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The best tube pre from Vietnam - 818 Pre

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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!


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Joined 2004
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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.)

Were it me I would put a large capacitor across the CCS, were it really me I would use fixed bias (batteries?).. :D 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.)
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!


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