Hi,
this is a question about (internal) tube matching, as well as a question about transformers.
When I want to use a double triode like 12AT7 or 12BH7 to build a low power pp output stage with a center tapped transformer to drive 600 Ohm, there will be some magnetisation from a mismatch in DC current thru the two halves of the primary winding. When I look at a transformer like this
http://www.sowter.co.uk/specs/9041.htm for instance, 500uA are allowed.
Is it save to use a dual triode like the ones mentioned above, with auto biasing thru a shared cathode resistor, without any means to trim the current distribution thru the two triodes? Even with ageing? Even when I run the tube with 2 x 20mA ? (I could add a trimmer or a servo loop with opamps if needed, or just use a different transformer, but I just don't have the right "feeling" and experience yet to know if this is necessary or not.)
JH.
this is a question about (internal) tube matching, as well as a question about transformers.
When I want to use a double triode like 12AT7 or 12BH7 to build a low power pp output stage with a center tapped transformer to drive 600 Ohm, there will be some magnetisation from a mismatch in DC current thru the two halves of the primary winding. When I look at a transformer like this
http://www.sowter.co.uk/specs/9041.htm for instance, 500uA are allowed.
Is it save to use a dual triode like the ones mentioned above, with auto biasing thru a shared cathode resistor, without any means to trim the current distribution thru the two triodes? Even with ageing? Even when I run the tube with 2 x 20mA ? (I could add a trimmer or a servo loop with opamps if needed, or just use a different transformer, but I just don't have the right "feeling" and experience yet to know if this is necessary or not.)
JH.