|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
57.66.65.3
In Reply to: RE: Linearity posted by drlowmu on September 09, 2014 at 12:49:00
He's right ! Looking at the curves , it's not a particularly linear valve . If you want an Ra 1.5k , mu 8 triode that is linear AND sounds good , then use a triode connected 4P1L . I've used 6AH4 as drivers and found them to be ok-sounding but I wouldn't use this type as an output valve .
Al
Follow Ups:
Thanks for contributing.
Thats OK Al. I have heard this tube as Finals in a two stage DC amp, and I liked what I was hearing enough to want to build it as a SET.
Are we all so SURE that a curve characteristic chart is the only factor that makes a tube enjoyable to listen to?? I think not. How about a tube's size, shape, spacing of elements, and materials?
My point is, there is a LOT to what makes up the sound of a tube ( including its implementation ! ) and I don't think we have, in this modern day and age, a good handle on what includes or excludes a particular tube as a candidate.
A number of highly respectable audiophiles do ENJOY the sound of this particlar tube type. Jim Dowdy, Thomas Meyer, Danlauadio, the late Arthur Loesch, etc. come immediately to my mind.
The real question at the end of the day is not the characteristic graph, but rather, does the amp sound really good and is it fun to listen to on music !!! Was it a musical experience ??
Jeff Medwin
I know the curves aren't everything but I have tried both 4P1L and 6AH4 hence the recommendation...
Al
OK, I do appreciate your comments, however, you are really discussing the tube in reference to your use - as in an intermediary stage, or as a line level tube. You specifically stated would not use it as a finals tube in a power amplifier, which is how I intend to use it.
Two stage DC amp.
Jeff Medwin
I give up , it's pointless trying to get through to you
I'm done...
Al
Like Al I used both 4P1L and 6AH4 as outputs. I came to exactly the same conclusions. The 6AH4 is OK sounding - smooth typical triode sound. It's indirectly heated and I wouldn't be expecting any special magic. The 4P1L, on the other hand, is right up there with 2a3, 300b, 10Y and those guys. Plenty of magic.
The 6AH4 has been around for ages, and nobody is going to "discover" it in any way. A lot of us have tried it as an output and moved on. You could say the same for 6S4A for instance. I used those in a Leak Stereo 20 in PPP. Sounded good, and a lot better than EL84s, but 4P1Ls would sound better.
There are a stack of plausible triodes you can use as outputs. 6CK4, 12B4, 1626 for instance. Tried them all at some point. And stuff I haven't looked at like 7233 and 6877. And then the Russian tubes - a few of those like 6S41, 6S19 etc etc. Goes on and on. I stick with directly heated tubes because they just sound a lot more alive. Why use anything else when you have the option of tubes like 4P1L.
I was never able to downlaod 4P1L spcs , due to a software glitch on my old computer. I looked on line at the 4P1L data today, a fresh look, and I agree with you guys, it will be a fine tube for me to use on ALTEC A7s. Very linear, and I know all about that.Actually, the 6AH4GT amp is ALSO being built as a "first amp" ever built, by a Montreal musician friend who runs tweeked ALTEC A7s-500s. I will now offer him a choice, as to what finals to use. Realize, the indirectly heated 6AH4 GT will be easier to implement for a first-time builder. Also, the fellow has a Jolida P-P KT-88 amp so the DC two stage 6AH4 amp should be a nice intital project. What finals tube will be his call now !!!
Since the Montreal musician, and I, have speaker sensitivity up the whazoo, I can easily use just one final tube, and avoid any choir effect, or skewing.
I would also AC heat the tube, as I use a special design filament transformer for directly heated tubes, having equal resistance, capacitance, and inductance across each half of the center tapped secondary.
Of course, I will use no interstages, and simply direct couple the two stage amp.
As for Rk capacitors, and am confident I know how to implement that, Andy, it doesn't phase me. Its costly, but I know what to do.
I will study the Russian tube some more, and evaluate my use of it over this next week.
Thanks for all your inputs. Sorry to have frustrated you.
