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Hi.Sort of dumb question...Does it justified to use a 12AU7 as CF source than 12AX7 in front of 12AT7 stage or not abolutely necesary,please? I used just 12AX7 till now so that.s the reason I asked for. I wanna know if 12AU7 is justified to be used as CF in front of 12AT7 from driving considerations,please. Thanks
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Last edited by catalin gramada; 09-14-2017, 01:00 PM."If it measures good and sounds bad, it is bad. If it measures bad and sounds good, you are measuring the wrong things." -
Since the CF is a 100% feedback circuit the mu of the tube wouldn't seem to be important. Either an 12ax7 or 12au7 should yield a suitably (and similar?) low impedance output and linearity. The 12au7 is capable of more current. Maybe this would be better if you were using it to drive larger power tubes into class B or something where power tube grid current might place a demand on the driver. Driving a 12at7 I don't think it's important."Take two placebos, works twice as well." Enzo
"Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas
"If you're not interested in opinions and the experience of others, why even start a thread?
You can't just expect consent." Helmholtz -
Thanks Chuck. I don.t know to much about 12AT7 grid current capabilities (my knowledgements are based more on experiments
) but found in my circuits 12AT7 worth not to much if is not drived from a very low impedance source and I wonder if current capabilities of previous stage is not important too from a driving perspective?
Last edited by catalin gramada; 09-14-2017, 01:25 PM."If it measures good and sounds bad, it is bad. If it measures bad and sounds good, you are measuring the wrong things."Comment
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My consideration is only, if you're driving a 12at7 such that it's grid current needs can't be supplied by a 12ax7 CF, you're probably driving it too hard
Maybe in the case of actual power tube types being driven it is more of a consideration. I think Ampeg used 12bh7 (similar to a 12au7) CF's as drivers in their SVT amps. They must have thought this was good enough for driving three paralleled big bottle tubes! So I would think ANY triode type as a CF could handle a single 12at7 grid for current.
"Take two placebos, works twice as well." Enzo
"Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas
"If you're not interested in opinions and the experience of others, why even start a thread?
You can't just expect consent." HelmholtzComment
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Have sense. Thanks"If it measures good and sounds bad, it is bad. If it measures bad and sounds good, you are measuring the wrong things."Comment
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