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6N3 Preamp Question

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I found this schematic for a preamp that I want to use to drive 2 Mark IV mono amps,using an iPod for a source,so I don't need any gain but would like to have someting for both impedance matching,and switching for other sources. The schematic looks like a typical cathode follower,but I have a question,the second triode is directly coupled to the other triode,I'm not sure what I'm missing here,and would like suggestions on other mods if there needs to be,Thanks a million!!
 

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I found this schematic for a preamp that I want to use to drive 2 Mark IV mono amps,using an iPod for a source,so I don't need any gain but would like to have someting for both impedance matching,and switching for other sources. The schematic looks like a typical cathode follower,but I have a question,the second triode is directly coupled to the other triode,I'm not sure what I'm missing here,and would like suggestions on other mods if there needs to be,Thanks a million!!
This is a "direct coupling", there is no need for a coupling capacitor and grid leak resistor ... There is 95V at the plate of the first tube and the grid of the second one, 99V at the cathode of the second tube, then the "bias" is -4V ...

The double triode is a chinese 6N3 or 6N3P or russian 6H3Π but a preamp like that can be made with any good double triode if you adjust the resistor to get the good bias and currents for the best operating points. R13 is a negative feedback resistor to reduce distortion.

The rectifier suppose to be a 6Z4 Shuguang but I think the pinout is wrong ... Anyway, you can use just about any full wave tube rectifier for this preamp, for example a 6CA4. You will just have to adjust the voltage dropping resistor "RO" 3K to get the 241V supply, for two channel of course because this schematic is for a monophonic preamplifier !

Alain. :)
 
Also, people here say 6N3P is terrible for audio
This is not the case. 6N3P (ев) (made in Russia) good sounding tube. I successfully used it as a driver in a PP EL84 amplifier.

In the power supply, I would have applied the choke and parallel with the electrolytic capacitors, I would be hooked up film capacitors 2-4 uF / 400V.
PS
You do not like cats?

You just do not know how to cook them!
:D
 
Last edited:
This is not the case. 6N3P (ев) (made in Russia) good sounding tube. I successfully used it as a driver in a PP EL84 amplifier.

In the power supply, I would have applied the choke.

PS
You do not like cats?

You just do not know how to cook them!
:D

I remember Wavebourne saying so, I just have them in a cheap Yarland I bought. So he said there are huge stocks and people in ex-CCCP want to get rid of them. It is not a coincidence you only find them in the cheapest amplifiers

PS your comment ruined my day, not that I like cats.
 
This is not the case. 6N3P (ев) (made in Russia) good sounding tube. I successfully used it as a driver in a PP EL84 amplifier.

In the power supply, I would have applied the choke and parallel with the electrolytic capacitors, I would be hooked up film capacitors 2-4 uF / 400V.
PS
You do not like cats?

You just do not know how to cook them!
:D
I am very interested using russian tubes in my audio projects exactly because there some very good ones, they are not very expensive and I am not rich ... Let the snobs spend their money buying all the 2A3 and 300B ... :D

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:p

Alain. :trapper:

 
I have an Audio Experience preamp which uses 1 x ECC82 and 2 x ECC83s. I didn't like the slightly hard, strident sound of this preamp and I tried quite a few different ECC83s before I gave up and took a gamble and replaced them with Russian 6N3Ps (making the necessary alteration to the heater wiring). In this preamp these 6N3Ps sound great with no hard edge so I'm more than happy.
 
I have an Audio Experience preamp which uses 1 x ECC82 and 2 x ECC83s. I didn't like the slightly hard, strident sound of this preamp and I tried quite a few different ECC83s before I gave up and took a gamble and replaced them with Russian 6N3Ps (making the necessary alteration to the heater wiring). In this preamp these 6N3Ps sound great with no hard edge so I'm more than happy.
The 6N3P linearity at about -2V bias and 4 to 8ma current with up to 1 V peak input signal look very good to me :

An externally hosted image should be here but it was not working when we last tested it.


Alain. :)
 
Hello,
I believe that now is the time to make the transition from tubes to JFETs. Tubes have high distortion, operate at high dangerous voltage and are far too noisy. Peers seek Amperex 6DJ8 / ECC88 tubes because they are rare and expensive not because they make good amplifiers.
By any metric 2SK170’s make better amplifiers.
Or I guess as long as surplus Soviet tubes are cheep let them play.
DT
 
Alan, I found that in actual measurements the LED bias/Anode current source produced less distortion than bypassed cathode bias (6N1P-EV and 6N3P). I agree that unbypassed cathode bias would most likely produce less distortion than either. However, you are trading off gain for distortion.

I also have no doubt that it varies depending on tube type.

It is possible that a single stage with LED bias and Anode current source load may produce less distortion with sufficient gain where otherwise two stages with cathode bias unbypassed would be needed.

When the only tool you have is a hammer, everyting begins to look like a nail.

Spice simulators are nice to get in the ballpark. Measurements are better, and listening is best.
 
