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Old 21st June 2009, 04:50 PM   #1
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Default 6N6P - recommended operating point

Yesterday I bought some 6N6P double triodes on Ebay. I have never used this tube before and want to use them in a line stage.

In the past I have used the Sovtek 6N30 a lot and really like this tube. But its characteristics are not the same as 6N6P. So I donít expect the 6N6P to be a drop in replacement for the 6N30.

I did a lot of experimentation with the 6N30, and know how important a good chosen operating point is, to bring a triode to its full sonic potential.

Can anyone give a recommendation for the 6N6P. What is a good operating point to start with? The anode load will be a Constant Current Source, and the cathode will be self biasing or constant voltage.

Peter
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Old 21st June 2009, 06:29 PM   #2
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hey-Hey!!!,
I've gotten good results from anode current between 10 and 15 mA using a CCS load. LED's in the cathode for bias, and liked it with two or three of them in series. That puts anode voltage in the neighborhood of 150V, give or take a bit.
cheers,
Douglas
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Old 21st June 2009, 09:24 PM   #3
Gordy is offline Gordy  United Kingdom
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And now the votes from the East Anglian jury...

16mA CCS
-3 V via bypassed cathode resistor
110 V anode

Rp worked out to about 1.8 k Ohms

Loaded with 4.3 k Ohms (30 Ohm headphone through 12:1 transformer)

Worked fine !

This may be useful to you ( and a thousand lurkers! )...
http://klausmobile.narod.ru/testerfiles/6n6p.htm
http://www.klausmobile.narod.ru/testerfiles/index.htm
http://www.klausmobile.narod.ru/indexe.htm
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Old 21st June 2009, 10:48 PM   #4
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I use them in differential pairs, and have found the higher the current, the better (Rp is lower). 20mA is great, 22mA is better. Based on reasonable dissipation, this limits your plate voltage to less than 150V, I typically run with 0C3 or 0D3 regulation.

As a result of this O/P, the input signal is somewhat limited, as grid voltage is between 3 and 4 volts. So I end up using in my D/A and/or first stage of power amp.

Good luck. This tube is definitely in the "biggest bang for the buck" group.
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Old 22nd June 2009, 12:54 AM   #5
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Ha ha ha, everything between 10mA and 22mA suggested.

And they are all correct.

I have experimented quite a bit with the 6N6P and found that there are sweet spots scattered all along the current line. My favorite are 14.5mA, 16mA and 24mA. The characteristic of the sound is different for each sweet spot so your sweet spot will depend on what you like. Generally, in my circuits, the lower current will give a more delicate, clear presentation while the higher current will give a fuller, more robust presentation.

The plate-to-cathode voltage and bias also make a difference. However, I have found, in my circuits, that the plate current makes much more of a difference than either the plate-to-cathode voltage or the bias. I have had good luck by first finding the current that I like and then experimenting with the plate voltage and bias to fine-tune the sonic presentation.

Dave
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Old 22nd June 2009, 06:55 AM   #6
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Thank you all for the very useful replies!! I will investigate these settings when my 6N6P have arrived. I have a test board with adjustable CCS and adjustable bias, so itís easy to try all sorts of different settings.

For those who use bypassed cathode resistors or LED bias, try to bypass them with tantalum capacitors. I know these capacitors are detested by the audio community, but when I tried them (always curious as I am, and have hundreds of them lying around) as a cathode bypass and compared them to Elna Silmic, I was shocked by the sonic difference! With the tantalums the sound became very refined and dynamic at the same time.

Dave, what you describe about different anode currents is exactly what I experienced with the 6N30. Indeed it sounded more delicate with lower currents and more robust with higher currents.

But adjusting the bias voltage to an optimal point is also very important. What I found is that by raising the bias voltage the soundstage can be opened up by quite a margin! The limit is anode voltage and dissipation you find acceptable.

What anode dissipation do you guys accept as a maximum? My limit is always around 60% of the specified maximum anode dissipation to extend service life.

Peter
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Old 22nd June 2009, 11:21 AM   #7
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On a $2 tube, I run them at 80% without worry.
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Old 22nd June 2009, 01:49 PM   #8
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I don't worry about dissipation either - I just keep them under the limit.

One other thing - I have found that the sample-to-sample variation of the tube parameters varies quite a bit more with the 6N6P than with some of the other Russian tubes, like the 6N1P, 6N23P and 6H30. The good news is that the performance seems to be consistent with a given current. So I find the current and bias that I like and let the plate-to-cathode voltage be whatever it is. Of course, this is with the circuit I use - a differential pair with CCSs in the plates. YMMV with other circuits.

Dave
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Old 22nd June 2009, 02:25 PM   #9
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Good to have you here, Dave. You've been immensely helpful on the K&K forum; hope you continue to contribute.
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Old 22nd June 2009, 02:37 PM   #10
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Hi Dave


Sorry for the offtopic question but you mentioned sample to sample variations between tubes. I just got a bunch of 6H30s from a reputable distributor and it's quite the horror story. Forget comparing different samples; even the two triode sections vary in emission between 20% and 60%. Does this sound normal or have i got some of ARC, Lamm and BAT's rejects? I am using them in a differential with a ccs in the tail so it's not a real disaster but as common cathodes this sections are simply unusable.
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