Hi, I have a three stage phono preamp, v1 and v2 are ecc83 and in v3 I am implementing a Russian 6n6p.
The scheme is a classic ear834 type, or the old CJ and AR type preamps.
V3 is configured as follower cathode, DC coupled to v2.
I have a stabilizer circuit which provides two different b+.
One of 310v for v1 and v2 and another of 300v for v3 (6n6p).
Theoretically I can vary these voltages a little by acting on zener and / or resistors.
I would need some advice and hints for polarizing the 6n6p please. Here on various 3ds I have seen anodic voltages (6n6p) from 180v to 300v.
I also know with certainty that the 6n6p works well with currents of around 15mA.
On the v2 anode I have about 115 / 120v (Ra = 330K) which are reflected in the input of the 6n6p grid. I was wondering if you have polarizations to recommend ...
Are there too many 300v on the anode?
115 / 120v on the grid are too many?
Well if you give me a little help ...
😀 Thanks
The scheme is a classic ear834 type, or the old CJ and AR type preamps.
V3 is configured as follower cathode, DC coupled to v2.
I have a stabilizer circuit which provides two different b+.
One of 310v for v1 and v2 and another of 300v for v3 (6n6p).
Theoretically I can vary these voltages a little by acting on zener and / or resistors.
I would need some advice and hints for polarizing the 6n6p please. Here on various 3ds I have seen anodic voltages (6n6p) from 180v to 300v.
I also know with certainty that the 6n6p works well with currents of around 15mA.
On the v2 anode I have about 115 / 120v (Ra = 330K) which are reflected in the input of the 6n6p grid. I was wondering if you have polarizations to recommend ...
Are there too many 300v on the anode?
115 / 120v on the grid are too many?
Well if you give me a little help ...
😀 Thanks
120V on the grid is not too much, neither is the 300V on the anode, but you could drop it a bit like 260...270V. What is more interesting is the cathode resistor (or constant current source, CCS), it will dissipate 1.8W. You need to use a 8.2k resistor at least 5W. The tube (one half) will dissipate some 2.5W.
In some DC coupled designs I have seen a reverse polarized diode between the grid and cathode, to prevent positive grid voltage and arcing at power-on.
In some DC coupled designs I have seen a reverse polarized diode between the grid and cathode, to prevent positive grid voltage and arcing at power-on.
Hi! Yesterday I wrote the post..then after a few changes of zener (for B+1 and B+2) and resistors are, currently, at this point:
.
Before 6n6p there was a 12ax7 (original project) .. changed to 12at7 .. changed to 12au7 .. changed to ecc88 ... changed to 6n1p ... now 6n6p and this tube I want (I would) keep.
The load I drive with the preamp is 8Kohm with 2,5mt of cable (good quality).
I don't know which way to go ... with polarization 😕
I made some calculations to be able to have the negative grid since the b+1 of the follower cathode is lower than the other, and, normally, I always see the opposite in the diagrams ... that is, the follower cathode is the one with the higher voltage ..
According to my accounts it should be biased with 14mA, I believe (129.9v: 9270ohm = 14ma).
I think (I suppose) we can raise it a little bit more, I would like at least a good 15mA.
Another solution was to lower the voltage on the anode of v2 but then so I think that the performance (working point) worsens, so I preferred not to touch the v2 stage.
Obviously the resistances are temporary, defined the values, I decide the type and power. Also the output caps, currently a parallel of 4.7uF total, will be replaced with Russian 10uF PIOs traveling towards me.
Even the "PCB stabilizer", the one with the zener, will be replaced with a printed PCB (already ready).
Ahhh I forgot, for the voltage between the cathode and the filament (Vkf), which should be maximum 100v, there is no problem because I am using a divider to lift it .. at 60v from the ground.
Forgive me if I say nonsense, I'm a beginner!
@ Icsaszar: Yes, I have often seen that diode you say .. in different schemes .. even of AR and CJ .... If it is useful, in the end, I will implement it.
