[Patrick Turner]

On Nov 16, 6:19*pm, "Paul D. Spiegel" wrote:
A common configuration for an output transformer secondary (a la Dynaco)
is C-4-8-16. *The four ohm tap is roughly the mid-point of secondary.

If you connect one 4 ohm load from C-4 and then another 4 ohm load from
4-16, what would the overall load look like to the output stage? *Would
it make a difference if you ground the 4 ohm tap instead of C?

Let me assume you have a pair of full range speakers, each 4 ohms.

The use of a full range 4 ohm speaker across C-4 gives the amp a 4 ohm
load. If anotherfull range 4 ohm speaker is connected across 4-16,
then you have 2 x 4 ohm speakers in parallel and the load is 2 ohms.
Maybe your Dynaco will smoke a bit.

But suppose you have ONE 4 ohm speaker but there is a 4 ohm bass and a
4 ohm treble with separate inputs. You could connect the bass C-4, and
the treble 4-16, and because the bandwidth of each speaker does not
include the bandwidth of the other, then the amp has a 4 ohm load and
is loaded identically to if you had one full range speaker C-4.

When connecting any speaker to C-4, only 1/2 of the secondary winding
is used to produce speaker current so secondary winding resistance
losses are high compared to using say 16 ohms across C-16 when losses
are at the minimum.
By using bass C-4 and treble 4-16, the losses will be reduced
slightly because treble energy is produced by a winding which is
otherwise not used to make power. Because the treble power above 1 kHz
is maybe only 20% of the bass power below 1kHz the use of all the
windings does not reduce winding losses very much, maybe -10% only -
and you will not hear the slightest improvement to the sound.

Patrick Turner.

This could be an interesting way to bi-wire a speaker.

What do RATs think?

*- Paul