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 16 responses by trelja

The official bias settings for whatever tubes you use in the JOR are 90 - 120 mV, with 110 mV considered the preferred target.

As you noticed, at 10 mV, there is hardly any current flowing through the tube, and to draw an analogy with water, the valve (as the British call them, and a better and more meaningful name) is just about fully shut.

I like both the KT88 and EL34 in the JOR, but my preference is the latter. Of course, your tastes may differ.

Was hoping to see you in NYC, Doctor. Had a great time at the show. As you said, this new world of not being able to contact people makes things hard on everyone.
I think you should be fine with the Mullards, Mattzack2.

The one thing I would say is to not put more than one variable in play at a time (Scientific Method), so that you can accurately assess the effect of each change. In other words, you should go back to your old 12AX7 for now to understand what the Mullard EL34 are providing. As the JOR employs the classic Dynaco (MKII, MKIII, ST70) circuit, the driver tubes play a pretty important role. Once you have a good handle (100 hours) on the Mullards, go ahead and reinstall the TungSol 12AX7. If things don't work out and you don't like the Mullards, perhaps I could purchase the from you?

The JJ E34L likely took a half day before I began to notice them, and a weekend (daytime, only) to really settle in. My speakers are pretty efficient, what are you driving with the JOR? Also, please remember to recheck/reset the bias.

Yes, same e-mail address, Doctor - [email protected] and [email protected] I've tried writing to you over the past year or so, but have had all my attempts bounce back to me. The NYC Show was great. In my most conservative estimation, easily five times the headcount of last year, with a much better venue. I'm sure as much of a success as turned out did this year, there should be substantial growth for next year's show.
Glad to hear the EL34 are improving. Here's hoping they get to where you hope.

The speakers I've paired up most with my JOR are Coincident, about 91 db/W. I've also had the Gemme Tantos - the first iteration, where the cabinetry was done in Canada, not China, and they are not especially easy to drive. Yes, you can certainly play and perhaps even like them. But I found they more come alive with emphatic solid state amplification.

Please keep us posted as to what you find over the course of the weekend.

For what it's worth, the current production triple mica Shuguang 12AX7B are the sleeper of this tube. The Doctor (Mechans) and I confirmed this several years ago to our surprise. We then hosted a tube shootout where they bested some very highly regarded old 12AX7 variants, and finished in the top three overall.
Doctor, did you find the TungSol 12AX7 superior to the Shuguang 12AX7B? If so, that's quite a statement.
Doctor, I would say you have more knowledge in terms of the 12AX7 and 5751 than I.

While I do feel the Sylvania 5751 Grey Plates have a bit more thunder down under, as you had also thoroughly evaluated the GE 5 Star and RCA variants, your insight and overall perspective surely betters mine.

Regarding the Shuguangs, I find they do not lack in the low end. Previous to finding them, there was no production 12AX7 that I felt held up against the tubes of yore. But outside of the JOR, where the lower gain potentially becomes an issue, I'll still take the 5751.

Care to provide an update on how break in left things, Mattzack2? How do you find the Mullard EL34 in comparison to your Gold Lion KT88?
Mattzack2, your experience perfectly mirrors my experience when it comes to bias. As I said, as you increase the current flow in the output tube, outside of tube life, EVERYTHING gets better.

At this point, I don't want to encourage you to stray far from the recommended values. But I will say that if one calculates the JOR's plate current in the traditional manner, 120 mV divided by the 5.62 Ohm bias resistor would yield 21.35 mA, an incredibly (low) cold figure.

In comparison, my Dynaco ST70, which uses the same circuit, aims for a bias of 50 mA. The rule of thumb in the guitar industry shoots for 70% of maximum (25 watts for an EL34) plate dissipation, which obviously comes out to 17.5 watts. Though so many maintain the Dynaco's biased way too hot (415V B+ X 50 mA = 20.75 watts), I argue that after all these years you find so many with their original Mullard EL34, the assertion proves false. Figuring on the JOR's approximate 450V B+, at 21.35 mA, we're only at 9.6 watts, not even 50%.

I did send an e-mail to Patrick on Friday, but as of yet, have not received his reply. He's usually very prompt in these matters. We'll hope to hear from him soon. Again, I want to get his answer on the matter before saying to aim higher, as Jadis does employ a novel twist on connection to the output transformer, and the usual way of calculating these things might be very, very wrong. But, there's no need to back off from 120mV.
No, I think that is Joe Abrams of Equus Audio. I remember his banner ads here on Audiogon.

Please let us know how the amp sounds at 150 mV, and whether you feel the Mullard EL34 should stay.
The JJ that I liked in this amp are the E34L, which do have a much different sound than their EL34.