Sincere thanks guys and happy holidays! 😎
PS: A couple of photos of my nuclear power plant😱😀:
.
.
.
Before 6n6p there was a 12ax7 (original project) .. changed to 12at7 .. changed to 12au7 .. changed to ecc88 ... changed to 6n1p ... now 6n6p and this tube I want (I would) keep.
The load I drive with the preamp is 8Kohm with 2,5mt of cable (good quality).
I don't know which way to go ... with polarization 😕
I made some calculations to be able to have the negative grid since the b+1 of the follower cathode is lower than the other, and, normally, I always see the opposite in the diagrams ... that is, the follower cathode is the one with the higher voltage ..
According to my accounts it should be biased with 14mA, I believe (129.9v: 9270ohm = 14ma).
I think (I suppose) we can raise it a little bit more, I would like at least a good 15mA.
Another solution was to lower the voltage on the anode of v2 but then so I think that the performance (working point) worsens, so I preferred not to touch the v2 stage.
Obviously the resistances are temporary, defined the values, I decide the type and power. Also the output caps, currently a parallel of 4.7uF total, will be replaced with Russian 10uF PIOs traveling towards me.
Even the "PCB stabilizer", the one with the zener, will be replaced with a printed PCB (already ready).
Ahhh I forgot, for the voltage between the cathode and the filament (Vkf), which should be maximum 100v, there is no problem because I am using a divider to lift it .. at 60v from the ground.
Forgive me if I say nonsense, I'm a beginner!
@ Icsaszar: Yes, I have often seen that diode you say .. in different schemes .. even of AR and CJ .... If it is useful, in the end, I will implement it.
Sincere thanks guys and happy holidays! 😎
PS: A couple of photos of my nuclear power plant😱😀:
.
.
Last edited:
Looks fine as it is, but you can lower the cathode resistor a bit to get 15mA if desired.
The plate dissipation now is 1.75W.
The plate dissipation now is 1.75W.
Last edited:
Thanks for reply..
The only thing I know that should be fine is the current, 15mA.
The voltage b + is without any particular calculation, current 185v.
The voltage that I find on the cathode I made sure that it is 2v or a little higher than that of the grid .. but this too is random.
The -2v are "random". There is no b + voltage and no better grid negative voltage point, ie for better yield, linearity .. distortion .. etc ..?
Doing the math I see that on the anode there are practically (about 185v - 130v) about 55v. Are they the ideals?
You advised me Rk from 8.2k = 15.85mA, but if I lower Rk I think then the -2v on the grid changes, am I wrong?
Thanks again. 🙂 ..and sorry for my bad english
The only thing I know that should be fine is the current, 15mA.
The voltage b + is without any particular calculation, current 185v.
The voltage that I find on the cathode I made sure that it is 2v or a little higher than that of the grid .. but this too is random.
The -2v are "random". There is no b + voltage and no better grid negative voltage point, ie for better yield, linearity .. distortion .. etc ..?
Doing the math I see that on the anode there are practically (about 185v - 130v) about 55v. Are they the ideals?
You advised me Rk from 8.2k = 15.85mA, but if I lower Rk I think then the -2v on the grid changes, am I wrong?
Thanks again. 🙂 ..and sorry for my bad english
Yes, the Vgk varies with the operating point. Test to see how much output voltage is available
from the cathode follower now. You probably will want a Vgk that is more negative than -2VDC.
See the tube curves here:
https://frank.pocnet.net/sheets/113/6/6N6P.pdf
from the cathode follower now. You probably will want a Vgk that is more negative than -2VDC.
See the tube curves here:
https://frank.pocnet.net/sheets/113/6/6N6P.pdf
Last edited:
Hi, I assume -4v/-4.5v is ok.
I brought the b+ for the 6n6p to 270v. Here I would like to keep it, approx.
With this voltage and setting (through Rk) a current of 12mA/14mA I can no longer get a negative grid voltage lower than -5.5v/-6.3v.
I assume because of the curves of this graph, am I wrong?
