There has been discussion here about the 6P21S so you might search around.
Here is a good link to triode curves
6P21S triode curves | Bartola Valves
I've used them in headphone amps and pres but not as P-P outputs yet.
Matt
Here is a good link to triode curves
6P21S triode curves | Bartola Valves
I've used them in headphone amps and pres but not as P-P outputs yet.
Matt
https://sites.google.com/site/sever...esevernyjpribojzimafotosessii/usiliteli/6p21s
http://www.etd.su/pdf/206/1/6p21s.pdf
Text in Russian. Try the online translator.
this comes at the right time - I just finished a SET with these in the outputs. they replaced a pair of 300b.
operating conditions:
6P21 is at 424v a-k, -42v, 39mA. Input is 4P1L in filament bias into a 126C interstage, about 13mA, Va 168v, -13.7v.
OPT is LL1682/50mA. I don't know how good this is - I never got great results with it in the past. I always thought the LL1620/80mA was better, which is what
I have in my 300b SET which has the identical input section.
So sound. It regrettably doesn't have the tone of the 300b - doesn't have that lushness or atmosphere. So I'm missing the 300b, which will be put back.
The OPT is a factor, but I don't believe it has that much influence. I'll see when I swap over to 300bs.
Otherwise detail is excellent - as good as 300b if not slightly better. Bass is deep and good. The problem is it starts losing the tone in the midrange - it gets hard
and one-dimensional - not "bad" but not quite comfortable either. It's a bit tiring. And treble is also rather hard.
So, conclusion is it works and has plenty of detail, but the tone is some way behind the 300b. I don't see myself using it unless the problem is with the OPT, which I rather doubt.
I really tried to like this tube, but I'm not getting the sound in a quick-and-dirty experiment.
Andy
operating conditions:
6P21 is at 424v a-k, -42v, 39mA. Input is 4P1L in filament bias into a 126C interstage, about 13mA, Va 168v, -13.7v.
OPT is LL1682/50mA. I don't know how good this is - I never got great results with it in the past. I always thought the LL1620/80mA was better, which is what
I have in my 300b SET which has the identical input section.
So sound. It regrettably doesn't have the tone of the 300b - doesn't have that lushness or atmosphere. So I'm missing the 300b, which will be put back.
The OPT is a factor, but I don't believe it has that much influence. I'll see when I swap over to 300bs.
Otherwise detail is excellent - as good as 300b if not slightly better. Bass is deep and good. The problem is it starts losing the tone in the midrange - it gets hard
and one-dimensional - not "bad" but not quite comfortable either. It's a bit tiring. And treble is also rather hard.
So, conclusion is it works and has plenty of detail, but the tone is some way behind the 300b. I don't see myself using it unless the problem is with the OPT, which I rather doubt.
I really tried to like this tube, but I'm not getting the sound in a quick-and-dirty experiment.
Andy
Andy,
Thanks for that detail. I’ve not used them as power outputs yet. I like a drier sound than 300B so your report is actually encouraging.
In my headphone amp they are running parallel feed---Magnequest Dowdy choke to TL-404 5k/50 ohm taps---6P21 is at 97V a-k, -7v, 12.5mA. My preamp outputs are series feed Electro Print 5K/600 and that setup is about 140V a-k and 18ma I think.
I need to get my Coleman regs on the headphone amp to kill the last bit of hum I have.
Your bass comment is my experience, really nice. But it does have tone and warmth for me, but I’m running them extremely easy. And not to 300B levels of warmth for sure.
Matt
Thanks for that detail. I’ve not used them as power outputs yet. I like a drier sound than 300B so your report is actually encouraging.
In my headphone amp they are running parallel feed---Magnequest Dowdy choke to TL-404 5k/50 ohm taps---6P21 is at 97V a-k, -7v, 12.5mA. My preamp outputs are series feed Electro Print 5K/600 and that setup is about 140V a-k and 18ma I think.
I need to get my Coleman regs on the headphone amp to kill the last bit of hum I have.
Your bass comment is my experience, really nice. But it does have tone and warmth for me, but I’m running them extremely easy. And not to 300B levels of warmth for sure.
Matt
Hi Andy, How have you connected the Screen on those Beam Tubes? They won't like it in triode mode at 424V. In Tetrode connexion, the quality of the screen supply will be crucial.
I suspect that Tetrode mode with 400V anode 200V screen (regulated), and Schade feedback network would be well worth trying. Since you're using interstage transformers, Schade is a really practical solution.
I suspect that Tetrode mode with 400V anode 200V screen (regulated), and Schade feedback network would be well worth trying. Since you're using interstage transformers, Schade is a really practical solution.
I did actually buy 6 and thought of using them in a PP amp to replace 2a3s, or rather 6B4Gs which would be easier. The exercise would only be worthwhile if they sounded better, and I don't think they would. Haven't tried but that's my guess.
I don't see why they won't work at 400v. Screen limit is 200 but in triode it's common to have 150% or 200% higher. This is all guesswork right now - I'd have to actually try them out in a different configuration.
You do have to ask the question why no audio enthusiast in Russia ever did anything with these - Russians are pretty clever people.
Andy
I don't see why they won't work at 400v. Screen limit is 200 but in triode it's common to have 150% or 200% higher. This is all guesswork right now - I'd have to actually try them out in a different configuration.
You do have to ask the question why no audio enthusiast in Russia ever did anything with these - Russians are pretty clever people.
Andy
Andy, please check the link in post 6, for some Russian enthusiasm!
Operating as Triode with excessive voltage will strongly restrict the possibility of good sound. To see why, look at Ale's triode mode curves (link in post 5) - You see that with increasing voltage, the curves are increasingly compressed - and the low-current curves compress heavily at lower current. With a bias of -42V this effect will be severe!
If you look at the WE300B curves, the low-current curve compression also occurs - but only over 400V.
Page 3, top curve:
http://www.westernelectric.com/products/300b/300B.pdf
It's notable that the 300B begins to sound worse as you increase the voltage too much - the 360V nominal operating point was chosen for good reason.
Triode mode at 200V is not much use for a power amp, hence the suggestion of using Tetrode. But this in turn requires some linearising (Schade network) - but may well lead to something that outperforms the 300B.
Operating as Triode with excessive voltage will strongly restrict the possibility of good sound. To see why, look at Ale's triode mode curves (link in post 5) - You see that with increasing voltage, the curves are increasingly compressed - and the low-current curves compress heavily at lower current. With a bias of -42V this effect will be severe!
If you look at the WE300B curves, the low-current curve compression also occurs - but only over 400V.
Page 3, top curve:
http://www.westernelectric.com/products/300b/300B.pdf
It's notable that the 300B begins to sound worse as you increase the voltage too much - the 360V nominal operating point was chosen for good reason.
Triode mode at 200V is not much use for a power amp, hence the suggestion of using Tetrode. But this in turn requires some linearising (Schade network) - but may well lead to something that outperforms the 300B.
Register and read:
Search (Поиск) for the word 6P21S (6П21С)
ñõåìà SE 6Ï21Ñ - Ñòðàíèöà 2 - Ôîðóìû ÀÓÄÈÎ ÏÎÐÒÀË
http://www.audioportal.su/attachment.php?attachmentid=27347&d=1238269940
Êòî çíàåò ÷òî ëèáî î ëàìïå 6Ï21Ñ - Ôîðóìû ÀÓÄÈÎ ÏÎÐÒÀË
Ìèð AUDIO Ýëåêòðîííîå ïåðèîäè÷åñêîå èçäàíèå Ñàìîäåëüíûå êîíñòðóêöèè DIY
CVC and 6P21S in triode, pentode and second grid.
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Hello Charm - that's very interesting. Some 6P21 curves for a start. These says R k-a 360 ohms. That would be between screen and anode?
What's Voldemar saying about 6P21 and 6C4C?
Прошлушивание более 1-й недели SE на 6П21С, нынешний владелец усилителя предпочел вариант именно с ней. Сравнить непосредственно с SE на 6С4С пока не удалось, имхо 6П21С не-настолько и плоха для применения в SE. Вопрос, кто-нить анализировал данные в статье журнала Радио№11,2003г *Спектры гармонических искажений в электронных лампах* Е.Карпова. С уважением Voldemar.
Сам дома слушаю 6С4С,у товарища был SE 6П3С,который переделали под 6П21С.В живую т.е. непосредственно сравнить пока не получается.Хотя чисто субъективно 6С4С звучит лучшее,вариант SE на 6П21С тож не плох.По советам более опытных,сейчас подыскиваю трансы для РР (ради эксперимента мотать не хоца.Имею пару УНЧ *ЗУ-470*,там на выходе стоят 6П3С,думаю попробовать на них.
Sergei seems to be using an operating point of 350v and 47mA. I wish my Russian was better. They seem to like the 6P23.
I didn't know about the Audio Portal - the Russian DIY Audio. There's a 3 page thread on the 6P21 in the first reference you gave, and a 6P21 tetrode amp with 4P1L driver schematic in the second.
Pssbl seems to like it -
Очень хорошая лампочка. Стояла некоторое время у меня драйвером к 300. Легкий подвижный звук, естественный и свободный. Недостаток один - слегка рыхлит бас. Лучше звучит при фиксированном смещении, строже, точнее. Насчет того что 6с4с лучше нее, как-то я не прочувствовал....
What's Voldemar saying about 6P21 and 6C4C?
Прошлушивание более 1-й недели SE на 6П21С, нынешний владелец усилителя предпочел вариант именно с ней. Сравнить непосредственно с SE на 6С4С пока не удалось, имхо 6П21С не-настолько и плоха для применения в SE. Вопрос, кто-нить анализировал данные в статье журнала Радио№11,2003г *Спектры гармонических искажений в электронных лампах* Е.Карпова. С уважением Voldemar.
Сам дома слушаю 6С4С,у товарища был SE 6П3С,который переделали под 6П21С.В живую т.е. непосредственно сравнить пока не получается.Хотя чисто субъективно 6С4С звучит лучшее,вариант SE на 6П21С тож не плох.По советам более опытных,сейчас подыскиваю трансы для РР (ради эксперимента мотать не хоца.Имею пару УНЧ *ЗУ-470*,там на выходе стоят 6П3С,думаю попробовать на них.
Sergei seems to be using an operating point of 350v and 47mA. I wish my Russian was better. They seem to like the 6P23.
I didn't know about the Audio Portal - the Russian DIY Audio. There's a 3 page thread on the 6P21 in the first reference you gave, and a 6P21 tetrode amp with 4P1L driver schematic in the second.
Pssbl seems to like it -
Очень хорошая лампочка. Стояла некоторое время у меня драйвером к 300. Легкий подвижный звук, естественный и свободный. Недостаток один - слегка рыхлит бас. Лучше звучит при фиксированном смещении, строже, точнее. Насчет того что 6с4с лучше нее, как-то я не прочувствовал....
Thanks Charm!
There is a translator on the site - quite hard to understand the translations though. I believe Maximka is saying "it sounded OK until I listened to the 6C4C".
The lamp is a very good, yuzali its output does not sound bad, certainly not compared to the 6s4s, but still a ludshe estate, and the cost in its 60r wins back completely, made another effort to them, was satisfied until I have listened to 6s4s
"звучит не плохо, конечно не сравнить с 6с4с" I think translates "sounds not bad but of course cannot be compared to a 6C4C"
There is a translator on the site - quite hard to understand the translations though. I believe Maximka is saying "it sounded OK until I listened to the 6C4C".
The lamp is a very good, yuzali its output does not sound bad, certainly not compared to the 6s4s, but still a ludshe estate, and the cost in its 60r wins back completely, made another effort to them, was satisfied until I have listened to 6s4s
"звучит не плохо, конечно не сравнить с 6с4с" I think translates "sounds not bad but of course cannot be compared to a 6C4C"
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Here's my Serving Suggestion:
6P21S with passive screen regulation, interstage trafo and ~10% Schade network. Converts what you already have into something that will do justice to that nice looking Filamentary Beamer!
Less time to make this than figuring out what other folks think. When you have an interstage trafo, Schade is so easy.
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