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Hello,
I believe that now is the time to make the transition from tubes to JFETs. Tubes have high distortion, operate at high dangerous voltage and are far too noisy. Peers seek Amperex 6DJ8 / ECC88 tubes because they are rare and expensive not because they make good amplifiers.
By any metric 2SK170’s make better amplifiers.
Or I guess as long as surplus Soviet tubes are cheep let them play.
DT

Try to swing a couple of hundred volts peak to peak with one of your JFETs.. :D

Actually there are plenty of tubes offering very high levels of performance without the hint of solid state that some of us here would find objectionable. I'm talking about tubes like the 5842, and triode connected 7721/D3A, 7788/E810F, and C3G. Yes less practical and more expensive than a 2SK170 but a bit more fun? Transfer function of JFETs is fundamentally pentode like which results in a different distortion spectra. (SITs are an exception, but expensive and hard to get.)

In any event this is the tube/valve forum where us tube diehards hang out.. :D
 
Try to swing a couple of hundred volts peak to peak with one of your JFETs.. :D

Actually there are plenty of tubes offering very high levels of performance without the hint of solid state that some of us here would find objectionable. I'm talking about tubes like the 5842, and triode connected 7721/D3A, 7788/E810F, and C3G. Yes less practical and more expensive than a 2SK170 but a bit more fun? Transfer function of JFETs is fundamentally pentode like which results in a different distortion spectra. (SITs are an exception, but expensive and hard to get.)

In any event this is the tube/valve forum where us tube diehards hang out.. :D

Take the output transformers out of it, where do you need to swing a couple hundred of volts? For a line stage like we are speaking of here more than a couple of volts may be too much.
The distortion spectra of triodes or JFETS depend on the bias point selected. JEFET’s need not be biased to the flat end of their performance curves where they look like pentodes. The left hand end of the JFET curve family slope and look more like triodes and produce even, mostly 2nd, harmonics. It is all fun!

The point is that JFET’s need friends too. That will leave more tubes to us diehards. I like 6BQ7’s and black plate 5670’s. The 5670 will roll right in the circuit in post number 1.

DT
 
Alan, I found that in actual measurements the LED bias/Anode current source produced less distortion than bypassed cathode bias (6N1P-EV and 6N3P). I agree that unbypassed cathode bias would most likely produce less distortion than either. However, you are trading off gain for distortion.

I also have no doubt that it varies depending on tube type.

It is possible that a single stage with LED bias and Anode current source load may produce less distortion with sufficient gain where otherwise two stages with cathode bias unbypassed would be needed.

When the only tool you have is a hammer, everyting begins to look like a nail.

Spice simulators are nice to get in the ballpark. Measurements are better, and listening is best.
I am not crazy about LED bias but I'm a anode current source load fan ( like a DN2540 ). Since the only AC load is the grid leak resistor of the next stage, the gain is much higher and since the load line is more "horizontal", there is less distortion, specially for pentodes and JFET.

Sometime, preamp lower distortion is more important than high gain, all depend on the power amplifier and sources need. Many circuits need many tubes stages anyway, for example, if there is tones controls.

Not everybody own a good distortions analyser, there is some software ones working with the sound card but that's not very precise under 1% because average sound cards make more distortions than that ... I got some scopes home but it is difficult to visually evaluate small distortions with them.

Simulators can be very precise but most Spice models found on the net are not. I always generate the tubes and semiconductors curves with mine and compare them point to point with their datasheets curves, of courses, those curves are average for the parts types and sometime very differents from real parts but it is better than nothing ... Simulators are the best tools ever made for any kinds of electronic designs, I wish I have one when I build my firsts tubes amplifiers 40 years ago but the first DOS ones only appear in the '80's ...

Alain. :)
 
Try to swing a couple of hundred volts peak to peak with one of your JFETs.. :D

Actually there are plenty of tubes offering very high levels of performance without the hint of solid state that some of us here would find objectionable. I'm talking about tubes like the 5842, and triode connected 7721/D3A, 7788/E810F, and C3G. Yes less practical and more expensive than a 2SK170 but a bit more fun? Transfer function of JFETs is fundamentally pentode like which results in a different distortion spectra. (SITs are an exception, but expensive and hard to get.)

In any event this is the tube/valve forum where us tube diehards hang out.. :D
Personnally, I will never use a field effect transistor directly in the "sound path" of a good quality tubes amplifiers, just as constant current source. Like you said JFET are not good for big voltage swing, so a power tubes driver have to be a tube too ... A power tube driver can be a high voltage MOSFET but it will usually be a poor quality hybrid circuit ...

JFET and MOSFET curves are similar to pentodes curves but that don't mean they produce the same sound, transistors commutation and thermionic effect in tubes are two very different principles.

Alain. :)

P.S. I wonder why so many peoples talk about the 2SK170 like if it was a "magic" JFET ... It is just a popular myth, they are not very linear and not fantastic in a common source amplifier stage ... And there are so many others much cheaper to discover ... :D
 
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