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Old 20th April 2008, 03:01 PM   #11
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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...)

Erik
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Old 20th April 2008, 05:01 PM   #12
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Default Halbautomatische Vorspannungserzeugung

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

Kind regards,
Darius
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