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Its so exciting when the VAC power is applied by Variac for the first time, and it all works just as I planned / designed it !
To my best understanding, this is the very first 6AH4GT single-ended direct-coupled audio amplifier ever built. Now... to break it in.
Jeff Davidson did NEAT amplifier construction, mine is a bit different. Few are willing to show under-the-hood shots of their work.
Jeff Medwin
Edits: 10/18/14Follow Ups:
Hi,
This thread is disgusting to me !! A new low. We have one or two people relishing to point-out to me that the large scale swing of a 6AH4GT is not totally linear, ( which was something of which I was totally aware. )There are many amps that use equal or worse characteristic curve tubes as Finals, and no one usually mentions too much about it.
My main point is, there is MUCH more to designing and building a good amp, or dare I say a GREAT amp, than the single / narrow focus some seek to eschew.
Also, I am building this despite large swing curves, because I KNOW I can build a compelling amp, with my skills and approach, moreso than almost everyone else's Type 45 SE amp. ( A no-brainer tube - which is considered more linear ) .
So, what I need to do is finish this, and "put it up against" some "hot" Type 45 SE amps, and watch people's faces as the A-Bing proceeds !! Ha.
There is more than one way to skin the cat!! You can "handycap" Jeff this choice of a tube, and I can still produce a GREAT amp, maybe better than most and certainly all the posters who may chose a more linear tube, and have been critical in this thread of me. Thats ironic in my opinion.
Oh well, have a good day. I am having fun. Hope you are also. Don't try to teach me things I already know about, I am trying to show by example ( this modest amp and its build ), despite what you THINK you know, what end is up !!
Such Chutzpah on my part !!
Jeff Medwin
Edits: 10/20/14
nada aqui
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Buy Chinese. Bury freedom.
Looks very nice Jeff. Excellent workmanship as always.
The top picture makes me want to start a fire, put on my fuzzy slippers, pour a little egg nog/whiskey and spin a couple of sides of Christmas tunes.
On a serious note, I finally got around to measuring the power transformers and chokes for the 2A3 monoblock build. I will forward the data in the next couple of days so we can calculate the values for the rest of the components.
James
Dr. FrankenMu's creation is alive. God help us!
So how does it sound on the Altecus Votorius mystery horns?
Have fun.
I got home from work this evening and just fired it up a second time. Been running 15 minutes. I am stoked, flabber-ghasted, all the supply and audio voltages are within 1/2 to 2% of what I simulated, computed, designed them to be !!!
All my A7-800 drivers are presently sans enclosures, so I will hook up the EV12 TRX and give that a go. Needs break in, solder joints, caps, etc etc.
Amp is pulling about 60 mills total B+ current out of the stock ( but rewired ) Dyna ST-70 power trannie, so its loafing, mildly warm to the touch !!!
Jeff
Seriously? Your solder joints have to break in? Is there no end to this BS?
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Buy Chinese. Bury freedom.
Dummy, it takes at least eight hours .
Jeff Medwin
~!
The Mind has No Firewall~ U.S. Army War College.
Nice layout. I have to say though, for the benefit of other members, personal listening impressions are secondary to basic performance. It will be helpful if you post measurements such as frequency response, distortion and output hum before telling us that you've achieved sonic nirvana.
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Buy Chinese. Bury freedom.
Edits: 10/18/14 10/18/14
6ah4
185 volts plate to cathode volts at idle.
30ma. idle current.
-15 volts grid bias.
5K load impedance.
A 30 volt peak to peak input signal yields .88 watts RMS power with a plate voltage change of -109 volts to +85 volts.
I know someone can tell me what % of harmonic distortion that is.
A 20 volt peak to peak input signal yields .42 watts RMS power with a plate voltage change of -70 volts to +60 volts.
I know someone can tell me what % of harmonic distortion that is.
A chain is only as strong as it's weakest link.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 10/20/14 10/20/14
That's still just a calculation, and it's based on a chart that may or may not be accurate. It's unfortunate this guy won't bother to actually make the measurements necessary to determine real-world performance of anything he builds.
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Buy Chinese. Bury freedom.
"That's still just a calculation, and it's based on a chart that may or may not be accurate."That's true but given that, it's still not very encouraging.
There are published plate curves (not for the 6ah4) that are actual measured curves for real tubes.
That will still not tell us exactly what the tube in our hand will do, but close.
I wish someone would publish more actual measured curves.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 10/20/14
Since you have an octal socket for the 6.3V "final", it might be interesting to swap in a 6A5G for the 6AH4GT, even with less than ideal voltage, to make a sound quality comparison. Might have to move a couple wires to different pins, and maybe adjust the Rk. It certainly "should" sound better...
Not necessarily. What is the interelectrode capcitance of a 6A5G, grid to plate, versus a 6AH4GT, which is only 4.4 pF.
Jeff
and yes, with less than 1 ma driver current, there would be less highs.
BTW a 2A3 has 16.5 pF, and you had no issues with that, right?
~!
The Mind has No Firewall~ U.S. Army War College.
This is a low power amp, for ALTEC, K-Horns, etc. I am going after SE Type 45 amps with this design. I wanna see the expressions on thier faces when the A-Bing occurs. Fun.
Jeff Medwin
I can appreciate the punk rock underdog attitude/approach/choice of "final", but linearity issues just won't go away.
For example I heard an SE amp with a paralleled 6SN7 "final" that is/was
probably about the same power as Franky there, but had to be lower THD.
Impressive on VOT's at reasonable levels. Another choice would be a 5687 "final", both are significantly more linear.
I would not worry about one parameter of a tube. Besides, you don't KNOW my load line and THD, etc, it has not yet been measured. Thomas Meyer never complains about a lack of linearity in a 6AH4GT. I think you guys are just trying to blow smoke up my ***, because I CAN build a fine amp with this...maybe, just maybe, better than anything you guys have heard !!
There are so many things that make ( and usually break ) a SE amp GSH.
This amp has some very new things in it, and I have been listening to it for two hours now, and it shows real promise, excites me. What I am hearing initially, is offering me musical clues - things we never heard and have gotten before, out of very familiar music and recordings.
I am experiencing a new level of dynamic expression and contrasting, very subtle and basic dynamic contrasting, and a free-flow, never heard on amplified playback before!! Dennis Fraker is getting this extra performance out of his current builds, and certainly his ideas and parts experimentation, is assisting me.
There is a break-in required. I KNOW I have work to do on optimizing my Rk bypassing choices, which I look forward to exploring - in coming weeks. I even have a bad connection, causing hum, which I have to track down and repair. But initially, I am pleased with the way it plays, the new performance never before gotten, and now I would just like to make the best of it.
When I am done with it, this amp should just EAT the "typical" most linear triode tube amp you can think of, because of the overall design and attention to details. Its impossible to beat a two stage DC SE amp IMHO. Everything matters however !!! We just have to learn how to build a good one !! Oh well, let the fun begin. Back to mo' listening for now.
Jeff Medwin
~!
The Mind has No Firewall~ U.S. Army War College.
Hi!
I only use the 6AH4 in a transformer coupled preamp. There the distortion is not as bad due to the rather low signal swing.
Thomas
I got good results with a CCS loaded 6AH4 driver but I would not use as an output stage . If I needed a mu=8 Ra 1.6k triode for an output stage , I would go for a triode connected 4P1L .
I think to get any decent linearity out of a 6AH4 output stage , local feedback would be required (OPTX secondary in the cathode circuit) .
Al
~!
The Mind has No Firewall~ U.S. Army War College.
Hi!
I just wanted to clarify how I use this tube.
Besides that I prefer to stay out of this discussion
Thomas
nt
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Have Fun and Enjoy the Music
"Still Working the Problem"
So Thomas, if I may be so bold as to extrapolate from what you just said, if the 6ah4 was used as an output tube the harmonic distortion created by the 6ah4 WOULD be unacceptable (or at least "bad") do to the tube's nonlinearity at those higher signal swings?
Thank you.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
The emotional investment you've made is more than obvious. OK. When you calm down, you may remember that physics are involved. IF (huge IF) you exercised the same fervor applied to a different "favorite discovery of the moment" then you might have a new "favorite discovery of the moment".
Of course, none of this is any form of discovery whatsoever, as the 6AH4GT was designed and tested thoroughly, what, 50 years ago? As well as having been "processed" by the Japanese enthusiasts, what, 20 years ago ?
Again, OK fine. My suggestions were meant to remain in parallel with your wish for alternatives to the usual, while simultaneously showing more potential for measured performance. If this is an ugly offensive proposition from your POV, then it is. Why?, we can only guess.
we should all write on the chalkboard {100 times} before we commenced building our first amplifier..."A circuit with one tube type can be changed to sound like another tube by just changing its plate voltage, bias or load impedance. When a different tube is used, it’s different also. When changing operating points, many like tubes can sound exactly the same"Jeff, should have the eraser taken away and write a thousand times.
The Mind has No Firewall~ U.S. Army War College.
Edits: 10/19/14
What are you trying to say? What is your point ??
Jeff Medwin
You do realize who you're talking to, right? Scientific conceptualization is for suckers.
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Buy Chinese. Bury freedom.
is a chore, but behind the facade, is what he believes are good intentions. I don't worry about that anymore.
It is his beliefs that don't have measurable proof, that are always the bone(s) of contention. I think we all have found evidence of unmeasurable "improvements". He may have "found" more than are easily believable. None of this is news.
His identification with Christopher Columbus however, does consistently fuel
equally exaggerated criticism. No news there either.
Worst part is when he sites physics as support for an argument, while moments later poo pooing another, who out does him with the same amo.
It's somehow worse than hypocrisy.
He doesn't play fair, yet he's not alone...
Jeff, that looks really great. It may not look super neat in a way, but the thought, planning, commitment and skill are clearly evident. Nicely done.
Cheers.
"In the beginner's mind there are many possibilities, in the expert's mind there are few." Shunryo Suzuki
I presume those green things are K75 caps (nice choice), but what are those black rings around them as mounts ??
Jon,
When you use mutiple paralleled film caps, say to bypass a Rk as I am doing in this case, it is important NOT to have the bodies of one film cap, touching another, as their combined performance, when touching each other, degrades substantially.
How to keep the film cap bodies from touching? Several ways.
My use of 1/8th inch O-Rings act as a "spacing barrier", so the green K75-10 does not touch any other film cap in the build. Another method might be to use GE Silicone between the caps to space them apart. These O Rings are actually my original idea, first time I am trying it out.
Jeff Medwin
Jeff, I believe I recognize those black film caps, where do you source them from?. Thanks. JH
"... it is important NOT to have the bodies of one film cap, touching another, as their combined performance, when touching each other, degrades substantially."
Which parameter(s) of the capacitors degrade when they touch?
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Buy Chinese. Bury freedom.
Their sonics degrade, very audible to me, others.
Jeff Medwin
I don't believe you. You hear what you want to hear. This is another urban myth concocted while sitting on the throne.
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Buy Chinese. Bury freedom.
I separated my caps using Herbies audio lab material and noticed an improvement. Possibly due to reduced vibration between the caps.
There are a lot more devices that eschew traditional wisdom but have a great effect on the listener. Check out Alan MaherDesigns for some more creative out of the box thinking that really works.
You guys gotta open up to some new ideas.
How about the 5 pin tubes from EML that have a filament centre tap?
RFI wrap around base of tubes?
Paralleling hookup wires?
The list goes on
After a brief read, I didn't see anything on the Alan Maher Designs website that isn't grounded (ha-ha) in known science.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Especially when you have ZERO experience with the subject you were asking me about !!A well designed two stage amp, direct coupled, is very transparent, and, the superior KISS design allows people with normal hearing to learn and hear things they never knew about before. You become, in a way, more discriminating.
Jeff Medwin
Edits: 10/18/14
O rings for damping resonances and vibration.
Jeff,
Nice looking work..
Give us listening impressions when ready :)
BTW. I have had a bad experience with compression fittings on grounding schemes. Looks like you filled them with solder...I mitigated the same way.
Keep us posted..
You've inspired me to get on with my build...
Stuben
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