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Old 16th June 2012, 09:46 PM   #181
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Did you try 6P15P in triode?
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Old 16th June 2012, 09:54 PM   #182
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No, don't have any :-(
What are your impressions about it?
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Old 16th June 2012, 09:59 PM   #183
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Quote:
Originally Posted by mogliaa View Post
No, don't have any :-(
What are your impressions about it?
I like it. Used as a driver in several amps.
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Old 16th June 2012, 10:12 PM   #184
7N7 is offline 7N7  United Kingdom
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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
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Old 17th June 2012, 09:55 AM   #185
mogliaa is offline mogliaa  United Kingdom
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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-c...6/12P17L-3.jpg

Keen to see where people have actually biased this valve and are happy to test this point?
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Old 16th July 2012, 03:32 PM   #186
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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

Last edited by andyjevans; 16th July 2012 at 03:36 PM.
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Old 16th July 2012, 03:46 PM   #187
mogliaa is offline mogliaa  United Kingdom
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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
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Old 16th July 2012, 05:44 PM   #188
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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
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Old 16th July 2012, 05:59 PM   #189
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Quote:
Originally Posted by andyjevans View Post
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
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
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Old 16th July 2012, 06:12 PM   #190
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Quote:
Originally Posted by mogliaa View Post
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.
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