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In Reply to: RE: if 7B4 is the best driver tube for SE DC 2A3 ... posted by deathtube 667 on March 01, 2017 at 06:59:47
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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