[Paul D. Spiegel]

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?

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

What do RATs think?

- Paul

[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

[Ian Iveson]

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?

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

What do RATs think?

Essentially you'd be connecting one amp to two speakers in
parallel. To retain the design load on the output stage, you
would need to use two 8ohm speakers.

Considering this group is not quite yet pro.test-tone.tubes,
remarks about using speakers with different frequency ranges
are spurious.

Here's a maths exercise. Let's say you have one speaker
that's 4ohms up to 2kHz and infinite impedance beyond, and
another speaker that's infinite impedance below 2kHz and
4ohms beyond. Connect these as you suggest. What is the
resulting impedance for a 1kHz tone? For a 3kHz tone? For a
signal that combines 1kHz and 3kHz equally? For music?

Answers on postcard marked "red herring".

Where's your feedback connected? Assuming you have global
feedback, it would be best connected to a point common to
both speakers. You can't do that with a centre tap
transformer whilst still utilizing all the windings. If the
two secondaries were separate, you could.

Ian

[Big Bad Bob]

On 11/15/10 23:19, Paul D. Spiegel so witilly quipped:
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?

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

What do RATs think?

transformers and beam-power pentodes are expensive. I suggest NOT doing
that. Your total load will be twice that of a 4 ohm load on the 4 ohm
tap because you're loading it TWICE instead of once. The end result at
full power would be pink plates and possible burnt windings. The magic
blue smoke won't go back in, by the way. You'll have to get "a new one"
(whatever blows up first).

You could wire ONE of the speakers on 4-16 but I see no reason why you
would want to. Instead, wire the speakers in series and use the 8 ohm
tap, or (if whoofer/tweeter) use series crossover cap/coil and phase
invert the tweeter.

Or keep on hand a stock of tubes, transformers, filter chokes, and solder.