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Here is a link to a site that has a plugin substitute for the 6SJ7.
It is a 9 pin socket mounted on a octal base and comes with a 12AX7. This is supposed to replace the 6SJ7 with a 12AX7.
Does anybody know about this? Also, would anybody know how they did it.
I want to replace my old 6SJ7's in a homebrew amplifier that I have. If only for the fact that 6SJ7's are no longer manufactured.
Check out the link below for this product.http://www.groovetubes.com/product.cfm?Product_ID=1180
Thank you,
Steve Law
Follow Ups:
Generally speaking, all that's required is to connect one section of the 12AX7 to the respective anode-grid-filament pins of the 6SJ7 socket. At $40, you're paying quite a bit for the convenience of a 12AX7 and whatever mechanical contrivance is supplied to physically mate with the octal socket. Given the inferior sonics of the 12AX7, I would suggest that you consider a 6SL7 instead. Rewiring the existing octal socket would allow a 6SL7 to be installed directly. Very little of the existing circuitry, in terms of component values, should require modification. I'll add that plugging in a 12AX7 with existing values is not likely to provide best results, either. If this is a high end amplifier, the conversion to another tube type from the 6SJ7 won't be strictly plug and play, no matter what someone may tell you. Sonics will suffer if the circuit isn't optimized. Incidentally, there are tons of 6SJ7s available on eBay, and audio suppliers generally have a good quantity of NOS at reasonable prices. Angela is currently selling a 10-pack of US-made chrome-dome WGT JANs w/metal base for $50. That's $5 each, probably 1/5 the cost of a 12AX7 of similar quality. Rather than switching to something else, this might be the time to pick up a few bargains for your amp!
6SJ7 INPUT PENTODE TUBES FOR EARLY SOUND EQUIPMENT
1. 6SJ7WGTA JAN Philips/Sylvania '80s N.O.S. One of the best glass enveloped versions of this tube ever made. Rich, full bodied sound, very reliable, quiet too. Replaces troublesome and scarce Western Electric 310A tube in D.I.Y. Model 91 clone amp designs. Also found in some early guitar and PA amps (see the old Ryder PA Manual for numerous examples). This tube also will serve as a good alternative choice to the now hard to find EF86, if you can change over to an octal socket; check your tube manuals and you'll find that the EF86 and 6SJ7WGTA have similar operating characteristics, although I think the 6SJ7 sounds richer. EACH $8.http://www.angela.com/catalog/tubes/Guitar_Tubes.html
I *like* the loudness button!
Hello ,
Very valid points which I totally agree with . Vintage 7F7 are an even better alternative if you have the loctal bases to switch to but keep that a secret ;) Never had any luck at all with 12AX7 which is a shame as I have so many of the damned things !cheers
> > Given the inferior sonics of the 12AX7... > >This is a subjective statement. The experience of quite possibly millions of people directly contradict you.
> This is a subjective statement.I don't care for the sound of the 12AX7. It's a convenient design that saves space, but not as linear as its predecessor.
> The experience of quite possibly millions of people directly contradict you.
Really? How many of those possible millions have you interviewed?
Hi.One's bread can be another's poison. Sonics is subject let alone many DIY design-builds being homebrew toys so often not even up to
any recognised industrial standards.Using such self-esteemed subjective judgement to denounce an established commercial product is a nutshell behaviour, risking
legal consequences should the manufacturers pursue.Save people challenging you, why now substantiate your bad experience with 12AX7 by posting whatever schematics you got problem with as Joel rightly suggested. So that we can learn from your bad experience.
In the past, I've posted numerous successful examples of brandname amps using 12AX7s that have acquired rave appraisals from critics & end-users worldwide alike. Whoever interested can check them up.
Make a wild guess how people had been or still are owners of 50-year-young Dyanco PAS pre-amps, which used 12AX7s throughout. Quite a multitude, right?
