There's a thread about these.
I remarked there that it is very similar to EL822; I used these in my 813 amp as pentode sink; 6P15P with its high Ra and good gm ((up to 15) would also be excellent. But in the thread Wavebourn showed us what a nice triode it makes, mu of 20 Ra about 1.2k.
Paul
I remarked there that it is very similar to EL822; I used these in my 813 amp as pentode sink; 6P15P with its high Ra and good gm ((up to 15) would also be excellent. But in the thread Wavebourn showed us what a nice triode it makes, mu of 20 Ra about 1.2k.
Paul
Found an optimal distortion point if this valve needs to be run at maximum power. With Ia=35mA, Vg=-15.2V, Va=241V, you can get THD to 0.13% (Vo=+22.22dBu). Yes, it will be at the edge of its anode+screen power dissipation:
http://www.bartola.co.uk/valves/wp-content/uploads/2012/06/12P17L-3.jpg
Keen to see where people have actually biased this valve and are happy to test this point?
http://www.bartola.co.uk/valves/wp-content/uploads/2012/06/12P17L-3.jpg
Keen to see where people have actually biased this valve and are happy to test this point?
Back to the 4P1L and SE amplifiers. I've been trying without too much success to build a 300b SET which sounds as good as my 2a3 PP amp, which has differential 26 input stage and 4P1L driver stage.
The problem I keep getting in SE is that I hate and loathe cathode bypass caps except in the output stage where I put up with it. My driver stage has been using a 46 tube into a Hammond 126C interstage. If I use no cathode bypass on this stage the sound is vivid and exciting but ragged. Stick a bypass on it and the sound goes dead as if a fog has descended on the music. It all just gets smooth and boring. I can't live with either. I did try battery grid bias which was OK-ish, but gave all that up when I found how good a differential PP amp could be with all DHTs. The diff pairs sit on CCSs and pentode sinks so no issues with cathode bypasses.
So into this situation comes the 4P1L as a driver. I just tested this stage with the Hammond 126C interstage as a preamp, and was pretty astonished by how good it was. The idea is to use filament bias, and this is working very nicely. I have 18v going into the 4P1L, which gives me a bias on top of the 25 ohm cathode resistor (25W) of just over 16v. I'm running the 4P1L in parallel filaments with slightly starved filament, so about 1.8v and just under 600ma. I have 165v on the anode, and that's about 13mA. The 126C is rated for 15mA and sounds at ease with this operating point.
Sound is fast, clean and transparent - very clear dynamics and low level detail. Mogliaa has already told us all this, so I'm a bit slow on the uptake. In fact I've known about this tube for ten years or so - never bought any until this year. I was scared of the microphonics but they're fine as a driver, and seem to be under control in the preamp even.
So the plan is to use 4P1L into 126C and filament bias as a driver stage for a 300b. I have high hopes for this. It'll take a few days to construct but judging from how good this setup is as a preamp, I have very high hopes. I'd then use my 26 preamp as the input stage. Gain is OK with a 2v CD input and my average sensitivity Alpair 10 drivers (around 89db).
I'm really looking forward to this! It may resurrect my 300b SET and get it back off the shelf. Yippee - no cathode bypasses!
Andy
The problem I keep getting in SE is that I hate and loathe cathode bypass caps except in the output stage where I put up with it. My driver stage has been using a 46 tube into a Hammond 126C interstage. If I use no cathode bypass on this stage the sound is vivid and exciting but ragged. Stick a bypass on it and the sound goes dead as if a fog has descended on the music. It all just gets smooth and boring. I can't live with either. I did try battery grid bias which was OK-ish, but gave all that up when I found how good a differential PP amp could be with all DHTs. The diff pairs sit on CCSs and pentode sinks so no issues with cathode bypasses.
So into this situation comes the 4P1L as a driver. I just tested this stage with the Hammond 126C interstage as a preamp, and was pretty astonished by how good it was. The idea is to use filament bias, and this is working very nicely. I have 18v going into the 4P1L, which gives me a bias on top of the 25 ohm cathode resistor (25W) of just over 16v. I'm running the 4P1L in parallel filaments with slightly starved filament, so about 1.8v and just under 600ma. I have 165v on the anode, and that's about 13mA. The 126C is rated for 15mA and sounds at ease with this operating point.
