[JoshK]

normal confiquration is:
(2) 12at7s for pre amp
(2) 12ax7s for power drivers.

 Sorry dude, you have this backwards.  The 12AX7 tubes are the input tubes (two center tubes) while the 12AT7s are the driver/splitter tubes. (outside tubes).

I kinda thought that might be the case, but wasnt' going to argue.  The 12ax7's aren't great for a driver, imo (based on specs).  The 12at7 is more natural here.  Designers usually use the 12ax7 for gain because of its high gain. 

If you have these reversed, this could cause damage to the amp's circuitry if left in place too long as the 12AX7 is too "hot" to be used as a driver.

You lost me here.  So I take it the driver is configured as a grounded cathode, not a cathode follower.  I would have thought it would have been a CF driver stage.  As a grounded cathode, that is a hella lot of gain!  Holy smokes.  That is a lot of feedback too unless the amp is ultra sensitive!   I guess I shouldn't have spoken based on assumption.   I had seen a lot of Jolida and ASL amp schematics and pretty much thought they all followed variations on the same theme.  As it sounds, it is more of a McIntosh style input/driver stage. 

[1000a]

Thanks to all you guys for taking the time to help me.  Sorry to confuse, I had writtian the config. in my notebook correctly then posted config from memory-    Yes, I did install them correctly though. 2 pcs. 12AX7 pre-amplifier(input) & 2 pcs. 12AT7 power drivers(driver). 

Due to design constraints (the driver tubes stay 12at7) and my choices are:
A-input tubes can be changed to:  12at7 (should be an improvement)
B-input tubes can be changed to:  12au7 (may be a better improvement, but I might suffer some distortion if I push amp to hard)

Is the volume at 2:00pm (max I go) to hard = audible distortion?  Too many variables to answer correct?  Thanks in advance,

[1000a]

OK (this makes sense for the brand) what I am after.
 
A- Currently I have gained tons of detail, dynamics, bass def., air, stage, image spacing and without losing body (so I am definitly making progress) but I lost some of the original midrange beauty and liquidity I had before.

B-So what I am after with the input & or driver tube change is more warmth, tube euphoria, liquid, smooth, mid range richness and so on.

Caveat:  I do not want to sacrifice much of A to regain some of B.  Do you guys have any suggestions, in that light.  The current input & driver tubes are EH.  Maybe I only want to change the input or the driver tubes.  Don’t know.

I am eyeing RCA black plate, Sylvania grey plate in either 12au7 or 12at7?  Sorry for so many endless questions I got a lot to learn yet.    Thanks again.

It should be noted the power tubes are SED EL34s, my DAC is an upsampler but I do not know if that feature is working with the SB3, the lights on the DAC do not indicate it is up-sampling.  The next DAC will be a NOS unit (w or without a tube).

[richidoo]

Try comparing JJ 12AT7s to your EH and any vintage drivers you might try. You might be surprised! The SED EL34s are great tube. Since you said you are new to tubes, do you know how to bias your power tubes? That has a big effect. Bias will change during break in so check it often when tube swapping. Be careful not to cook tubes from too much bias due to setting of previous tube. If you stick to EL34 type shouldn't be a problem, but with rare NOS tubes, you wanna be a little more careful ($). You can always turn it down a bit before swapping, more work, but safer. If your amp does not have individual tube bias, you need to buy them well matched to avoid PP crossover distortion which is no fault of the tube, but it will sound that way... Buy from a dealer that can match them well.
Rich

[ZLS]

   I don't know if this is the right thread to ask this question, if not I apologize. 
    I have a rebuilt Eico preamplifier which line stage consists of two 12AX7 tubes.  I have two questions,
1. Can I drop in two 12AT7's?
2. What would I gain or lose? 

                                 Thank You

[Bill Baker]

 I don't know how the circuit would handle the 12AT7 (not familiar with the piece) but the 12AT7 has a bit less gain than the AX7.

 Gain Factors - Mu

12AX7 - 100
12AT7 - 70
12AU7 - 19

[1000a]

OK Rich,  I ordered 4 12at7 JJs, I look forward to giving them their debut next week.  Ordered matched sections, matched pairs.  I can't adj. bias on either the input or driver tubes.  I can bias the power tubes and have, and will re-due the bias next week when I replace the EH w the JJs. I hate doing it so I'm sure its not at optimum, I probably need to check it more often.

Between now and then I am going to assume there is RFI and EMI in my system with all this magnet wire I have, although I do not hear anything blatant, it could be subtlety affecting the sound and me not know it.  Thanks so much, I'll post my findings with the JJs IMS next week.

[Bill Baker]

I hate doing it so I'm sure its not at optimum, I probably need to check it more often.

 Just curious when you biasd the tubes last? Did you replace any tubes and not bias all of them? Tubes that are biased higher than their proper setting can also produce noise in the system. I know it is a bit more difficult in the JD1000 but I would definately check them periodically.
 Whenever you install new tubes, you should always turn the bias pots all the way down before installing the tubes. You never know what the new tubes' specifications are. Then go through and rebias all the power tubes. I would recommend a bias between 35mV-37mV.

[richidoo]

Not to worry about the wires making RF. What RF they emit is low intensity, unmeasurable an inch away, and within the audio band where they will not be noticed even if they could get to a sensitive circuit. All your components are in steel boxes for a reason, it sinks RF to ground! No worries.

I hope you like the JJs. I'd be curious what you think.

Yeah, tubes are a pain in the butt sometimes, but they have their rewards. Watching the bias is just one of the many rituals we pay to the great thermionic spirit for our continuing listening pleasure.  I am obsessive so I check mine every week when new tubes are in, then about every other month after they settle down. I can hear a difference if they are not pretty darn close. In push pull topology, the power tubes work in pairs, and are handling off the output signal to each other each 1/2 cycle. The point at which they hand it off is called crossover. Mismatched bias between the two tubes sharing the signal will make the handoff less smooth and produce audible crossover distortion. Did I get that right Bill? When you have a pair of tubes sharing one bias adjustor, they should be well matched to lower the crossover distortion they produce when working together. Unfortunately as tubes burn in, their ideal bias points may diverge from what they were when new. No biggie, especially with good stable tubes like your SEDs which are very consistent and once broken in hold rock solid bias. But, since the point of using a high end amp is to achieve lower distortion, might as well get your money's worth and adjust that bias.   hehe

Input and driver tubes operate in class A (usually) so there is no push pull, and no bias adjustment needed.

Rich

[1000a]

I hate doing it so I'm sure its not at optimum, I probably need to check it more often.

 Just curious when you biased the tubes last? Did you replace any tubes and not bias all of them? Tubes that are biased higher than their proper setting can also produce noise in the system. I know it is a bit more difficult in the JD1000 but I would definitely check them periodically.
 Whenever you install new tubes, you should always turn the bias pots all the way down before installing the tubes. You never know what the new tubes' specifications are. Then go through and re bias all the power tubes. I would recommend a bias between 35mV-37mV.

last bias 1 yr when I installed 8 new p-tubes, biased all of them, I do turn them all to o when installing new one(s), I have been setting them @ 40 mV per jolida (I will change that to 35-37)

If you guys can offer me tips on a more efficient bias, less stressed, less hassled procedure that would be really helpful, I could probably get it to a simple ritual rather than an oh-sh I gotta fix my amp-a tube went south, go get the jolida manual and X every T.

Turning the pots and watching the meter is really not the problem, its the danger that worries me.  So first and foremost I guess I need a grounding belt? (radio shack?)?  That would relieve that stress and anxiety, which should speed me up.  I use a very bright light so that helps and I place a board across the chassis front to back to hold the meter, a plastic handled screw driver w electrical tape wrapped around & running the length almost to the tip (I did once inadvertently touch the transformer w the screw driver tip- could that not kill me?-or am I miss informed).  This next session the amp will be sitting on the floor.

I do see the need to do a bias check - adj now (off could be costing me noise & so on) otherwise my comparison of the EH vs JJ will be unfair and unhelpful to me.
photo included for Rich's perspective, the pots sit between the transformers and last row of El34s - close to the edge of the circuit board.

[Bill Baker]

Hello 1000, while you are unlikely to get killed or even hurt if the screwdriver slips in this amp, it could wake you up and/or damage the amp if you short out one of the resistors next to the pot. Most likely, you would take out a fuse first.
 Radio Schack carries long handled (about 10") plastic screwdrivers which are very good for this application. I think ther are about $2.
 If it has been a year since yo last biased this amp, I can almost guarentee they are way out and potentially causing you some noise.
 Let us know what you find out. I would love to get to the bottom of this isssue.

[richidoo]

Wow, what a beautiful amp. Nice clean design. Looks like you have individual bias pots for each tube  I like all those tube dampers too. I gotta try that on mine sometime.

You will find that your bias settings are way off unless you biased them again after tube breakin was complete. You will like what the bias adjust does for you. I can also understand why you started this tube swapping post!! The SEDs are a great tube. Spend some time with those running properly and see if you still desire a change.

Your concern about being electrocuted is well founded, because you have high voltage DC in there, and there are leads to the bias resistors close to the pot screw. Maybe pick up a plastic pot adjustment screw driver. Using a taped screwdriver sounds smart. The tape would serve to prevent your fingers from touching the metal screwdriver shaft at the time of contact with a high voltage lead. If you hold the screwdriver at the top end of the insulator handle you have nothing to fear except dropping it in there, and even then a fuse will shut it down. I don't know if a grounding belt will help you, I would guess it would make the shock worse by forcing it through your body. You are not worried about static shock with tubes. Wood board on top also sounds helpful. Are the test probe connections easy? Especially the ground connection should be make as easy as possible and idiotproof, maybe alligator clip or whatever so you don't have to look at it or worry about it when you move the other probe around. 

When you say 40mv, you mean 40ma? The bias is current, but is often measured in volts across a resistor according to ohm's law. I set my bias in voltage to 300mv to achieve a 30ma bias current across a 10ohm resistor. Maybe you set voltage to 40mv to achieve 40ma bias? Obviously you have the manual for reference.

From what I have read, the higher the output tube bias, the better some designs will sound, but not always. And the cost is shorter life from the tubes because they will run a lot hotter. Keep it in a cool well ventilated spot. Maybe run an AC duct inside it haha Bill knows how to make an amp sound great, one of the best designers in the country. His advice on bias is valuable, so experiment and see what you like between 35 and 40ma. Lower bias won't hurt anything, except maybe your ears. To me very low bias sounds terrible.

As for the bother, once you start doing it it will become second nature and you will feel like a cool dude fixing your tube amp. It is not dangerous if you know what you're doing, know what to avoid (touching those resistor leads with your fingers on a metal screwdriver shaft), and work when you are fresh and in the mood. Have fun!

PS = In researching preamps this week I see a lot of very well respected designers using 12AT7 in their designs, VTL, AVA, Manley, obviously Jolida. I think my negative bias against it is cured.  Thanks
Rich

[1000a]

OK, settings before adj. left to right. tube3-tube12

.042/.043/.039/.040/.042/.040/.041/.042 (DCV,2v)

.399/.412/.372/.380/.403/.381/.388/.399 ((DCA, 2mA)

adj w (DCV,2v) to .037 across the board.

which is a more accurate reading the DCV,2v or DCA,2ma (it seems the voltmeter readings are 2 digits apart everytime, at least its linear anyway.

will report back on sound changes later, easier to do on the floor than on a rack, anxiety is far worse than the simple project-will redue when I get pre tubes.  At that point do I set all the power tubes to 0 and redue them or just check em and adj?  Thanks a mil, went very smooth-double checked em cause sometimes once I do them all I come back across and find one off, don't know why.  Thanks again.

[1000a]

Wow, what a beautiful amp. Nice clean design. Looks like you have individual bias pots for each tube   I like all those tube dampers too. I gotta try that on mine sometime.

Rich

Thanks so much, I loved the changes the tube dampers made in my system, really incredible across the board detail,staging, imaging, air, impact on so on.    I can not be enthusiastic enough about the improvements.  Best bang 150. I ever spent on my stereo, period. 

I should have posted my findings with them, what happens is a couple of weeks into an improvement and it just gets absorbed into the sum (total presentation) of the parts for me.  Although the good news here is I am thinking differently about changes in the system, using a more holistic approach with present gear as opposed to this one individual piece will blow my mind.

In fact Bill (Response Audio) years back had suggested I try them before putting any money into modding my amp.  Being a kinda come and go audio obsessed person, I did not try them until I purchased an SB3, which kicked in my whole current improvement trip which has been a blast.

I got mine at Herbie's Audio (I only can speak for the Halos), can't go wrong 90 day no questions asked return policy.  I wasn't 2 minutes into the listening session they were not going back, period!  Excellent mucho recomendo, don't know why I hesitated, so many I respect had nothing put praise for them.  I probably got obsessed with something else.

give em a whirl, can't lose

PS   The only thing that might compete for bang for the $$ is my DIY projects with magnet wire, that I have easily spent 150. on only to find out there is a such thing as Teflon covered magwire (2.2 dielectric constant) vs Polymide magwire (2.8 dielectric constant).  What I have been using is a combo of enamels so the dielectric constant I am dealing with is far higher than 2.8 probably 3.8+.  The good news is its incredible so I can't wait to get the Teflon stuff and start all over.  I have not perfected the designs so it was all grist for the mill and another improvement to look forward to.

I shall not purchase a better amp until I have learned how to garner everything out of my present system through research and effort.  This disciplined approach should teach me allot and serve me very well (and its extremely rewarding & enlightening) when I move up a notch.

[richidoo]

Hey, no fair! You pretend to be a neophyte and then find out you are a seasoned tweeker! haha  Hey you tried the JJ inputs, so I will try the Herbie dampers. Hell I thought they were stock with the Jolida. Thanks for the mini review. My tubes do ring, and I don't have particularly good vibration isolation rack. WEEZ recommended the Mapleshade rubber/cork isolators for TTs, I might try some of those sometime too.

Good job on the biasing. You will find some tubes go off when you go back and check because you are adjusting the current consumed by the other tubes, which is all drawn from same supply. Changing current consumption on one tube effects the other 7. 2 laps around is close enough, .1 ma accuracy is overkill, unless you are one of those.... hehe  Also, the manual probably told you to apply a mute signal so no signal is playing, that will change the bias reading as current is delivered to speakers.

Off to Herbie's...
Seeya

[1000a]

You pretend to be a neophyte and then find out you are a seasoned tweeker!

Seasoned tweeker that's funny, with all the Enlightened Yodas on audio circle I feel like I crawled out of the primordial ooze.

I don't have particularly good vibration isolation rack. WEEZ recommended the Mapleshade rubber/cork isolators for TTs, I might try some of those sometime too.

Also worth a try for vibration-isolation are the vibrapods, $6 a pod highly rated and cheap.  I like the results I get from them under my TT and amp, using the sandwich technique.  To be fair I have never tried metal or wooden points.  From what I understand, the points direct the vibration in a componet to a different place and softer solutions, isolate the componet from other outside vibrations getting into the component.  Pretty sure I got this right, 2 schools - some people use both in different situations.

google em, also see TNT audio (great not for profit-no ads website) review of them.

[richidoo]

Here is an interesting read about vibration isolation/damping. See the articles on left pane, especially white paper.

What kind of Halos are you using? It is kinda confusing to get a grip on all the materials and choices, plus looks like new stuff coming out next week. Just buy the most expensive type I can afford?

[1000a]

of the 3 types they currently have I got from first page descriptions at the top:

old name                                                   
white teflon (using for input and pre tubes)
nickel alloy (using for power tubes) 

[Steve]

Hi gentlemen,

     I have to respectfully disagree on the 12AT7 being more linear, esp against the 12AX7, 12AU7, and even the 6dj8/6922/E88cc tubes in lower signal service. In my measurements, and inspecting the curves, years ago, the 12AT7 had very high distortion. I found it very unacceptable.

Here is a picture of the curves. Notice the odd spacing.
http://www.mif.pg.gda.pl/homepages/frank/sheets/087/1/12AT7WA.pdf

Now a typical 6dj8 (not JJ curves which is a more linear tube).
http://www.mclink.it/com/audiomatica/tubes/6dj8.htm

Now a typical 6sn7wtb tube.
http://www.nj7p.org/Tube4.php?tube=6SN7GTB

Notice the 12AT7 curves are no where near the other tubes. (For newbies, check the spacing between the lines. The spacing varies.)

At lower signal levels (say 5 volts rms) the JJ E88cc (european number) is much much lower in distortion than any NOS 6dj8/12AX7, 12AU7 and 6SN7 tube made.

Anyway, if JJ did to the 12AT7 what they did to their E88cc, it is probably the lowest distortion 12AT7 made in any era.

Take care.

[1000a]

OK Rich, - I just hung up with Steve Herbelin (Herbie's Audio-owner ), long 30+min conversation extremely helpful, tons of integity (just like Bill @ Response Audio ). Steve's deepth of knowledge of tube audio is stagering at least to me.   He is going to send me some titanium rings for the nickel alloy rings that are on my dampers on the EL34s. That is the basic change to the primary damper of his product line.

You should check out the FAQ page and call him if you need to. If you call him just tell him what you would desire in your ststem he would recomend based on that, otherwize I'd start with my suggestions below, keeping it neutral and getting all the detail you can. Heres my understanding of the newer products:

1-blackbery very good at extracting much musical detail from small tubes (preamp stuff)
I'd start with these for pre stuff.
2-ultrasonic halo (what I got for my EL34) I'd start with these for power tubes.

skip the teflon not as musical as the others.
blackbery only for small tubes very musical, lots of detail
ultrasonic halo for all tubes -the most neutral for primary tubes.
peek dampers- more body, less glare- only do these to the power tubes after

you have tried either the peeks (more body less glare) and or ultrasonics (less detail than blackbery still neutral) on the input and driver tubes.  far less $$ changes here can easly do it.   I hope this makes sense and is helpful.