The best tube pre from Vietnam - 818 Pre

[quanghao]

Hello!
Please introduce to you a Pre Amplifier designed by me and has been popular in Vietnam 5 years! And is considered one of the best in pre post in Vietnam. There was a lot of my friends use it, and so far they still love it!
I use a very simple design, using three types of tube are different: 6h30Pi, 6h6pi, 6dj8.
Sounds very realistic detail, balance!

This is a circuit diagram of the 818 pre! Pleas see it!
Thanks

 

[quanghao]

And some all image

 

[mach1]

How many minutes do the tubes last running them at 40mA per section ?

 

[quanghao]

and

 

[quanghao]

How many minutes do the tubes last running them at 40mA per section ?

Tube 6h30 or 6h6 I use 1/2 tube = 20mA!
So one Chanel have 2 tube, per tube 40mA, Total = 80mA!
Thanks

 

[quanghao]

The last time I meet Salas shunt, I use it with all cap MKP!
So I say i love Salas shunt and MKP cap for supply!
I have one image!

 

[quanghao]

One friend live in the California USA, He make 818PRE, and he measure it!

 

[quanghao]

And some image
And Salas shunt measure and my 818Pre

 

[Wavebourn]

Why is such a discrimination: you feed 6N6P with 80V more than 6N30P?

 

[quanghao]

Why is such a discrimination: you feed 6N6P with 80V more than 6N30P?

No!
At anode :
6h30pi = 90V, Ia 1/2 tube 20ma. the sound excellent
6H6pi =170 ,Ia 1/2 tube 15- 20ma, the sound it the best, i see
and 6Dj8 = 90V, Ia =5-7ma, i like

Thanks

 

[Wavebourn]

What about 6N1P?

 

[quanghao]

What about 6N1P?

I not test it, but
6n1p, or 6h1, you can you use for this circuit Anod at 90-100!
Some friend have been use it!

 

[SY]

What's going on in the cathode circuit? Are you switching between bypassed resistor and a non-bypassed CCS?

Have you completed the wiring since those pictures were taken and actually tried the unit out?

 

[quanghao]

What's going on in the cathode circuit? Are you switching between bypassed resistor and a non-bypassed CCS?

Have you completed the wiring since those pictures were taken and actually tried the unit out?

Yes!
That is one option,
If you need Lower Z Out put, Use CCS

 

[SY]

How do you manage lower output Z with a CCS in the cathode?

 

[quanghao]

How do you manage lower output Z with a CCS in the cathode?

Oh! I'm sorry, I'm wrong, CCs as it not down Z out!
Thanks!

 

[quanghao]

This is some PCB, please it! thanks

 

[quanghao]

What about 6N1P?

Hi Wavebourn!
I see you successful about the Pre with tube 6h1, Can you show me please?
I wan test with your advance

Thanks

 

[kevinkr]

What's going on in the cathode circuit? Are you switching between bypassed resistor and a non-bypassed CCS?

Have you completed the wiring since those pictures were taken and actually tried the unit out?

Hi SY,
This is a well known design in Vietnam that apparently a lot of people have built. (I have an audiophile buddy who lives there, so I follow this stuff to some extent.)

Quangho
Were it me I would put a large capacitor across the CCS, were it really me I would use fixed bias (batteries?).. 😀 I would expect the CCS to significantly increase rp (source impedance) and reduce gain, and the LM317 makes a pretty mediocre CCS outside of power output stages, although the fairly high currents probable help here. (Look at some of the very nice CCS designs lurking here.)

 

[quanghao]

Hi kevinkr!

Well thank you!
Well yes, the LM317 can not be the best, I used Jfet replace it! I recently tested the following schematic, and I enjoyed it! 6h30pi particular tube,
Thank you and hope you add comments to this pre!

With tube 6h30 i like:
Anode = 90V, 40mA/ Tube
6h6 I like:
Anode = 170V, 40ma/Tube
This is other circuit, Please see it!
Thanks
Quanghao