Bias adjustment for Jadis DA5

Thank you, Jacques.

Yes, for the sake of the output transformers, which are a bit of an achilles heel of the JOR, you should always connect a transformer coupled tube amplifier to a load. Loudspeakers will work fine. You don't need to have any input connections coming into the amplifier, however.

If you feel comfortable with the procedure, you might want to bias to the specified value, let the tubes break-in, and they increase the bias to 150 mV, and see if you notice a nice sonic improvement.

By the way, in my opinion, properly tubed and set-up, the JOR is one of the finest sounding amplifiers one will encounter.

Best of luck!
Joe

So Trelja, I did the job..
You are right, the worst was the opening..(I modified also the bottom, making 8 one inch holes in regard of the resistance and the potentiometers)

Talking about the job...The 5,62 resistances gives 6.2 when measured. The all four..(old age??)

The 2Ko potentiometer were a bit touchy.. Not so easy to make the step 2 of the bias equilibration (OmV between the two pin 3..) Nevertheless I put 145 mV bias (and less the 10mV between the 2 pin 3)

You are right the listening is incredible.. very clear and precise. At least with Jazz (Exemple Midnight Sugar, or Yim Hok-man drums incredible record). Then I went back to Piano and discovered that the "Lang Lang Chopin" (a Sony recording) is somewhat dumped..(etouffé, struggled... I don't know the english name)., It was better with other piano recordings. But neverthess, not so clear as usual..May be.. I have to let time to it...

Can this 145mV bias stay so or is it safer to go back to the traditional 110 mV bias to preserve tube longvity (KT90)

Thank you any way for your help
Jacques

Congratulations, Jacques! Sounds like you've done a fantastic job. From now on, biasing your JOR will be a walk in the park.

Glad to hear you like the sound of the amp. You can keep it biased at 145 - 150 mV. It's still running exceptionally conservative at these settings.

If you want to improve the sonics, when the time comes that the KT90 need to be replaced, I would look into a quad of JJ E34L. The midrange you'll get from this amplifier will be about as good as you will encounter. And, one upgrade you can do right now is to try a pair of Shuguang 12AX7B, which might really open the sound up for you. And, these Shuguangs are incredibly low cost at that.

Merry Christmas!