First, I'd like to say that I cannot recommend my good friend Pierre Gabriel highly enough. We are most fortunate to have him as the North American distributor of Jadis. He is a fantastic person.
Pierre, PLEASE correct me if anything I say here is wrong...
Now, excuse my naivete, but if someone would show my how to post a picture here on Audiogon (do I just include a link to my photobucket.com album?), I can include a photo or two of the resistor that needs to be measured across during the JOR biasing procedure. Robert (mares-mares) lives in Thailand, the document I have is too large to be e - mailed, and I don't want him to have to wait for the mail to reach him there if we can do it simply in this thread.
The picture solves what is the most tricky part when you are inside the amplifier - finding that resistor. The potentiometers are obvious. You simply set the bias to a value between 95 and 120 mV (110 mV being the ideal setting).
I also find there is a lot of confusion as to the requirement of using two multimeters. While I have always used two, doing so with one would be just as efficacious. You are simply trying to make sure that each of the two tubes in the channel stay at 110 mV, as adjusting one could "potentially" throw the value of the other off. I must say that in practice, I have not noticed this being the case (though it was with my Granite 861 amps, but they were super easy to bias as everything was external).
Once you see where the resistor is, the DIFFICULT step of the whole thing becomes actually reassembling the JOR. In fact, my recommendation is to drill additional holes (there's already a lot of them there anyway) in the bottom plate while you have it off that line up with accessing the resistors and pots for each tube. That way, the entire procedure would become a simple no muss, no fuss procedure that would probably be done in about 3 minutes.
As far as time periods go, I think that biasing the amp every year would be good. For someone rolling the 12AX7 tubes, which Roberts wants to do, the difference in gain of the different 12AX7 (and 5751) variants, could potentially alter the bias settings (Pierre could answer this one as I no longer have my JOR to see if it does or does not). But, the type of output tube itself is a big consideration. The Ei KT90 tubes that came with the JOR for a long time are the most rugged, but are not very good sounding. Pierre and I both like JJ E34L and KT88 tubes best in terms of sonics. In my JOR, the E34L produced the BEST midrange I've ever encountered anywhere, though the KT88 will provide more low end and a bit more power. I'll add that I'd been using the new JJ KT77 in my DA60 for its combination of low end and midrange, though since Saturday I've been running the E34L, and am quite happy.
Until I got a tube tester, my JOR sounded fine, other than having to goose up one tube like crazy. It turned out that KT90 tube was shorted (caused no damage to the amp or my speakers), but getting it right sure provided a lot of peace of mind.
Pierre, PLEASE correct me if anything I say here is wrong...
Now, excuse my naivete, but if someone would show my how to post a picture here on Audiogon (do I just include a link to my photobucket.com album?), I can include a photo or two of the resistor that needs to be measured across during the JOR biasing procedure. Robert (mares-mares) lives in Thailand, the document I have is too large to be e - mailed, and I don't want him to have to wait for the mail to reach him there if we can do it simply in this thread.
The picture solves what is the most tricky part when you are inside the amplifier - finding that resistor. The potentiometers are obvious. You simply set the bias to a value between 95 and 120 mV (110 mV being the ideal setting).
I also find there is a lot of confusion as to the requirement of using two multimeters. While I have always used two, doing so with one would be just as efficacious. You are simply trying to make sure that each of the two tubes in the channel stay at 110 mV, as adjusting one could "potentially" throw the value of the other off. I must say that in practice, I have not noticed this being the case (though it was with my Granite 861 amps, but they were super easy to bias as everything was external).
Once you see where the resistor is, the DIFFICULT step of the whole thing becomes actually reassembling the JOR. In fact, my recommendation is to drill additional holes (there's already a lot of them there anyway) in the bottom plate while you have it off that line up with accessing the resistors and pots for each tube. That way, the entire procedure would become a simple no muss, no fuss procedure that would probably be done in about 3 minutes.
As far as time periods go, I think that biasing the amp every year would be good. For someone rolling the 12AX7 tubes, which Roberts wants to do, the difference in gain of the different 12AX7 (and 5751) variants, could potentially alter the bias settings (Pierre could answer this one as I no longer have my JOR to see if it does or does not). But, the type of output tube itself is a big consideration. The Ei KT90 tubes that came with the JOR for a long time are the most rugged, but are not very good sounding. Pierre and I both like JJ E34L and KT88 tubes best in terms of sonics. In my JOR, the E34L produced the BEST midrange I've ever encountered anywhere, though the KT88 will provide more low end and a bit more power. I'll add that I'd been using the new JJ KT77 in my DA60 for its combination of low end and midrange, though since Saturday I've been running the E34L, and am quite happy.
Until I got a tube tester, my JOR sounded fine, other than having to goose up one tube like crazy. It turned out that KT90 tube was shorted (caused no damage to the amp or my speakers), but getting it right sure provided a lot of peace of mind.