Jeff Medwin
Edits: 09/12/14
The 4P1L certainly looks like a winner from the standpoint of linearity. However, there are considerable references on the 'net regarding its propensity for microphonics. There's even talk about the need to suspend it from a cable, rather then mounting it on a chassis. I don't know the extent to which this issue might surface when it's used as a power amplifier, but I think it's worth checking into before building an amp. There may be colorations that aren't apparent just from the specs (like you always say, right)? :)Jeff, have you decided against all the usual IDHT pentodes? 6BQ5 curves look pretty good in triode mode. Unfortunately, it's not enough power for my speakers in SE. I know it's not so much of a challenge to use something like this, but there's a ton of info available, lots of opinions from people who have built it, and many variations of the tube available that your friend can plug-n-play to tinker with the sonics. Just something to think about.
6BQ5 Triode
--------------------------
Buy Chinese. Bury freedom.
Edits: 09/13/14 09/13/14
The 6AQ5 will sonically beat any 6BQ5 .
I HAVE a triode connected 6AQ5 amp at home T-K.
The 6AH4 has NO PENTODE elements in it, and it sounds good to "my " ear, and to others.
Regards,
Jeff
The 4P1L is microphonic. This matters in small signal positions, but you can pretty much forget it if you have 2v in IF, and this is a definite if:
- you starve the filament a little. I run parallel filaments at 1.9v or 2v.
- you have a heavy and robust chassis. I'm talking 4mm aluminium top plate.
What you want to avoid is a flimsy steel chassis. I have 2v in from my DAC and I'm good with a 2 stage amp - 4P1L into PSE 4P1L. No suspended sockets or rubber decoupling, but a solid chassis.
I realise Jeff has his own way of doing things. Otherwise I would strongly suggest filament bias. Small cathode resistor like 10-20 ohms. No cathode bypass caps. Rod Coleman filament boards, really good filament supply e.g. choke input. One of these to each tube. A lot of care goes into the filaments - and better to use an outboard power supply. Interstage coupling with a really good interstage. Very simple circuit, but quite a big build with all the filament supplies.
I've never heard of AC filaments for the 4P1L. Even if you want to direct couple, be sensible and get some Rod Coleman boards. We've been working on this for years with the 26 as the initial tube and there are monster threads on DIY Audio on both tubes. The knowledge is well advanced and many are building with them and loving it.
Hello Andy,
Thanks for your continued interest. Over the next week I will explore on line what others do.
The German's didn't have Rod Coleman boards when they developed the tube, likely they used AC heating. Eh ?? Keep it OPEN, AC sounds very good, and is KISS !! 2 VAC is a snap, other than a custom Ef XFR, which is easy.
I will use your idea of 1.9 to 2 Volts, thanks, I usually use 5% less. Let me explore on line. Give Al my apologies please for frustrating him.
You are 100% correct, I have my ideas on implementation, but I will preview what others say and do before committing on a course. Most likely, no one has yet built a " Loftin White " 4P1L amp, but it should be OK on ALTEC A7s well wired .
My chassis is a combination of 12 gauge and 14 gauge welded steel, so it may possibly be rigid enough.
Andy, is there any advantage of a 4P1L over a Type 45, which is not microphonic and is a real triode and excellent sounding ??? Cost not a factor.
Jeff Medwin
Andy, is there any advantage of a 4P1L over a Type 45, which is not microphonic and is a real triode and excellent sounding ??? Cost not a factor.> >
You're not going to want to hear this, but the advantage is that you can use the 4P1L easily in filament bias. Not really practicable with the 45.
No need to apologise , just listen to some friendly advice for a change :)
I'd suggest building that amp as 6AH4 then maybe try 4P1L in future , octal/loctal sockets usually have similar dimensions and the biasing is very similar . It should just drop in with a different fil supply , I doubt AC will be quiet enough . 4P1L has a wimpy filament and as a result , can be microphonic but damping the chassis and running the fils under rated voltage helps . You'll get about 1.8 watts with a very nice first watt with a 4-5k OPTX . 12AY7 is a nice driver for 4P1L
Al
Al,
Ok, Ok, I will listen. I liked your advice.
I will do as you suggest, do the 6AH4 first, then consider the 4P1L, so I will leave room in the chassis for two custom Ef Xfrs, which the 6AH4 does not need.
I've ordered parts for the 4P1L possibility, loctal sockets, resistors, and am "thinking" about a custom Ef XFR design, slightly starved as you suggest.
I can ( almost as easily ) convert to a Type 45 as a final tube.