Sound is fast, clean and transparent - very clear dynamics and low level detail. Mogliaa has already told us all this, so I'm a bit slow on the uptake. In fact I've known about this tube for ten years or so - never bought any until this year. I was scared of the microphonics but they're fine as a driver, and seem to be under control in the preamp even.
So the plan is to use 4P1L into 126C and filament bias as a driver stage for a 300b. I have high hopes for this. It'll take a few days to construct but judging from how good this setup is as a preamp, I have very high hopes. I'd then use my 26 preamp as the input stage. Gain is OK with a 2v CD input and my average sensitivity Alpair 10 drivers (around 89db).
I'm really looking forward to this! It may resurrect my 300b SET and get it back off the shelf. Yippee - no cathode bypasses!
Andy
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Andy,
Sounds a very promising setup. Keen to see your results!
I'd rather run the 4P1L at above 20mA of anode current. That is where it performs the best. Have a look at my tests on the 4P1L linearity and sweet spot :
4?1?/4P1L THD sweet spot | Bartola Valves
Here is the pre-amp version I built which sounded brilliant. I'm sure that a differential pair is worth going for after your results with your PP amplifier!
4?1?/4P1L triode curves | Bartola Valves
cheers,
Ale
Sounds a very promising setup. Keen to see your results!
I'd rather run the 4P1L at above 20mA of anode current. That is where it performs the best. Have a look at my tests on the 4P1L linearity and sweet spot :
4?1?/4P1L THD sweet spot | Bartola Valves
Here is the pre-amp version I built which sounded brilliant. I'm sure that a differential pair is worth going for after your results with your PP amplifier!
4?1?/4P1L triode curves | Bartola Valves
cheers,
Ale
I'd also rather run the 4P1L with more current, but I can't into the Hammond 126C, which is rated 15mA. I have a few of these interstages, so my hands are tied there. It's a good sounding interstage for not much money - only slightly behind the Lundahl stuff. It's bifilar wound.
This preamp has more treble than the 26 - it's very noticeable. Did you experience this? I think the bass is better too. It's not so euphonic as the 26 - brighter sound. I'm enjoying this right now. I have 4P1L preamp into 4P1L diff pair into 2a3 PP. Two stages of 4P1L. It's astonishingly clear.
Andy
This preamp has more treble than the 26 - it's very noticeable. Did you experience this? I think the bass is better too. It's not so euphonic as the 26 - brighter sound. I'm enjoying this right now. I have 4P1L preamp into 4P1L diff pair into 2a3 PP. Two stages of 4P1L. It's astonishingly clear.
Andy
Overlooked that, yes. There is a 126 gapped at 30mA, no? The 126 is an interstage not for PP circuits. How are you using it?
My 4P1L had a stronger bass for sure. My wife who has a musician ear picked it up and always preferred the 4P1L to the 26. I was kind of frustrated as the 4P1L cost was peanuts compared to the 26 with LL1660 OT. Being fair to the 26, I haven't improved its design with all the newer recommendations you made, etc.
Anatoliy said it before and I had to test hundreds of valves to confirm: haven't found any more linear one than 4P1L
Anatoliy said it before and I had to test hundreds of valves to confirm: haven't found any more linear one than 4P1L
Right. And it still is the major sleeper tube.
Yes - a real sleeper tube. Listen to it and all those uber-expensive 12AX7s and 6SN7s and those Telefunken tubes with diamonds on the bottom start to look pretty silly.
Ale - yes there's a 126B. Twice the current and half the inductance. They're both single ended, and really good quality and value. Another sleeper.
What I've noticed with this 4P1L preamp is that it is absolutely the best ever for jazz. The double bass is solid and clear and the drum kit has to be heard to be believed - snare drum, brushes, floor toms, hi-hat, ride and crash cymbols. It's really, really lifelike.
Andy
Ale - yes there's a 126B. Twice the current and half the inductance. They're both single ended, and really good quality and value. Another sleeper.
