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RE: 300B SE Amp Design: Some Questions

Hi there and thanks for the feedback. To be honest, I really do not know that much about tube topologies and circuits, so the options listed are simply a consolidation of various iterations I came across whilst researching the amp. Pretty much all of them used at least a 3-tube design.

I see the Loth uses a 5965, but also uses a 5687. As to why though I honestly don't know :-( . One thing I did read though was that often the driver tube would not have sufficient power for the 300B, so a voltage amplifier tube is placed in front of it. For example this here: http://www.kta-hifi.net/projects/amp_page/300BEA/300bea.html ; this uses

"one 6J5 (Triode) voltage amplifier, one 6SN7 SRPP driver stage and one 300B per channel."

The 3-tube design seem to use relatively inexpensive tubes, which is most welcome. A tube like the 417A is very expensive which is not preferable.

Also as I came across here: http://www.tubecad.com/2004/blog0011.htm ; it mentions that

"This circuit eliminates power-supply noise from the output, by injecting the same amount of PS noise at the top and bottom of the two-tube cathode follower circuit. The way it works is that the input stage (the first two triodes) define a voltage divider of 50%, so that 50% of the PS noise is presented to the CF's grid; at the same time the 100k resistors also define a voltage divider of 50%, so the bottom triode's grid also sees 50% of the PS noise. Since both of these signals are equal in amplitude and phase, they cancel each other out, as each triodes sees an identical increase in plate current (imagine two equally strong men in a tug of war contest)."

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