My journey of building a tube amp (12AX7 and EL84 SE)

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Looks like close to half the supply voltage is dropped across the output transformer primary , EL84 SE.jpg
 
Looks like close to half the supply voltage is dropped across the output transformer primary , View attachment 120736

@Tubetec you mean for the screen grid? yeah, i have seen this several times already, i asked about it also since my OT has
a tapped primary, but its not marked as such so i dunno what its supposed to be used for if not for the screen grid...

photo_2024-01-11_19-06-49.jpg
 
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No,
the anode supply is dropped by half through the transformer , normally you'd only see 10-15 volts drop across the primary .
 
@Tubetec iam sorry but i dont understand :( you mean here there should be less voltage loss? so there should be about 280V at the anode usually? my OT is dropping too much voltage?
Screenshot from 2024-01-17 13-06-12.png
where do you see 'half the supply voltage, or half anode voltage' ??
 
Ah ok that makes more sense ,
Id go for a cathode bias resistor of 270-330 ohms , you can also add in an extra stage of RC or CLC smoothing off the rectifier ,
 
Ah ok that makes more sense ,
Id go for a cathode bias resistor of 270-330 ohms , you can also add in an extra stage of RC or CLC smoothing off the rectifier ,
ok cool thanks, yeah i will do this filtering in the future probably, but there is no unwanted noise so i think its fine for now..
 
i decreased the bias resistor to 180 to drive the tube a bit hotter because it was suggested by another member, i will probably bring it down a bit again so the tube will last longer
 
hi there, could somebody explain to me the purpose of R16 here? is this a kind of feedback? thank you guys!
it connects the plate from the ouput tube with the plate of the second input stage
Screenshot from 2024-01-23 14-41-36.png
 
hi there, could somebody explain to me the purpose of R16 here? is this a kind of feedback?
Yes, this is negative feedback from plate to plate grid. For instance, the mic pre amp Gates SA70 use this technic, too. (here R4+R8 and C4)

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cool, thank you a lot for the information! i never saw this thing before, only the 'standart kind' of feedback where the output transformer feeds back into the preamp, also i think i never came across this type of negative feedback in any book i read so far, any suggestions on what book i should read that covers this topic? thanks in advance, i really appreciate your help guys, iam a self tought person who tries to figure out stuff, thanks :)
 
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