At line levels the noise is never a problem. Usually S/N is some 100 dB at well built line stage.
Line level.(Input stage of power amp)
I grounded the input and listened to the speaker.
There was certain amount of noise, decreasing with more plate current.
Disconnecting the input/LTP stage from power stopped the noise, so it
is the LTP - not the driver stage that makes the noise.

regards
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Old 30th January 2013, 01:57 PM   #9
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Are you using a grid stopper?

It could be oscillating.
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Old 31st January 2013, 08:51 AM   #10
FLT is offline FLT
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Quote:
Originally Posted by scott17 View Post
Are you using a grid stopper?

It could be oscillating.
Yes, i have gridstoppers.
Oscillation was my first thought, but the noise disappeared with higher plate current.

regards

Frank
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