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In Reply to: RE: How to use the 4P1L posted by drlowmu on September 13, 2014 at 08:29:16
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
Follow Ups:
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.
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