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In Reply to: RE: Vintage Tubes posted by tube wrangler on February 28, 2017 at 10:21:25
Then why is your friend , JM/drlowmu, using something different?
A low Rp driver tube of some kind?
It would seem like using the 7B4 would be the way to go since the "tube wrangler" himself uses it.
I consider both Tube Wrangler and Dr Low Mu friends - but I don't use the 7B4/12AX7/12BZ7 in my 2A3 amps.
First, the 12BZ7 was recommended-- by me! The pros and cons and the need
to drive into less efficient (and less costly) wiring, etc., for Jeff's new lower-cost build meant that a bit of extra driver power was needed for this less expensive build-- not for what I do in my more expensive build where everything must be as perfect as possible..
The 12BZ7 is controversial in that it's not perfectly linear on paper. It's good for Jeff's application because it has a high amp-factor and will in addition provide some extra current needed to drive less efficient wiring in the build. The linearity problem is NOT really a problem. The 12BZ7 can be run where it will easily be linear enough for its intended application.
With that said, Jeff is the final decider for his amps-- not me!
There you go-- more than one way to skin a different Cat.
I would not have guessed 12BZ7, but it seems logical based on your transfer efficiency concepts to use that tube in a budget build.
Each triode section of 12BZ7 is similar to a parallel 12AX7 from what I have read about it.
Thanks for the information.
You got it!
Incidentally, there are reports of early failures
regarding the use of 12BZ7 tubes.
Plug-and-try, it seems, is not doing the job.
People have simply plugged these into circuits
designed for 12AX7, etc., and see if they
hear something-- different. Trouble is, what are
the new operating points now? DID THEY CHECK THAT
against 12BZ7 Design-Center values? AND, try to
operate UNDER THOSE?
Just plunking a different tube into another tube's
circuit isn't useful tube life data!
The tube is no different in build quality than similar
types made by the same tube factories. Why would one
age faster than another?
It's operating points and nothing else.
I say, no need for you to answer any questions to anyone, on what I am going to build.
The proof of the pudding, will be in the listening, or, the A-Bing, which I would readily invite - when my new monoblocks are completed.
You, Dennis, said it well : " The linearity problem is NOT really a problem. The 12BZ7 can be run where it will easily be linear enough for its intended application."
As you say, there are lots of ways to skin the cat.
Have a good day !!
"The 12BZ7 is controversial in that it's not perfectly linear on paper."
That might be the understatement of the year.
"...will in addition provide some extra current needed to drive less efficient wiring..."
Wire takes current to drive it?
I think you need to explain why.
"The linearity problem is NOT really a problem. The 12BZ7 can be run where it will easily be linear enough for its intended application."
Please show us where you would operate the 12bz7 to make it "linear enough" for a low distortion audio application.
Have Fun and Enjoy the Music
"Still Working the Problem"
The 12BZ7 isn't really any less "linear" than a 12AX7. The curves you posted are almost exactly those of a 12AX7 but with "Ip" multiplied by 2. There's a reason for that. For all practical purposes, each section of a 12BZ7 is almost exactly a 12AX7 with both sections paralleled. 12BZ7 gm is double that of 12AX7, rp=1/2, If=2x, u=100, etc. If the 12BZ7 has a weakness compared to the 12AX7 it's excessive microphonics. Every one I've tried to use was a microphone. YMMV
I disagree with you, I do not think the graphs are similar.
But the graphs, and " maximum swing analysis " are NOT the sole reason to use, or discard, any tube. There are other factors one must weigh. The less-linear graphs I see, won't stop me in my intended use of the tube, one time in my audio chain.
In what gear were you employing the tube, preamp or amp, may I ask you ??
How many stages, one, or more in series??
Aside from microphonics, how did it compare to a 12AX7 sonically-speaking, in your circuit, and from your direct experience ??
Thanks in advance.
There are minor differences in the curves, mostly at extremes. In part no doubt an artifact of manually fitting a smooth curves to discrete data points as was done in those days.
My experience with 12BZ7 was in an attempt at improving drive capabilities of two traditional PP driver topologies that utilized 12AX7: Mullard circuit and gain stage direct coupled to split load inverter. In both situations the sound was pretty much same as 12AX7 but didn't do much serious listening before moving on because of microphonics. Maybe I had a bunch of bad examples of the type. Maybe they'll work out fine in your apps. Fortunately they're still inexpensive so no great loss if they don't work out. As always with tubes like this, YMMV.
Good observations. For preamp use, Low-Noise tubes
are chosen. Anything special about "low noise" tubes?
The plates are shorter! The less area, the lower the microphonics.
(and incidentally, the lesser the musical dynamics-- if all else is equal).
I'll be leaving operating points to the user of any tube-- it's
his amp, not mine....
I love tubes that have a large surface area and low operating currents, and low thermal stress levels.
Lots of dynamics VS distortion levels. Of course, all tubes are
microphones in one way or the other. As always-- there are degrees of trade-off.
Thanks for pointing out your observations to all of us!