It seems that if I want a grid of -4 with 12-14ma I can't have a b+ that high.
To get a -4v with 12-14mA... it looks like I have to have a lower b+ voltage.
I know that if I lower the Ra value of the previous stage or the b + that feeds the previous stage a little, I can get a -4, right? It's the only way, right?
A question:
but does the voltage value in the two graphs mean the one between b+ and gnd or the one on the valve pins, between anode and katode....after Rk (in case of cathodo follower)?
Many Thanks
I brought the b+ for the 6n6p to 270v. Here I would like to keep it, approx.
With this voltage and setting (through Rk) a current of 12mA/14mA I can no longer get a negative grid voltage lower than -5.5v/-6.3v.
I assume because of the curves of this graph, am I wrong?
It seems that if I want a grid of -4 with 12-14ma I can't have a b+ that high.
To get a -4v with 12-14mA... it looks like I have to have a lower b+ voltage.
I know that if I lower the Ra value of the previous stage or the b + that feeds the previous stage a little, I can get a -4, right? It's the only way, right?
A question:
but does the voltage value in the two graphs mean the one between b+ and gnd or the one on the valve pins, between anode and katode....after Rk (in case of cathodo follower)?
Many Thanks
Last edited:
Tube data is given as the voltage of one pin relative to another, with the cathode grounded (0V).
The grid voltage is also relative to cathode (ground). All these interact, and the supply voltage and the
plate resistor (and the direct coupling) impose constraints on what can be done. Many circuits do not
ground the cathode, and so need a change in perspective.
http://www.tubebooks.org/Books/Preisman_graph.pdf
The grid voltage is also relative to cathode (ground). All these interact, and the supply voltage and the
plate resistor (and the direct coupling) impose constraints on what can be done. Many circuits do not
ground the cathode, and so need a change in perspective.
http://www.tubebooks.org/Books/Preisman_graph.pdf
Last edited:
Don't worry about the cathode voltage. It will follow the grid AC voltage, and the grid-to-cathode DC voltage will be constant.
Thanks...
Ahh ok.
So the voltage on the grid will automatically position itself according to the curves of the datasheet, regardless of the Rk value and regardless of the voltage coming from the anode of the previous stage (DC coupled)?
The only way to vary the negative of the grid is by acting on the supply voltage b +, that is the one I have between b + and GND?
The higher the voltage, the more the grid negative rises (with the same current) ..- 4 ...- 5 ...- 6 ...- 7 ... etc.
If, on the other hand, at a given "high" voltage ... I increase the current, will the grid negative go back down, as per the "right" graph?
Do I choose the value of Rk solely to decide how much current I decide for the polarization?
The answers will probably always be "yes". I hope!
It means I understand.
Thanks!
Ahh ok.
So the voltage on the grid will automatically position itself according to the curves of the datasheet, regardless of the Rk value and regardless of the voltage coming from the anode of the previous stage (DC coupled)?
The only way to vary the negative of the grid is by acting on the supply voltage b +, that is the one I have between b + and GND?
The higher the voltage, the more the grid negative rises (with the same current) ..- 4 ...- 5 ...- 6 ...- 7 ... etc.
If, on the other hand, at a given "high" voltage ... I increase the current, will the grid negative go back down, as per the "right" graph?
Do I choose the value of Rk solely to decide how much current I decide for the polarization?
The answers will probably always be "yes". I hope!
It means I understand.
Thanks!
The book that I posted for you will be most helpful. All of the parameters of the circuit
will interact in setting the DC operating point.
will interact in setting the DC operating point.
Thanks, yes .. I started reading it yesterday.
I must say, however, that it is very complex and, being in English, it gets complicated!
Calmly I will continue to read it. 🙂
I must say, however, that it is very complex and, being in English, it gets complicated!
Calmly I will continue to read it. 🙂
No, yes, yes, yes.
Rk sets the current flowing through the tube. Ua sets the operating point, determining Ugk and dissipation (and linearity in some extent).