In ALL cases, I am talking two stage and direct coupled. BTW, I've used ( and liked ) 12AY7s in the last few years.
The question becomes, will the Type 45 top the 4P1L when optimized? I think it may. Can a real triode beat a pentode triode-connected, both being DHTs?? Ha !! The Type 45 would win out in my mind, not having all those extra elements, and microphony .
For the musician audio friend in Quebec, I am sure the 6AH4 will be a NICE easy first amp build, DC two-stage for his tricked out A-7s. Thanks to you and Andy.
Andy's build is very good, and specific to the sensitivity of his speakers.
Jeff
Here's the schematic if you change your mind about filament bias.If you do implement filament bias you can use an outboard supply. What you will need onboard is a good size heatsink for the Rod Coleman current regs and also the cathode resistors which have to be over-specced since they get pretty hot. I actually use Thurlby Thandar 30v 2A bench supplies to feed the Rod Coleman regs. I have a bunch of them - very handy for filament bias. But you can build a supply and choke input is nice. The signal plus the filament supply go through the same cathode resistor so filament supply must be uber clean. Cathode resistor should also be really good, like vitreous enamel. No alu clad or ceramics. You need to stay pretty close to the schematic - it all matters.
Bear in mind when you compare to the 45 that the 4P1L has a gain of around 10. This means you can use a DHT for the driver stage with sensitive speakers and 2v in. Big difference to the sound to go all-DHT.
Edits: 09/16/14
Dear Andy,Nice of you to share. What does the B+ supply schematic, with DCRs, look like ??
I think you are screwing up, more and more with this design.
Your FIRST and foremost problem is you ten inch speaker is NOT sensitive enough. This is the root of all your tube amplifier problems IMHO.
If you had 100 dB sensitive speakers, you could design VERY good tube amps and make easier aural determinations easier.
I previously critiqued your amp as having too high a dissipation across the Finals tubes. You have "hot-rodded" and upped it even more, in the wrong direction.
You are at 250.5 VDC plate to cathode, at a new and higher current, 36 mA. That is 9.01 Watts plate dissipation, on a 7.5 Watt rated plate. Why Why ?
You will answer to me " Jeff it sounds better " and I will answer " No doubt ". Tubes SOUND the best when they are run at about a Golden Ratio plate dissipation ( 62% of 7.5 Watts ) and by this, I mean they are less THERMALLY stressed and less "stressed sounding". There is an ease to the presentation when the tube is operated conservatively, and it sounds better.
BUT, (1) if your SET has less than optimal wiring implementations and (2) less than optimal power supply implementations, you will find "hot rodding" the tube dissipation " makes up " for the less than optimal execution is other areas.
Here is the rub, the hotrodded dissipation sounds better on a A-B to your ear, initially, BUT, the better performance is NEVER maintained over time. You have turned your design into a tube degradation device, and after 200 hours the higher dissipation advantages are lost, and after 2,000 hours the tubes are "toast" - need to be tossed. That is not good tube design.
Besides, IF ( a big word ) we do it right, the lack of thermal stress of a low dissipations will give predictable and better sonics over a 10,000 to 50,000 hour tube lifespan. That, Andy, is good design.
Recall how a listener to your system complained about the sound of violins, that is one place where a stressed thermally tube will sound bad. Your latest incarnation has upped the current even more.
I am not trying to criticise you, just giving you my thoughts from a few years of audio experience. 92 dB speakers are leading you astray in many subtle ways. Visit Smart845 in London. Respectfully and as a friend,
Jeff Medwin
Edits: 09/16/14
...Nice of you to share. What does the B+ supply schematic, with DCRs, look like ??> >
I leave that to whoever builds it. I'm not political about power supplies.
...Your FIRST and foremost problem is you ten inch speaker is NOT sensitive enough. This is the root of all your tube amplifier problems IMHO.If you had 100 dB sensitive speakers, you could design VERY good tube amps and make easier aural determinations easier.> >
It's a Mark Audio Alpair 10 which is more like 5". But it sounds good and covers the full range. If I got into lighter paper cones I might run into more breakup problems. I don't need a more sensitive speaker since the amp is plenty loud for my room fed with a 2v DAC. However, if I found a full range unit that sounded better than the Alpair, then sure I'd be interested in theory. Who wouldn't. There are some boutique speakers about at silly money but I don't feel any burning desire to upgrade. In an ideal world I'd have ribbons going down as low as possible, like B&G with a bass speaker crossing over as low as possible. I used to have Apogee Caliper Sigs which were streets ahead of anything else but they were too big for my room, especially when you brought them out from the walls. I have an apartment in central London and they don't come cheap, so space is expensive and at a premium. I have to have small footprint speakers close to walls, no way around that.
