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Old 29th August 2012, 10:10 PM   #11
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In triode, I would think that 200V is the highest voltage for good sound, (and reliability).

With 425V anode, and optimised screen supply/feedback network, I bet it would sound very fine, with higher power output, also.
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Old 30th August 2012, 10:02 AM   #12
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Why not trying it as replacement for 2A3 at 250V/60mA instead of 300B?

If wanting to go higher in voltage a Schade could be a solution.
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Old 30th August 2012, 10:13 AM   #13
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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
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Old 30th August 2012, 10:46 AM   #14
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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.
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Old 30th August 2012, 11:04 AM   #15
Charm is offline Charm  Russian Federation
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Quote:
Originally Posted by andyjevans View Post
You do have to ask the question why no audio enthusiast in Russia ever did anything with these - Russians are pretty clever people.
Register and read:
Search (Поиск) for the word 6P21S (6П21С)
SE 621 - 2 -
http://www.audioportal.su/attachment...7&d=1238269940
621 -
AUDIO DIY
CVC and 6P21S in triode, pentode and second grid.

Last edited by Charm; 30th August 2012 at 11:08 AM.
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Old 30th August 2012, 01:24 PM   #16
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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....
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Old 30th August 2012, 02:00 PM   #17
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andyjevans if this question to me, I do not know English, I use translator.
Radio logs can be downloaded here Радио
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Old 30th August 2012, 02:27 PM   #18
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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"

Last edited by andyjevans; 30th August 2012 at 02:32 PM.
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Old 30th August 2012, 03:21 PM   #19
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Quote:
Originally Posted by andyjevans View Post
Thanks Charm!



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
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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File Type: jpg Schade6P21S.jpg (91.5 KB, 284 views)
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Old 30th August 2012, 03:35 PM   #20
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Hey Rod,
Dont think that one will work with a bifilar IT though.

Will come back with an alternative MJK style Schade-driver.

Anyone got a pentode spicemodel?

Why not go for 250V screen? Think the tube will take that.
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