Good listening
cheap-Jack
June 14, 2005.
of a crummy design. A 12AU7-ed Foreplay will run circles around it, and the 12AU7 is not at the top of my list for anything.
cheers,
Fred
If we made commercial gear we would have no choice but to use tubes that are in current production and are likely to remain so. I am sure many of the designers of high priced gear that use tubes such as the 12ax7, 12at7, and 6922 would proably choose different tubes for their own personal home built gear. The reason wouldn't be because those forenamed tubes are terrible. Instead it would be because there are a lot of tubes out there on the used market that sound just as good if not better for a fraction of the cost. Given what a top quality NOS 12AX7 sells for why would I even want to consider designing around them? I mean a 100 bucks and up for a single nine pin minature is obscene IMHO. The sound quality is not in keeping with the price. If more folks had the ability to redesign and use other tubes then the price for a 12ax7 would go down but right now demand exceeds supply and makes them cost far more than they are worth. And all of this would apply to the 6922 and 7308 to IMHO. You can still get 6dj8's at reasonable prices sometimes and 12at7's continue to be affordable for now. But there are better cheaper tubes out there and building your own allows you to take advantage of that. So who cares what some high priced name brand gear used. It doesn't matter and has nothing to do with sound quality.Once upon a time a 6sn7 might have been used. It was a good choice and made in large numbers. The same tube was also made in a 12 volt and 8 volt heater. But those tubes weren't used as much nor made in as large of numbers. So in effect it cost more back then to use an oddball tube. However the opposite is true today. It's even more dramatic when you allow youself to consider loctal tubes and the like. Again that would have ended up costing more back then but can be a lot cheaper now.
So it is not just that a certain tube sucks. It is that we, as builders, have choices that allow us to get a better sounding tube at a far cheaper price.....which just might add up to saying a 12ax7 sucks....because for the price it kinda does....and I think all of us should be able to agree on that regardless of the large number of sucessful equipment built around them.
Russ,1) You're talking about cost. TK wasn't talking about cost. He specifically said "sonically".
2) claiming that anyone should avoid 12AX7's because of cost seems silly to me, since there are many used ones available for under $15 each, AND they are also being produced by good makers like JJ, Ei, and EH for prices from $8 to $15 each.
.
Hi...the posts we've read so far in this 12AX7 issue do not hint that
there are other better alternatives than NOS or whatever makes of 12AX7s which "sound just as good if not better for a fraction of the cost" & how such better performance can be achieved for the sake of the readers here.All we want to read here is some reasonable substantiation of one's crticism on a tube or whatever interesting. Blind attack W/O backup surely revoke challenges.
In the past, I've named numerous brandnames. It is to prove to DIYers there are ways & means to build a better sounding amps using 12AX7s or whatever tubes chosen. Why not find those schmeatics & learn from those successful designers instead of bitching about whatever tube sucks publicly W/O first doing the homework properly.
I believe any makes of tubes can sound decent, brandname or no-name,
given proper circuit design. In fact, many brandnames DO use no-name
tube to save production cost.So, why not be constructive instead of setting up flames!
Enough said.
Good listening
cheap-Jack
June
exactly!
> which just might add up to saying a 12ax7 sucks....because for the price it kinda doesAnd as if that's not bad enough, the plate curves show significant non-linearity compared to a 6SL7. I don't know why this argument persists, year after year. It's all right there in black and white. Subjective, indeed.
> > And as if that's not bad enough, the plate curves show significant non-linearity compared to a 6SL7. I don't know why this argument persists, year after year. It's all right there in black and white.> >Yes, it is in black and white. Let's take our data from the Sylvania Technical Manual (12th Ed.)
Using the same B+ and lowest distortion operating point given, the output vs. distortion for each type is:6SL7
10.2V at 0.7%12AX7
7.1V at 0.2%Since distortion is proportional to signal voltage, we can reduce the 6SL7's output voltage to 7.1 and its distortion by the same ratio - in order to do a direct comparison.
7.1/10.2=0.696
0.696*0.7=0.487So at 7.1V output, the 6SL7 will have roughly 0.48% distortion compared to 0.2% for the 12AX7. Clearly the 12AX7 is more linear, given the same B+, and held within certain input limits.
This is also from the Sylvania Technical Manual, and it's the bigger picture. Although the 12AX7 does indeed have a few sweet spots, you have to search for them. It's clearly inferior to its octal predecessor under most conditions.
> > Although the 12AX7 does indeed have a few sweet spots, you have to search for them. It's clearly inferior to its octal predecessor under most conditions.> >Hi TK,
I'm not quite sure how you are looking at this chart, and then deriving the idea that the 12AX7 inferior "under most conditions".
If you average the output voltage and distortion of the 250V operating point for each tube, with the same signal voltage of 0.1V you get:
12AX7 6.34V 0.3%
6SL7 4.8V 0.5%In order to do a one-to-one comparison we lower the 12AX7's output and distortion by the ratio of the difference between its Eo and the 6SL7.
4.8/6.34=0.757
0.757*0.3=0.23%So, at an output of 4.8V, the 12AX7 will have an average of 0.23% distortion. Quite clearly this is lower than the 6SL7's 0.5% average. By half in fact.
If you raise the input voltage of each tube until just under grid current flows, as the chart shows, then the 6SL7 overtakes the 12AX7 in performance. It can do a larger output swing, clearly. So, as both Cheap-Jack and I said, it's all about the circuit, choosing the right operating point, and choosing the right tube for the job at hand.
Now, I know you think that Sylvania cherry-picked some operating points you're calling "sweet spots" - but maybe you could explain to me what a "sweet spot" is, other than simply operating the tube within its linear region. Clearly the tube doesn't have some magical region that can only be found by experimentation?
> I'm not quite sure how you are looking at this chart, and then deriving the idea that the 12AX7 inferior "under most conditions".You say that, but then focus on only one set of conditions in order to refute what I said. The chart shows numerous situations in which the 6SL7 outperforms the 12AX7.
> If you raise the input voltage of each tube until just under grid current flows, as the chart shows, then the 6SL7 overtakes the 12AX7 in performance. It can do a larger output swing, clearly.
And that agrees with what I hear. 5V output isn't real world, at least not in the gain stages I build. The 6SL7 has more dynamic range, and it remains linear long after the 12AX7 has given up. The result is not only improved numbers (which I use only as preliminary qualifiers anyway), but in the sonic impact of the stage. Believe me, I'm not biased toward these octals for any reason other than their sound. I've been comparing the sound of optimized 12AX7 vs. 6SL7 designs for years. There are indeed some 12AX7s that do a more than credible job, but they are extremely rare and likely don't match the published curves (which represent averages only). OTOH, I've never met a 'SL7 I didn't like, with the exception of the E. Eur. variety.
Hi.Let me just random take a 'real world' situation: ACE 8W SE monoblock power amp.
As per its schematic, it got a 12AX7 (Va=120V) parallel driver stage pushing a EL-34 U-L SE power stage (Va=275V, Vg2~275V U-L tapped, Vg3=0V, Vg1=16V self-bias).
Per Phillips tube date of EL-34, to deliver 8W O/P, Vi needs 9.3V (Vg1=14.5V). So with ACE EL-34's Vg1=16V, it allows 12AX7 to deliver
larger swing than 9.3V before EL-34 start g1 conducting.I'd assume the ACE designer know how to get the best out of 12AX7
& why it was chosen instead 6SL7, sonically/technically.Here are only 2 of many appraisals from the end-uers of this amp using 12AX7:-
"The best 3-D illusion of any amp. Forget technical talk, let's just listen to the music".
"These little amps are the best value I have seen in 10 years. You would have to spend 5 - 8,000 dollars to get anything even close."
Good listening
TK,Let's recap:
You made a sweeping generalization. I refuted it with specific data. You then claim that the data doesn't count, and that what you were referring to all along was "real world" situations - which, apparently to you only means max output swing.So, this probably isn't going to go anywhere productive, but hopefully this illustrated just how important the specifics are when making claims about sound quality and "linearity".
.
TK,If you're going to claim "sonic inferiority" for a tube, you at least have an obligation to mention the circumstances under which you experienced it, and the circuit in question. That's the only way it can be considered useful information for the masses.
Not doing that invites people with contradictory experience to challenge you.
.
Ok sounds good. What I don't understand is since the 6SJ7 is a pentode and the 6SL7 is a dual triode, what do I do with grids 2 and 3 of the 6SJ7?
And maybe your right about the 6SJ7, I should just get a couple and live with it.
Another question; Is the 6SL7 being maunfactured currently and are the sonics as good as the 6SJ7?
Thank you,
Steve
At this point in time, I prefer the 6SL7, but my experience with the 6SJ7 is much more limited. I do think they're both excellent, and I suspect you'll find other areas of the amplifier are more productive for tweaking. I'll add that I wouldn't change a 6SJ7 stage to 6SL7 except on a temporary basis for auditioning. It's even possible you'll lose too much gain for this to be a worthwhile modification.
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