The JJ EL34 is more typical of EL34 sound, with an evenness of hand from top to bottom. The E34L give up some of the bottom end for a midrange that can be otherworldly in the right setup.
Mattzack2, thankfully, I've received two replies from Jadis. Both, from principals of the company.

The JOR conforms to the traditional means of calculating bias current. So, the calculations above ARE correct.

Patrick used 150 mV and stated, "the sound will be better but the tubes are not so secure." 150 mV / 5.62 would mean 27 mA of output tube current, still very easy on the tubes.

As I have maintained of late, I don't want to say much here in public regarding my personal experience, as it's prudent to have folks stay within the manufacturer's recommendation.
So nice to hear things are working out, Mattzack2!

If current bias sits at 120mV, I'd say goose it up to 150mV once the tubes are fully broken-in. Again, 150mV still represents quite a conservative setting. Can't really put a hard and fast figure on break-in time, but for me, it occurs when you are hearing no additional improvement.
So glad to hear your impressions, Mattzack2.

Also, many thanks to you and The Doctor for making this one of the better threads I've been involved with in quite some time. Thank you!
Doctor, can you let me know your e-mail address or send me an e-mail([email protected]), please? I need to talk to you.

Mattzack2, what you and your friend hear from the JOR shows why it has won such a deep level of affection with me. You can get sound out of any amplifier, but to find one which puts music in your house rarely happens. Enjoy!
My apologies for the late reply, just arrived back from our summer vacation.

My JOR uses a 4A/250V fast blow fuse. Personally, I feel a slow blow fuse is always the better way to go in this application.

Doctor, can you let me know your e-mail address, please?
Angelo, if I'm not wrong, I don't think you need to bias a DA-8. My understanding is that this represented the power amplifier section of the DA60, which features a cathode bias topology. EL34/6CA7, KT77, 6550, KT88, KT90, and KT120 should all be plug and play. Of course, you could confirm all of this with Patrick.
If you've reached the 100 hour mark, I think you're now hearing what the tubes are going to do.

"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?"

Well, I've been resisting saying this since the beginning of the thread, as I've seen the pocket protected high-end audio safety police go nuts in a "we're going to DIE!!!" scream whenever anyone suggests going outside of the manufacturer's recommendation. But I have experimented with this, and I have discovered that as with most tube amplifiers if you are interested in sonics, you want to bias the tubes hot (if you are bent on staying within the lines, think 120mV, not 90mV). This was demonstrated most starkly to me by an older gentleman who really knows tube amps, and biases his amplifier to the point where the plates of the tubes begin to glow, then (maybe) backs off a hair. The increase in everything - be it imaging, low end, warmth, and overall musicality is obvious. Of course, tube life suffers. Perhaps, dramatically. It's no concern to him, as he's not on the audiophile train, and uses a tube that no one has interest in, so he would have enough for his grandchildren that he acquired for nothing. But I don't want to suggest anyone try that as standard operating procedure.

Anyway, I can shoot an e-mail off to my friend at Jadis to find out if their novel (pioneered by the Quad II) transformer connection plays any role, or if we can simply figure plate current straightaway from the 5.62 Ohm bias resistor before giving you any hard and fast recommendations in terms of numbers.
Heart attack, Mattzack2?!? WOW, that's serious in the kind of way we almost never get around here. Terrible news, I'm very sorry. I'm amazed how quickly you've gotten back into the game.

I've been in contact with JJ through the past year, and they maintain the blue and red glass have no influence on sonics. Years ago, a person (not at JJ) told me that to the degree the color (red, blue, clear) effect heat dissipation, sonics will follow. For whatever reason, the red tubes don't get imported by those who bring them in, as the blue was what folks went with in this market.

The Doctor and I participated in a JJ E34L vs JJ KT77 vs JJ KT88 shootout in the Jadis DA60 several years back, and drew some pretty stark conclusions from that. I'm not the fan of the JJ KT77 that most are. I've not heard the Gold Lion KT77, but hear good things about them. In the past year, I've purchased JJ EL34 and big bottle 6CA7 tubes. The EL34 have a more even-handed, fuller, richer sound top to bottom than the E34L, filling in that lower end. But, the E34L maintain that glorious midrange. As I just got the 6CA7 two weeks ago, and have been playing with other things of late, I've not yet tried them.

Doctor, the DA30 and DA60 are autobias (cathode bias) as you mentioned. In other words, the bias gets set by a "fixed" resistor connected to the cathode of the output tube, and cannot be adjusted without changing that resistor. The JOR is fixed bias, which means bias is set through a resistor connected to the control grid of the output tube. The term fixed bias is counter-intuitive, as it most often means that resistor is adjustable (potentiometer). A fixed bias amplifier can also employ a fixed resistor inline with the control grid of the output tube, which would not be adjustable without changing that resistor. Beyond having to manually adjust bias or not, cathode and fixed bias differ in their output power and sonic characteristics.