Jadis OR bias value for Mullard RL34 and KT88 help


I just swapped my Gold Lion (reissue) KT88 tubes for Mullard EL34's and was vwery surprised that the volume was so much lower. I checked the bias and found it to be less than 10mv while the KT88's had been biased at 110mv.
I rebiased the EL34's up to 90mv and the volume increased to what seemed to be "normal".
I am looking for the correct voltage to bias the new EL34 to in a Jadis Orchestra Reference.
Any help is appreciated.
128x128mattzack2

Showing 21 responses by mattzack2

Trelja.... I'm back again. Heart attack slowed me down a little, but feeling a lot better now.

I ordered the JJ el34 L tubes and should have them in a couple of days.
I was hoping Trelja would have spotted this thread.
I still have the GL kt88, which sound great. I actually am trying el34 based on Trelja's posts.
Thanks Trelja. That's what the manual stated but I just wanted to hear your thoughts since there was such a large difference in readings.
I am trying Mullards (new) because there was no JJ's that I could get my hands on immediately. I have about 12 hours on them so far. The bass is much softer than the kt88. I am not as concerned about that right now, but I am anxious the have the holographic sound stage back. I was wondering if the JJ's took very long to bloom. I also installed a pair of Tungsol 12ax7's at the same time, so I may be overly anxious to hear the same quality that I have been getting.
I am driving a pair of Dali Helicon 800's at 89.5 db effiency which are no problem for the JOR. I even drive them with a 16wpc Carissa 845. I also have some Gemme Tantos that are a little over 90 but I prefer the Dalis
I am hoping to better the sound that I have with the GL kt88's. I love the holographic detail that I get with them. So far the EL34's seem very quiet in the bassiness and I'm thinking that should be improved with different 12ax7 tubes. I'd like to learn how good I can get the JOR to sound.

Which speakers do you have?
I played music all night and when I checked the sound this morning it was starting to fill the room and was emphasing more detail. I am much less skeptical about themnow.
Very interesting .
I will check out those 12ax7's. I just bought these Tungsols but I am going to take your advice on them.
The Mullards have started filling the room and the lesser bass has become a nonissue. I am going to run it mostly Continuos over the rest of the weekend.
They are still breaking in I believe. They did seem to start filling the room nicely a few days ago ( about 100 hrs ago), but they have paused short of the kt88's at this point. I have tried swapping out the TungSol with Mazda 12ax7s's and EH12ax7's and the Mullards seem to still be shy of the holographic richness I am looking for.

I am going to continue burning them in for a while more. But I am considering playing with the bias a little. I have it at 110mv now and was thinking of going to the recommended extremes of 90 and 120mv. What do you think of this plan?
Trelja-

I tweaked the bias up to 120mv and everything opened up immediately. I backed it down to 115mv and it sounds great. Lots more midrange detail and air. Bass seems crisper also but not as strong as kt88's as you mentioned.

Should changing the 12ax7's affect the bias at all?
Thanks....
It it really sounding pretty good right now. It might be interesting to see if it can be safely increased to 140mv or so. I am not concerned with tube life, but I want to avoid burning something else.

I will increase it as soon as I hear from you. It sounds very clear and airy right now.
I plan on doing that this weekend. I will keep you posted. I wish I had a quad of jjel34's to compare.
Hello Doctor. I did order the blue ones.
I also rearranged my listening environment to an area that has no hardwood reflection. The one thing that I feel is lacking is the sensation of being in a totally black void and just having the music suddenly just be there. KT88's did that for me. I am trying to recreate the same environment for the el34s.
I may try the KT77 tubes down the road, but I want to concentrate on the 88 and 34 shootout for the time being.
After I get the speakers aligned and the foam absortion set up, I think I will be in a better position to judge.
Hello again.
I just swapped the new el34l's into the amp about 15 minutes ago. I am initially setting the bias at 110mv for the time being. I will let them burn in for a few days and then check to see if the voltage had drifted at all.
By the way.... I blew the main fuse on the Jadis before I had enough time to read the voltages with the new tubes in. I set the pots to fully clockwise after replacing fuse and then slowly calibrated back up to 120mv just to get the feel of the voltage potential problems in this range and to make sure the tubes wouldn't blow the new fuse.
So I have a doctor appointment at 2:00 and plan on listening to some music tonight.
I am pretty excited to hear these new tubes break in. I am playing them pretty softly right now.
I have to run now. Thanks again.
I have about 120 hours on the new JJ tubes.
Trelia, much thanks. I love the tubes. The soundstage seems to be much deeper and detailed. I am going to enjoy it for awhile before I try any other rolling.
And thank you, Mechans, for your valued input. This has been a very positive change in the sound of the JOR.
The tubes are excellent. I am really very happy with them. The only thing wrong is some crackling in the right channel during warm up. I am going to call Tube Depot and talk with them today.
Otherwise, I am am just letting the music take me away again. When the relaxation reaches the point of bringing you into the 'other worldliness zone", you know you are back in the right ballpark again.
Right now, I am finding the detail as clear and crisp as ever, the air between the instuments and voices is very obvious and the highs and lows are not lacking in any area. I still feel them breaking in and massaging the music into its final places though. They are definitely at least as good as the Gold Lion KT88s that I originally had in the system. The TungSol 12ax7's are in with the JJ's right now too.
I may try rolling and tweaking a little more in the future, but for right now, I am just going to enjoy the heck out of what I have.
Thanks guys.
I just had one of my audio buddies stop by to listen to the new tubes. I walked away to let him get into the music. Hr listened to Lee Ritenour first. He got so excited and emotional while listening to it that he just wanted to describe his experience to me. He listened to Dave Koz and Boney James before he had to leave.
He was amazed at the positioning, clarity, fast, clear bass and everything else he heard. He wants to come back this weekend with some of his reference music.
It was a good afternoon for both of us.
I am truly amazed at the difference that the JJ EL34L tubes have made. And at half the price of the KT88's I had been buying also.
Thanks again.
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