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Old 16th February 2006, 07:17 AM   #11
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Thank you very much pinkmouse, all!

I'm going to read very deeply the thread, but I recnognize there a "unity gain stage" so far.

Instead I would like to implement a gain stage (a peamplifier with gain from 6 to 10 approx), with a low output impedance.

Any other advice?

Thank you!
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Old 16th February 2006, 12:43 PM   #12
Giaime is offline Giaime  Italy
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Originally posted by EC8010
One solution is to use a Russian 6XS7 double triode, as its unique cathode emissive material based on unobtainium allows complementary operation from inverted supplies. There is a problem in that the cathode is somewhat radioactive (Pu) and there would be a toxicity issue should the fragilium quartz envelope be compromised, but the minor hazard was considered acceptable by the designers. Besides, the problem is not appreciably worse than some of the Western Electric gas voltage references (cf 313C). Because of the complementary operation, the valve must be biased to stimulate electron emission and the lowest noise option is to do this is optically, using a GaAl laser with a wavelength of 465nm pointing directly into the cathode singularity. Obviously, optically stimulated emission requires that the valve (and laser) is enclosed in a light-proof box, and given the minor radioactivity noted earlier, it is advisable to make the box out of pure lead (999 purity minimum). The original application for the 6XS7 was in reactor control systems (cf Chernobyl).
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Old 16th February 2006, 01:22 PM   #13
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Hi Gianmaria,
Bartolomeo Aloia " VTPA the Last".
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Old 16th February 2006, 06:32 PM   #14
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Location: Sweden
The only practical way of doing this using tubes is to copy ideas of DC coupled instrumentation amplifiers. The problems you will encounter is DC restoring and DC drift, DC restoring can be taken care of by using Zenerdiodes and drift must be taken care of by using heavy DC feedback.

I am using a preamp using DC coupled gain stage that I originally designed about 30 years ago. It consist of 2 stages, one for RIAA correction and one for use as a line amp, I think my latest version works very well and it is quite stable. The principal schematic for each gain stage can be seen here

Regards Hans
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