... I previously critiqued your amp as having too high a dissipation across the Finals tubes. You have "hot-rodded" and upped it even more, in the wrong direction. You are at 250.5 VDC plate to cathode, at a new and higher current, 36 mA. That is 9.01 Watts plate dissipation, on a 7.5 Watt rated plate. Why Why ?> >
Because it isn't a 7.5 watt rated tube. Add the screen and it's 9 watt. A few of us have done tests on the 4P1L (see Bartola Valves for example) and you will need to know that it sounds best around 25-30mA or even more. It's been used at 40mA. It likes current. And anyway I don't believe in the infallibility of the golden rule. But sure - try it at different wattages and see what sounds good to you.
...after 200 hours the higher dissipation advantages are lost, and after 2,000 hours the tubes are "toast" - need to be tossed. That is not good tube design> >
No - this isn't true at all. I leave my amp on 24/7. I replace the output tubes maybe every 6 months. They sound exactly the same after 200 hours and pretty much the same after 6 months. That's 30,000 hours. They're tough little things. And I have nearly 200 of them so what do I care! You're using expensive output tubes - I'm not.
... Recall how a listener to your system complained about the sound of violins, that is one place where a stressed thermally tube will sound bad. Your latest incarnation has upped the current even more.> >
That was something else which I fixed in subsequent iterations. But there's a germ of truth in this - using two of the same tubes in following stages can exaggerate harmonics. I don't find it a problem, furthermore many people are now starting to use 4P1L preamps and are loving the treble. It's better than the 26 for instance.
... I am not trying to criticise you, just giving you my thoughts from a few years of audio experience.> >
But bear in mind I've been building 4P1L amps and preamps for 3 years and gone through several iterations of them. So I'm 3 years ahead of you on this one. I think you'll like the tube, but you'd seriously love it in filament bias. It's the way to go.
Andy,
I want to thank you, for taking my comments in such a gentlemanly manner, as my intent was pure, and you indeed sensed that !!!
We can agree to disagree and maintain admiration of each other, if not plain old respect !! NICE !!
So what about a friendly visit to smart845, Barry in London?? I have no idea, other than his comments, as to what it sounds like. You can tell me !!
Jeff
What's smart 845? It's a Unison Research amplifier but apart from that?
Hi Andy,
I'm smart845, yes named after my first tube amp and beautiful she was too.
I met you a few years back and bought some 10ys off you to build a 10y-it-45 but it didn't work out.
I've built an amp following Jeff's mentoring and you must come and hear it on my Avamtgarde Duos.
I'm not too far away in Stoke Newington. Pop round for tea and biscuits.
You may be impressed.
Cheers
.
Have Fun and Enjoy the Music
"Still Working the Problem"
Ah! I get it.
Not my kind of speakers I'm afraid. I'm panels not horns, and even then I could only manage a thin ribbon panel for the mid/treble. So it's a full range unit by default, like 5" or 6".
Avantgarde Duo Omega isn't my kind of thing, and too big for my room really. I can do thin and tall but not wide in any way - would obscure the light from my french windows.
I'm sure it's interesting to hear, though.
I'd be interested to hear his 45 amp.He has described it in detail but I don't remember him posting a schematic.
The power supply, as described, will be very un-stable.
The driver stage is the antithesis of what I would do but with speakers as sensitive as his, *Who* knows?
You really should look him up and go have a listen.
Please let me know what you hear.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 09/18/14
Hi Tre,
I'd like Andy to pop round for a listen and get his impression. I only know one chap that is into amp building and he likes the sound but he builds those Ncore amps not tube amps.
I really would like someone else's opinion on how it sounds.
Maybe it's too far removed from panel speaker sound. I don't know.
Andy, if you want to hear some Royal Blood or Shostakovich then it's open house. Let's have a blast.
