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Grid bias with Class A SE ?
Grid bias with Class A SE ?
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Old 20th April 2008, 03:01 PM   #11
ErikdeBest is online now ErikdeBest  Switzerland
diyAudio Member
Join Date: Mar 2003
Location: Zürich
Another disadvantage is that some high GM valves (mostly are valves designed for series regulation, as the 6C33C, 6AS7, 13E1) are better not to be operated with fixed bias, some datasheet even warn for this. Some solutions I have seen so far:

- bias compensation in this article from Borbely audio about a SE 6C33C http://www.borbelyaudio.com/eb396225.asp
(I think it would actually require some tweaking of the zener value)
- a fixed bias with servo. One possible implementation is given here: http://www.tubecad.com/2005/May/blog0046.htm More recently some micro controller versions appeared on the market, as here http://mennovanderveen.nl/eng/autobias.html
- Morgan Jones has a very ingenious solution presented in his Crystal Palace design. Some day I will copy it (I am gathering the parts...)

my surname is indeed 'de Best': neither misspelling nor snobbism! Ask SY!
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Old 20th April 2008, 05:01 PM   #12
oldeurope is offline oldeurope  Germany
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Join Date: Mar 2008
Default Halbautomatische Vorspannungserzeugung

have a look at this old circuit link.
Comes from link.

Kind regards,
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