[quote author="analag"][quote author="emrr"]So, why the voltage divider on the feedback winding rather than the correct ratio? Or, does that simply represent your current state of experimentation within your models abilities?[/quote]
This is an idea, I have been playing with. I believe the correct ratio should be arrived at through experimentation.
This is a simplified version of the design...I would put a pot right after the transformer as rafafredd suggests. I prefer that approach over the variable feedback setup that is more common place in tube pre designs.
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From hearing a good many older circuits, I've had the impression of preferring feedback windings like this over networks between the iron.
I've generally not preferred circuits that followed the input transformer with a pot (usually only seen in older line amps, and now modern preamps), but rather ones that use some sort of interstage pot.
I also like the concept seen in some older Western Electric amps of strapping gain stages in or out depending on need. I've done this in a few four stage 90db type Gates Radio amps, which really helps S/N and overload points when addressed with wildly different levels day to day.