Smart845
Smart845 -
I'm in Kensington. I don't get over to East London much - where are you? You can email me.
IMHO is the 6A5G. Always dead quiet, same power and linearity as a 2A3, no heater to cathode issues which is limited to 200v max on the 6AH4.
You can run one and it's driver (assuming 6.3v) off the same filament winding. So you need only 2 6.3V/2A windings for a stereo amp. One more if you run a tube rectifier. If direct coupled the driver must then meet heater/cathode ratings, or add a separate filament trans for the drivers.
If IT or RC coupled then just 2 is fine.
The only IDHT I know that can cope with a good DHT is the French R120 from Radiotechnique or Dario. It was mentioned as a good sounding tube by Jean Hiraga, the man who brought the attention of small DHT's and horns back to Europe and the US when most of the best stuff had gone to Japan or to the dump.
The very first SE amp I made was with R120, and I can confirm they are really good sounding.
I love those tiny cathode sleeves on the 6a5g with the insulated heater wire inside.
Call me when you get a chance and I'll tell you about the guy in southern Oregon.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
"You specifically stated would not use it as a finals tube"
Its linearity becomes worse in that application due to increased voltage swing.
--------------------------
Buy Chinese. Bury freedom.
One-note samba.
I am not so concerned with just ONE theoretical aspect of a tube amp's design ... which you would want to focus upon.
This is an amp that will operate 99% of the time at 100 to 500 milliwatts of output power on 100 dB plus sensitive speakers.
You certainly are not trying to be helpful, you are just trying to criticise me personally, which you have done repeatedly over the years whenever you think you could get away with it.
Best wishes,
Jeff Medwin
"you are just trying to criticise me personally"You couldn't be more wrong. I would have asked the exact same question of any inmate who suddenly announced they were going to build a SET with the 6AH4. If you like the sound of this tube, fine, but that's no reason to lash out at people who ask a simple question about how it will be applied.
--------------------------
Buy Chinese. Bury freedom.
Edits: 09/11/14
OK T-K,Well then, I apologize to you. You have posted negatively about audio things I do in the past, over many years now, and it caused me to over-react.
Yes, I do like the way this tube sounds. Yes, I do not get too upset at all about its curves, the transfer characteristics doesn't "tell all" to my way of thinking. Yes, I want to build a SE DC amp with this in the finals position.
I am motovated by two things T-K.
First, and foremost, in 2013 I listened to a two stage DC Push Pull amp ( designed and hand-built by the late Arthur Loesch - used the same tube types I intend to use ), and I LOVED the way it sounded to me. Mesmerizing.
Second, some of the builders on-line ( experienced, respectable individuals ) have used this tube, typically in a line level preamp, and they too much like what they heard. Names were referred to in another post in this thread.
Thats all, there are no guarantees when you do a new design, but the proof of the pudding...blah, blah, blah, ....is NOT just the load line !!!
This will, to the best of my knowledge, be the first single ended triode two-stage direct-coupled amp with 6AH4s as the final tube, and additionally, it employs what I call a "modern power supply". These factors alone make me wanna get off my butt and build it, just to hear it !! Its fun. Give me a couple of months and I will know more !!
I'll post photos as I go along as some like to see them.
Jeff Medwin
Edits: 09/11/14 09/11/14
Jeff, I'm always interested in seeing how other people build their gear. And the fact is, some have used tubes with curves that look worse than the 6AH4, and they seemed to like the results. One that comes to mind is the 1626. I wondered for years how a tube with such awful curves could produce a decent amp. The answer is that it doesn't, unless one is willing to overlook the flaws indicated by the curves, which do indeed reach the output of the amplifier. I arrived at that conclusion after one of the users finally made a measurement and posted the results:
Realizing how poor this performance is, the builder even remarked that it's nothing to worry about. Most of it is 2nd harmonic, which "can be accepted by human ears."
My point is, Jeff, that if this is the sort of amplifier you're building, that's fine by me. Personally though, I can't stand listening to designs that produce so much distortion, even when its 2nd harmonic. So, when I see something that seems amiss (like the 6AH4 curves), something that will likely produce an amplifier I wouldn't want to listen to myself, I ask questions. Simple as that.
Keep up posted on the progress!
--------------------------
Buy Chinese. Bury freedom.
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: