Bias JJ 6V6?

polifemo

I´ve read that JJ 6V6´s need to be biased differently than other brands of 6V6´s.

In the building instructions for the A15Mk2 the recommendation is 35mV.
Does this apply to the JJ´s as well?

Could anyone please explain how different bias settings will affect the sound!?

(My B+ is 310V and I´ve biased the tubes at 32mV)

Thanks

MAD

Hi polifemo,
what do you mean with "they need to be biased differently"? I've made no change, when I switched from JJ to TAD tubes, the 35mA is ok for both 6V6 types. When you bias the 6V6 "hot" (higher cathode current), they sound different as when biased "colder". It's common sense, that more cathode current results in "warmer" sound, but IMHO you need to listen carefully to hear that...
Regards,
Martin

polifemo

Zitat von MAD;243333

Hi polifemo,
what do you mean with "they need to be biased differently"?
Regards,
Martin

I´ve seen a diagram somewhere (Tubetown?) stating that JJ 6V6´s should be biased really "low". (Around 20mV if I remember correctly... can´t find the diagram)
On Eurotubes I´ve read the opposite:

A note to JJ 6V6 users; The JJ 6V6's can be biased as high as 45mv at the test points in Hotrod Deluxe's but most of these amps will only hit about 30mv but even at this setting they sound great. If you want to really push them then you need to drop the value of the final bias resister down by about 20%. A bias setting between 30 to 45 is best for the JJ 6V6's.

MAD

Hi polifemo,
given the same voltages and circuit values a JJ 6V6 only can be biased differently from other 6V6, if the limiting values (power dissipation) are different. So when the Hotrod Deluxe is "opimized" for a 6V6 with lower limiting values, it's possible, that you can change the bias to let the JJ 6V6 have more free running cathode current. But this is just in this case and not generally!
Regards, Martin

polifemo

Thanks Martin!

Ps Did you see my amp?
It´s a real beauty

[Blockierte Grafik: http://i26.photobucket.com/albums/c109/prof2915/IMG_1874.jpg]

[Blockierte Grafik: http://i26.photobucket.com/albums/c109/prof2915/IMG_1875.jpg]

and great sounding as well ds

MAD

Looks Great!
Regards, Martin

JHS

Laut JJ-Datenblatt benötigen die 6V6 etwa 30% weniger Strom (ca. 22-25mA im Class-AB-Mode). MmN ist das aber nur ein Tippfehler. Diese Röhren müssten dann bei 35mA bereits abrauchen, bzw. würden die Gitter glühen und eine korrekte BIAS-Einstellung wäre dann bei vielen Amps gar nicht mehr möglich (zumindest ohne Modifikation).

Gruß, Jürgen

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