6N2P/6Н2П low plate current increases noise?

[FLT]

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

 

[Ketje]

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

 

[FLT]

Thanks for your answer.
I'm not shure, the noise is hiss(like pink noise), not hum.

regards,

Frank

 

[roline]

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.

 

[artosalo]

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 ?

 

[FLT]

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

 

[artosalo]

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.

 

[FLT]

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

 

[scott17]

Are you using a grid stopper?

It could be oscillating.

 

[FLT]

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

 

[pd33]

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 ?

As far as I know the 6N2P differs significantly from the 6N2P-EV. @Threadstarter: Thanks for the links to russian tubes! Great Information! Patrick

 

[catsm58]

Have bought a number of these tubes and built a guitar amplifier to use them, I wired it in such a way that I could switch between 12AX7 and the 6n2p-eb well I got the amp up and running but found the tubes were very noisy, not hum. It seemed to get worse with signal, crackles and fizzes.
They weren't microphonic though I have been thinking I've got duds. I'm pretty sure I bought them along with a bunch of 6V6 equivalents which were pretty much a waste of time. Two out 20 the bases parted company, I went through the rest trying to find a pair that would behave. All in all not a good experience. I have three 6N2P-EB in another amp with a pair of the 6N6C which are noisy as well. Not enough to make it unusable but annoying. There is hiss but the main noise is the crackle fizz which appears under load. I'm thinking that the circuit values around the tube may contribute I'm using the same values I would for the 12AX7 as if I don't like them I can just switch back to the 12AX7. As a guitarist I actually quite like sound of these odd tubes. The one I have just built though I found just too noisy but I am using Dumble ideas for gain. The out puts also are the russian equivalents of the EL36 which I tried because of curiosity. A pair of these produce 60watts. But I did find I had to change the grid stoppers to get rid of blocking. Using sine input was fine until I plugged the guitar in. Maybe the noise is related to using the circuit components we are used to with 12AX7's which means really they are not interchangeable.(other than the heater wiring)