6N1P

[llan]

I want to use a 6N1P valve as a line input and a concertina phase splitter, having
280 volts on the B side of the HT could any one suggest the resistors for the plate and cathode voltages so as to obtain the least distortion.

llan

 

[LinuksGuru]

Take a look at improved Williamson Amplifier, it uses DC coupled 6SN7 input and concertina. You can replace 6SN7 with 6N1P.

 

[artosalo]

How much drive voltage you need from 6N1P concertina ?
Which output tubes ? 280 V as +Ub is quite low.

 

[tinitus]

280 V as +Ub is quite low.

and I thought 6N1P would want it even lower ?

 

[artosalo]

With higher +Ub the output can be higher as well. Isn't this obvious ?

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

EDIT: When R2 = 1k8, max. output is some 28 V.

 

[llan]

Thanks for your input, my line input stage as a 47K on the plate and a 1K on the cathode the other half used as a phase splitter as two 33K resistors one for the
plate and one for the cathode to drive a couple of 6L6 valves, is there any way to improve this concertina phase splitter or do you have to use a better type phase splitter for lower distortion and a better top response, the Radford 25 watt amp used a ECF82 as a phase splitter I believe this was done to improve the high frequency response.

Llan

 

[tinitus]

how about using 6n6p/ecc99 instead ?

....is there any way to improve this concertina phase splitter....
Llan

 

[artosalo]

...my line input stage as a 47K on the plate and a 1K on the cathode the other half used as a phase splitter as two 33K resistors one for the plate and one for the cathode to drive a couple of 6L6 valves, is there any way to improve this concertina phase splitter or do you have to use a better type phase splitter for lower distortion and a better top response...
Llan

I understand that your 6N1P amplifier stage is direct connected to cathodyne.
If this is correct, this is the reason for high distortion.
To make well designed and well performing amplifier/phase splitter you should use a capacitor between the stages and bias both to optimum.
I already gave you a schematic of such cathodyne.
The frequency response of cathodyne stage is beyond 100 kHz, so should not be a problem.

You told in the first post that the supply voltage is 280 V. What is the supply voltage for the 6L6 output tubes ?

 

[llan]

Sorry, I made a mistake, I have two amps one both using the concertina phase splitters, the one with the 280 B plus volts uses EL84s as push pull output the other uses two 6L6s in the out put this amp as 365 volts on the plates of the 6L6s and the B plus is 350.

Yes there are both DC coupled, I have seen this being used in other valve amps why is it important to use a coupling cap instead of it being dc coupled how does this lower the distortion.

I take your point about the 6N6P/ECC99 would this be a better valve for this position.

Llan

 

[artosalo]

...Yes there are both DC coupled, I have seen this being used in other valve amps why is it important to use a coupling cap instead of it being dc coupled how does this lower the distortion....
I take your point about the 6N6P/ECC99 would this be a better valve for this position.

Llan

When the voltage amplifier stage is operating at minimum distortion point, its anode voltage is, say 150 V for example.
The optimum bias voltage of a concertina at 280 V +Ub is much smaller, say 80...90 V.
If you direct connect this 150 V to concertina, its output voltage is highly limited. On the other hand, if you bias the voltage amplifier so that its anode voltage is 90 V, the result is distorted output signal at the voltage amplifier.
Therefore individual biasing is necessary in most cases.
Direct connection works well with some pentodes as voltage amplifiers because these operate at low anode voltage.
Also 12AX7 is good with direct connection if small driving voltage is required.

There is basically no difference if 6N1P or 6N6P is used as a concertina, because it has full negative feedback that minimizes the differences between used tubes/types.

 

[Tyimo]

Hi Artosalo!

Therefore individual biasing is necessary in most cases.

Could you show me such a circuit (capacitor coupled) with B+ 260Vdc?

greets:
Tyimo

 

[artosalo]

Here you go.
If the cathode voltage of the phase splitter is above, say 75 V, you can decrease it by increasing the value of R2. Optimum is some 60...70 V.

 

[Tyimo]

Thanks!
Is this biased to 3mA? Isn't it not too low?

 

[artosalo]

Notice that I modified the circuit one minute ago.

What output tubes you plan to use ? Fixed or cathode bias ?

EDIT: I was a bit hasty with the simulation. The actual max. output is 30 Vrms with 0.62% THD.

 

[Tyimo]

Thanks!

I was interested it only in theory.
If I would use it then it would be the attached schematic.

 

[sser2]

"Replacing any coupling capacitors with a well designed and correctly matched driver or interstage transformer yields an almost shocking improvement in sound..." Peter Qvortrup

This quote is highly relevant to a phase inverting stage.

 

[Fenris]

Tyimo is right on. That schematic is from Broskie and I've used a modified version of it before with great success: Just what the world needs - another EL84 amp

You could also try replacing the anode resistor with a CCS and/or the cathode resistor with a red or yellow LED.

The amp I'm working on does something similar. It's a PP EL-84 and uses a 6N1P as the driver and phase splitter, but with an order of magnitude lower distortion.

 

[Tyimo]

Hi!

I just wanted to know what would be the ideal bias for the 6N1P in this Tubcad circiut with a lower voltage. say ca. 250-260 B+.

 

[Fenris]

Aim for half of B+. 25-26K for the anode load and the same 340 ohms on the cathode. Or better yet a red LED on the cathode.

 

[Tyimo]

Thanks!
What about the concertina stage?