What I've noticed with this 4P1L preamp is that it is absolutely the best ever for jazz. The double bass is solid and clear and the drum kit has to be heard to be believed - snare drum, brushes, floor toms, hi-hat, ride and crash cymbols. It's really, really lifelike.
Andy
I'm glad you like it. If I look back when I started the 4P1L preamp thread, there were a lot of discouraging comments about the microphony of it, but few comments about its sound. When I built it got very impressed with its sound. I listen to Jazz most of the time (e.g. Coltrane, Monk, Davis, Rollins, etc.) and is definitely a great one. With its low anode resistance (like the 71) and current capability it's great with a gyrator load.
Will buy a pair of IT and try them out as well!
Will buy a pair of IT and try them out as well!
I did a 4P1L---4P1L SE DC coupled amp which suffered quite bad microphony , if the chassis was tapped there would be a noticeable 'poing' that lasted a few seconds , sometimes when I hit pause there would be a bit of a poingy sound too . I find as output stages microphony is fine but as linestages microphony poor although I do use 98dB speakers so just about any hum/buzz/filament clanging comes through . Running the fils under 4v seemed to help a little to tame the microphony
316A
I thought you were still using this amp, maybe in a second system? I can't remember where you are with speakers - last I heard were treble horns and big bass units, so I can believe you need to take extra precautions with your amps. My system is quite benign - Mark Audio Alpair 10s. They're like Jordan JX92s but better, smoother and more musical when used full range. My chassis all have 4mm alu top plates so quite massive, and my room is carpeted, so I get away with quite a lot as regards microphonics. I even had a 1G4G preamp for a while, and that takes some doing. That rang like a bell in other people's systems.
So, depending on the system, 4P1L preamps are not impossible with starved filament. Did you find some of the tubes were more microphonic than others? Maybe selecting them helps?
Andy
So, depending on the system, 4P1L preamps are not impossible with starved filament. Did you find some of the tubes were more microphonic than others? Maybe selecting them helps?
Andy
Hi - I have been reading this thread with great interest. What would be the Rp at this operating point?
I am thinking of trying out the 4P1L as a driver for my SE 45 amp with an interstage transformer. I have a couple I can choose from. I may try it with these:-
Valve Transformer VT1399
Martin
If you can get 2W from 4P1L driver that means can get enough of voltage swing to drive 45 tube for 2W of output power.
OK I take your point, but my question is what is the plate resistance of a single 4P1L at the chosen operating point?
Deco-doctor
Have a look at the 126B and 126C at Bluebell Audio - look at Transformers > Interstages. They are exactly the same price as Danbury and probably at least twice as good. Also they are bifilar wound and have a known and stated inductance. Philip at Bluebell is very helpful and knows his tubes.
As for the current to run through the 4P1L, I was shocked to find that in my 4P1L preamp with filament bias I was running less than 2mA through them. I still haven't got to the bottom of why the current doesn't agree with the curves. Anyway, I actually like the sound at low currents - it has thinner mids and more apparent treble but it's very clear. 7N7 who is also working on this project prefers the sound at higher currents because it's fatter in the mids. I use the 126C and I want to set up some kind of rig where I can vary the current through the 4P1L as I listen to it. I'd like my ears to have a say in this, even though the results may be counter-intuitive.
Andy
Have a look at the 126B and 126C at Bluebell Audio - look at Transformers > Interstages. They are exactly the same price as Danbury and probably at least twice as good. Also they are bifilar wound and have a known and stated inductance. Philip at Bluebell is very helpful and knows his tubes.
As for the current to run through the 4P1L, I was shocked to find that in my 4P1L preamp with filament bias I was running less than 2mA through them. I still haven't got to the bottom of why the current doesn't agree with the curves. Anyway, I actually like the sound at low currents - it has thinner mids and more apparent treble but it's very clear. 7N7 who is also working on this project prefers the sound at higher currents because it's fatter in the mids. I use the 126C and I want to set up some kind of rig where I can vary the current through the 4P1L as I listen to it. I'd like my ears to have a say in this, even though the results may be counter-intuitive.
Andy