[1000a]

http://www.tubedepot.com/nos-6ca7-mullard-xf1.html

 

[1000a]

Seriously has anyone ever heard these things?  Also for the NOS gang, I know squat.

Are there any reasonable 25. per tube NOS or other 12ax7, 12at7 that would offer me a pretty serious sound improvement over Swetlanas of the same model #?

thanks in advance,

[Audiovista]

Regarding advice about NOS tubes, contact AJ at Tubemonger, I'm sure he can help you.
Boris

[1000a]

thanks Boris

[Bill Baker]

Choosing tubes, especially NOS, is a very subjective subject. You can receive 100 different opinions and they are just that....... the opinions (preferences) of others.

 NOS tube rolling can become very expensive if you are taking the opinions of others. Rather than simply getting recommendations, I would look for those who have done comparisons of different tubes within a product similar (if not the same) as what you own. Even then, you must be able to read between the lines.

 I receive feedback on a regular basis from those who have experimented with different tubes in my products and every opinion (preference) is different. It comes down to personal preferences and taste.

 Just looking out!

[1000a]

thanks Bill

[richidoo]

There has been some welcome technical progress in the EL34 type in the last few years, due to the huge demand for them in guitar amps. John Lennon used them and made the sound famous, as did many many other guitar heros on famous solos. It can be a rich ballsy sound, but hifi demands are quite different than guitars which want as much distortion as possible, which stereos want the least. My amps require 8 of them, so I spent a whole week reading the opinions and researching them, and contacting a lot of the distributors for their recommendations.

Among the best quality EL34s in new production:
SED winged C EL-34
Groove Tubes E34LS (made by JJ, not same as JJ EL34)
JJ KT-77
EH

There were some other tubes called "the best I ever heard..." but these listed were consistently mentioned above any others. Some have suggested that the KT77 are better than NOS Mullards, but in my amp, the GT tubes were better than the KT77. The GT tube designer also designed my amps, so no wonder they are preferred, so I am sticking with the OEM tubes. Like Bill said, you just gotta bite the bullet and try a few different ones to see what you like. If you want some quality brands to consider, the above might be a good starting place. Often the OEM tubes are best, since they were selected by the designer for a number of reasons. Rolling is fun, and occasionally you hit the jackpot, but it can be expensive and feels like gambling. Thrilling, maybe addictive for some people. Uh-oh! Flames coming!

As for 12AT7, most tube equipment designers think this tube is not a great audio tube due to its non-linearity compared to other more popular tubes. Famous NOS versions are easily available. AC member "SY" tested a bunch of brands of 12AT7 very thoroughly, and found the new JJ 12AT7 superior to all others in THD and harmonic distribution. He said alot of them, even the famous NOS versions have excessive 5th order harmonics, which is much lower in JJ. I bought a pair to replace the EH splitter inputs that came with my amps and heard a very noticable improvement in smoothness and a lighter, more glistening approach (damn words!) I assume it got even a little better with break in, but didn't really notice that. I got the gold pins, matched and triode balanced, from tube depot, FWIW. You might think they suck in your amp, but that's my .02 

Rich

[JoshK]

As for 12AT7, most tube equipment designers think this tube is not a great audio tube due to its non-linearity compared to other more popular tubes. Famous NOS versions are easily available. AC member "SY" tested a bunch of brands of 12AT7 very thoroughly, and found the new JJ 12AT7 superior to all others in THD and harmonic distribution. He said alot of them, even the famous NOS versions have excessive 5th order harmonics, which is much lower in JJ. I bought a pair to replace the EH splitter inputs that came with my amps and heard a very noticable improvement in smoothness and a lighter, more glistening approach (damn words!) I assume it got even a little better with break in, but didn't really notice that. I got the gold pins, matched and triode balanced, from tube depot, FWIW. You might think they suck in your amp, but that's my .02 

Rich

I was agreeing with you up until the point about 12AT7's being non-linear. Its true many NOS versions might have high distortion, but the 12AT7 is far more linear and lower in distortion than the 12AU7 or the 12AX7.  I believe it is even more linear than the 6922 or 6DJ8, so already its more linear than most popular audio tubes.  It is shamed by the 6SN7 however.

[richidoo]

Hmm, interesting. I respect your opinion and will keep my eyes open for more info corroborating your view. I am using them in my system and very happy with the circuits that use them Anyway, the JJ version is a good quality tube, maybe worth a swap.
Rich

[JoshK]

Well of course my knowledge is second hand, but the only people I've seen poo-poo the 12AT7 are usually on AA and usually have never tested them themselves, so I don't know where they get their info.   SY (Stuart) and quite a number of other experiences DIY'ers who test themselves have shown lots of evidence that the 12AT7 is multiples more linear and lower distortion than the other 12A_7s. It also has higher transconductance (gm) which makes it a better driver and phase splitter than either the other two.

[Bill Baker]

I have to agree with you on this one Josh. This is why you see so many designs using the 12AT7 as a driver/phase splitter. I have also found that the 12AT7 usually provides better results when it is used in substitution for a 12AX7 as an input tube.

 The only other tube I would prefer (depending of course on the circuit requirements) is the 6SN7 or 12SN7. This is only a personal preference based on my experience with this tube.

[alotaklipsch]

Seriously has anyone ever heard these things?  Also for the NOS gang, I know squat.

Are there any reasonable 25. per tube NOS or other 12ax7, 12at7 that would offer me a pretty serious sound improvement over Swetlanas of the same model #?

thanks in advance,

Yes, I use either the big base Xf1's or metal base, matched quads in my dodd 120's.  I have NEVER lost a tube, t wear and tear, and they are amazingly musical.  If your system is transparent enough, to hear any change ie: pc, interconnect, tube, et.  Then they make a huge difference.  But, nt until you get your system to that level.

[1000a]

I have to agree with you on this one Josh. This is why you see so many designs using the 12AT7 as a driver/phase splitter. I have also found that the 12AT7 usually provides better results when it is used in substitution for a 12AX7 as an input tube.

 The only other tube I would prefer (depending of course on the circuit requirements) is the 6SN7 or 12SN7. This is only a personal preference based on my experience with this tube.

In the Jolida 1000a stock form can I use 12AT7s in place of the (2) 12AX7s?
I have read the gain is lower on them vs the 12AX7?  If so I would be replacing the (2) driver tubes and the (2) pre-amp tubes all at the same time.  Are the 6SN7 or 12SN7 another option I can try with this amp?   Thanks in advance,

[1000a]

There has been some welcome technical progress in the EL34 type in the last few years, due to the huge demand for them in guitar amps. John Lennon used them and made the sound famous, as did many many other guitar heros on famous solos. It can be a rich ballsy sound, but hifi demands are quite different than guitars which want as much distortion as possible, which stereos want the least. My amps require 8 of them, so I spent a whole week reading the opinions and researching them, and contacting a lot of the distributors for their recommendations.

Among the best quality EL34s in new production:
SED winged C EL-34
Groove Tubes E34LS (made by JJ, not same as JJ EL34)
JJ KT-77
EH

There were some other tubes called "the best I ever heard..." but these listed were consistently mentioned above any others. Some have suggested that the KT77 are better than NOS Mullards, but in my amp, the GT tubes were better than the KT77. The GT tube designer also designed my amps, so no wonder they are preferred, so I am sticking with the OEM tubes. Like Bill said, you just gotta bite the bullet and try a few different ones to see what you like. If you want some quality brands to consider, the above might be a good starting place. Often the OEM tubes are best, since they were selected by the designer for a number of reasons. Rolling is fun, and occasionally you hit the jackpot, but it can be expensive and feels like gambling. Thrilling, maybe addictive for some people. Uh-oh! Flames coming!

As for 12AT7, most tube equipment designers think this tube is not a great audio tube due to its non-linearity compared to other more popular tubes. Famous NOS versions are easily available. AC member "SY" tested a bunch of brands of 12AT7 very thoroughly, and found the new JJ 12AT7 superior to all others in THD and harmonic distribution. He said alot of them, even the famous NOS versions have excessive 5th order harmonics, which is much lower in JJ. I bought a pair to replace the EH splitter inputs that came with my amps and heard a very noticable improvement in smoothness and a lighter, more glistening approach (damn words!) I assume it got even a little better with break in, but didn't really notice that. I got the gold pins, matched and triode balanced, from tube depot, FWIW. You might think they suck in your amp, but that's my .02 

Rich

Thanks for helping out.

OK the winged "C" thing is a pain, my first set of EL34s where Svetlanas and had a winged "C" on the tube and did not say Svetlana on the tube .  My current set in fact were ordered as SED winged "C" so that is my current power tube, I have never had any complaints with them in fact like them a lot, but you know hmm........what else they got?  I'll probably roll the dice next time try the GTs or even the KT77.  It seems Nel's TNT article on the 302 had comments on KT77.

As for the front end tubes I am definitly going to give the JJ/Telsa 12AT7s a go  (currently using EH there).  What is the benifit of gold pins?  Hoping Bill will chime in, I am hoping to get the 12AX7s out of the chain.

thanks again

[richidoo]

Thanks Josh and Bill for setting my assumptions on a better course. I probably got the impression from AA, or some experts on the "internet." I understand that originally 12AT7 was not intended for audio, but for radar or some other industrial app.  12AU7 was intended as an audio tube to improve on AT as a lower gain 12AX7?

1000a, I got the gold pins because they are much prettier. haha Steel pins have identicle innards, so pragmatists would say no difference. Gold won't oxidize, better conductor than steel, although the pin sockets are steel, so whatever.

Svetlana vs SED?

The GTs are very dynamic, and designed to be more powerful than standard spec EL34, 5 more watts. Picture the ultimate rock guitar sound. Bass is very strong and punchy. It is a different sound, very exciting, not laid back. But there I go again, that is the sound of my amp that is exciting with these tubes. Yours might sound like shit.  I don't listen to a lot of rock, mostly big classical and combo jazz, but I like the power and super direct feel. My amp has a custom output transformer made specifically for these GT tubes. Maybe talk with your amp designer. He chose certain tubes for production where he needs 500 good tubes a year. If he only needed a quartet he might prefer something else and might tell you what might be worth a try.
Rich

[JoshK]

In the Jolida 1000a stock form can I use 12AT7s in place of the (2) 12AX7s?

Maybe...I don't know the circuit too well off hand.  You aren't going to blow anything up by trying though, you would just get suboptimal results if it didn't work out.  IIRC, the operating points are pretty close to one another, and of course the pinout is the same. 

I have read the gain is lower on them vs the 12AX7?

This is a bit chicken/egg as I see it.  The 12AX7 has higher gain, but lower linearity, requiring more feedback, which needs more gain.  If you are designing a pentode output stage and know you are going to have to wrap a gNFB loop around it, you may need the extra gain.  Then again, you may not. 

If so I would be replacing the (2) driver tubes and the (2) pre-amp tubes all at the same time. 

Are the 2 12ax7's in the preamp part of the phono stage?  If so, don't replace those.  Phono stages are very critically tuned to the specific tube's parameters and aren't as flexible and robust stages for rolling different tubes.  There you need that gain and the RIAA circuit is optimized for its Rp and current output. 

Are the 6SN7 or 12SN7 another option I can try with this amp?   Thanks in advance,

Totally different beast.  These use an octal socket (larger 8 pin instead of small 9pin).  The circuit really needs some redesign to use these in lieu of 12a_7s. 

[FEB2March]

Josh, love your pic 

[1000a]

thanks guys,

it certainly seems worth a shot to try the 12at7s in place of the 12ax7s, I will check with amp designer first.

I probably should not have used the term front end , I meant front end of Integated amp (w no phono stage). 

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

[JoshK]

Yes, then you should be able to replace both preamp and drivers with 12at7's.   If I knew how much filament current you had in reserve I can recommend some other drivers that will blow your mind, or I'd think it would.  Basically, the JJ ECC99, any number of 12BH7's or 12BY7's would work in driver (but not neccesarily preamp, like the 12at7 would).   If you shared the schematic with me, I could help figure all that out, assuming it was detailed enough. Otherwise, if the manuf is helpful, then that will work too.

I think the schematic is floating around the web somewhere...

[Bill Baker]

Hi Josh,
 I do agree there are other input/drivers that are preferred over the 12AX & 12AT7 variations but not an easy task with this amp.
 You are dealing with an amp that has the 9 pin tube sockets mounted to a circuit board so swapping in octal sockets is no easy task. Not to mention the circuit changes that would have to be made. I know......I've done (tried) it.

 You can use variations of the 12AX7 for the input tubes right down to the 12AU7. The problem here is that the amps circuit is not optomized for the 12AU7 and causes increased distortion when pushed too hard.

 The circuit for the JD1000 is the same as the 302/502 amps with only additional circuitry for the extra output tubes. I do prefer the 12AU7 over the AX7. This is why I redesigned the circuit of our Bella Extreme 3205 MK II amplifiers (based on the Jolida "A" series 302/502 chassis) and optomized it for the 12AU7. While you can sometimes use the 12AU7 in place of the AX7, you CANNOT substitute the AX7 for the AU7 due to differences in opperating points.

 I do run one of my original 3205 amps, before the MK II circuit change, with 12AU7 input tubes as I still prefer the sound.

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). 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.