Hey, I feel your questioning, on a public forum, is rather rude to Mr. Fraker, and way way off-base. It seems to "me" like it was posed, not as a way to learn something about audio design, ( because believe me, Mr. Fraker has many good reasons to choose what ever tubes he likes - and YOU would learn positive things from understanding his reasoning ).
No, unless I am mis-reading you totally, it SEEMS to me, you just try to put someone on the defensive. How rude, how mean spirited can you be??
Realize, I am a different person than Mr. Fraker, and I have free will, to do and build what ever I please.
If this was done in the spirit I envision, I would pose the following -- let me put YOU on the defensive :
You don't even know what the tube would be, do you ?? NO!
Do you know who suggested it to me, to try out ??? NO!
Does the amp exist, and in working order in my home....NO !!
Am I presently "actively" constructing it?? NO !
Am I planning to build something ?? YES !! Of course.
Have I ever used a 7B4 in any of my amps?? NO!
Did Mr. Fraker's recent AA postings, of a 2 mA , mu of 100 driver, sink into your mind ?? PROBABLY NO !!
Can ( and do ) YOU ( and I ) know how to build a better performing SET amp than Mr. Fraker? NO !!
Can any one else in SET land?? ..... I DOUBT that, very much.
Have I grossly mis-read your intent ?? ' Don't know !! Perhaps. YOU can certainly explain, and tell us. If I am interpreting you wrong, I apologize in advance of me knowing.
Well, there you have it sir.
You mentioned switching from the 1/2 of 12AX7 to a high mu/low Rp driver for DC 2A3.
Since DF knows you and what you are doing with tube amps, I asked his opinion since he is the MAN of SE DC 2A3 amplifiers around here.
I probably should have contacted you offline for that info.
No problem. I over-reacted, because I get tired of some people's posting, and likely vice-versa about me !!
None of these tube devices are perfect. We have to do and use whatever we can, the best compromise, and design with them !!!
I see you use 45s. I could not get that tube to go well in 2015 -2016. In the middle midrange, I always hear a broad but shallow suck out, despite it doing other lovely things that would catch people's attention. Very noticeable on well-recorded solo piano.
Dennis Fraker, heard the same Type 45 traits in his place in Montana. Listen to a JJ 2A3-40 in your amp, don't really have to change the 5K output trannie, just the Rk, and not even that on a first-try basis. It ATE my ST 45s.
I am selling all my 45s, sixty eight of them, on eBay. I start with 47 of the TV-7 passable tubes, tonight, 30 auctions, spaced apart every seven minutes. I have a dozen JJ 2A3-40s now at home, enough for me, two times over. Just pop in some JJs and compare them, see if you can borrow two, using 45 biasing even !!
Just curious, how many JJ2A3's do you own?
I have 6 right now and expect these to last at least 10 years since I'm biasing low.
Twelve . 10,000 LPs.
I'll typically be at 47 mA and about 260 P-K, or 12.22 Watts dissipation.
I figure I am covered 'till age 200.
I run mine at 45-46ma so I should be good!
I'll typically be at 47 mA and about 260 P-K, or 12.22 Watts dissipation
At this bias point how many hours do you think you can get out of this tube? I know it's a 40W tube and at this dissipation it is loafing, but I still wonder what that number might be especially as compared to a regular 15W 2A3 that is run under the same conditions.
I would think a 300b operating at those points would last a lifetime.
And that's what a JJ 2a3-40 is, a 300b with folded filaments.
It does have the mu of a 2a3 but the same limiting values as their 300b.
450v, 40 watt, 70ma fixed bias and 100ma cathode biased
It has the same inter electrode capacitances and that's interesting because if the mu is different then the spacing between elements should be different but still the inter electrode capacitances are list as being the same.
I really think the two, the JJ 2a3-40 and the JJ 300b, are the same tube with the filament center tapped for the JJ 2a3-40 and the center tap is connected to one filament pin and the two ends are both connected to the other filament pin.
Have Fun and Enjoy the Music
"Still Working the Problem"
I think you're probably right on nearly all counts.
Interestingly, on JJ's website, there are several hints that the
2A3-40 handily outperforms their 300B. Pretty strong hints at that!
That's what has happened with me. For a long time, I just popped
the 2A3-40 into amps that had been voiced for other 2A3s-- the
likes of old RCA's, The EML mesh and solid-plate tubes, and etc.
Even Sovteks and Electro-Harmonix (a premium Sovtek-- has
gold-flashed grids, and does sound better. Looks like the
Kevin Hayes (VAC) had once mentioned that you had to voice
for the JJ tubes... they're different.
That they are! If I voice an amp for them, other tubes won't
be at their best. If I voice for those at their best, the
JJ sounds good, but fairly ordinary.
It's interesting that when you get the JJ 2A3-40 settled into
what it really wants, it can and will give you everything you
could ever ask for about recorded music. It will sound just
like that expensive Berkeley Audio Design DAC that costs
$16,000.00 That's saying a lot because that thing is GREAT!
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