wrote:

Has anyone ever seen this topology covered in any text?
I would like to learn more about how to use it.
What are the benefits, and what's required of the transformer??
I like the idea having the transformer in a feedback loop with the 6550.
Any comments? anyone used it before?

view schematic he

http://www.nashaudio.com/Public/6550_OUT.pdf

Thanks
RonL
I

The connexion shown needs to have the common (gnd) connected to the 4R tap
which is the mid-point on the 16R secondary. By coincidence, I tried this on
a simple PP 6V6 amp (pentode connected) with a Hammond 125E OPT on Sep 9/05.
Here are some results measured with & without this very limited form of
local voltage NFB.

On the 8R connexion the amp internal Z without NFB measured 42.98R, rather
high as one might expect for a straight pentode amp with no FB. With the
simple NFB connected the internal impedance at the same point dropped to
16.62R, otherwise a Damping Factor (DF) of about 1/2.

Would be a useful effect for a guitar amp, IMO.

Cheers, John Stewart