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RE: SRPP/5687 - love it or hate it ?

Posted by GTCharlie (A) on December 9, 2007 at 17:35:34

In Reply to: RE: SRPP/5687 - love it or hate it ? posted by RhythMick on December 9, 2007 at 03:29:31:

Hi Mick. A choke input filter could bring great improvements, BUT do you have enough voltage out of the 2ndary? and/or the rectifier? Supply for input and driver can be adjusted via the dropping resistors, but B+ to the OPT could be iffy (and this could change load-lines). One way to accommodate all that is to locate the power supply (mains transformer, rectification, chokes/caps) in a box separate from the electronics. Another option is to use a choke (say 10Hy/100mA) to decouple the pre/driver from the final stage (instead of the 2k2 or 2k7 dropping resistor). Yet another mod would be to use another transformer to supply the filaments (the 6SN7, the 5687 and the 300B), and unwinding the 2ndary of the present AN transformer (I suspect over 200 DCR), and re-winding for (1) higher voltage to allow choke input filter, and (2) lower DCR for more dynamic response. You can tinker with the 5687 ... but SRPP is a complicated animal, (balancing the push and the pull, and matching impedance) and I'd rather leave it as it is, unless you want to explore parallel or cascaded, etc.... (a note : in a later design, Andy Grove used a parallel 5687, cathode, to 300B). 90 percent of the fun is in the "doing" ...

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