OT Windings

[trem]

I know this gets discussed in one form or another...and I am always happy to read a link(s).
I looked in Merlin's book...the book by Jones (is it Morgan.?) ...and a text book I have. Either it does not get mentioned, or I am missing it.
What effect, if any, do the taps of a multi-tap OT have on the sound coming out of the speaker.?
That is to say ... does the 16 Ohm Tap create a stronger magnetic Field/Flux/Saturation of the OT than does the 4 Ohm winding.?
I am assuming that more windings (16 Tap) concentrates a stronger magnetic field in the core than the 4 Ohm Tap windings do.?
Or is THAT just an effect of the Primary winding, and the secondary just follows along.?
Thank You

[Jazz P Bass]

I can't say about the sound difference.
What I was taught is that for the most efficient transfer of power, the generator (the tubes & the OT primary) must equal the load (the OT secondary & the speaker).
So from the ideal (proper) setup, any deviation will result in a less than optimum transfer of the power.

[J M Fahey]

There is no change in sound.
Each winding is adapted to a certain speaker impedance.
And there is no "more magnetic coupling/efficiency" either.
Higher impedance means more turns, more voltage, but less current.
It all evens out.

They are just "catching" the magnetic energy injected in the core by the primary; nothing more, nothing less.

[Alan0354]

Theoretically, it would change the sound a little because the impedance change will reflect back to the primary. This change the load line of the tube and change the distortion a little. But in reality, I seriously doubt you can hear the difference.

BUT changing to a lower impedance tap than the speaker will lower the power of the amp ( say you connect an 8 ohm speaker to 4 ohm tap) some. I read the wrong color wire ones and connect an 8 ohm speaker to 4 ohm tap, I was wondering why I only get about 16 watt from an amp designed to be about 20W. I even post it here before I found out I read the color wrong on the data sheet. Going back the the correct tap, I got a little over 20W.

[trem]

Theoretically, it would change the sound a little because the impedance change will reflect back to the primary. This change the load line of the tube and change the distortion a little. But in reality, I seriously doubt you can hear the difference.

BUT changing to a lower impedance tap than the speaker will lower the power of the amp ( say you connect an 8 ohm speaker to 4 ohm tap) some. I read the wrong color wire ones and connect an 8 ohm speaker to 4 ohm tap, I was wondering why I only get about 16 watt from an amp designed to be about 20W. I even post it here before I found out I read the color wrong on the data sheet. Going back the the correct tap, I got a little over 20W.

I might be misreading what you are writing, but.....are you talking about mismatching the speaker Impedance to the OT Tap.?
I am wondering about what happens if the Taps are matched.
At any rate.....All else being equal, Is there Any Electrical reason that a series connection would sound different than a parallel connection.?
Thanks

[J M Fahey]

If both speakers are the same (the usual case) , series or parallel is the same because impedance variations, resonance, etc.in one will track the one in the other.

Now if different speakers, mainly different resonance frequency, in parallel one will dampen the other because when one has a high impedance peak at resonance, the other will be much lower impedance, and viceversa, while in series both peaks will develop freely, since the other one in series, being lower impedance, won't do much to affect it.

To say the same in other words: in parallel connections, the lower impedance one will dominate; in series that does not happen.

[Alan0354]

I might be misreading what you are writing, but.....are you talking about mismatching the speaker Impedance to the OT Tap.?
I am wondering about what happens if the Taps are matched.

Yes.

The speaker impedance is reflected back to the primary and become the load impedance of the tube. You change the load, you change the load line and you affect the distortion characteristics. Honestly, I never hear any difference. As I said, you get lower power when mismatch.

[g1]

His question was not about mis-matching. His question was about properly matched OT to load.
If you use 4 ohm tap with 4 ohm speaker, is it tonally any different from using 16 ohm tap with 16 ohm speaker?
I think any differences are slight enough that they will not be noticeable. Some guys argue about the fact that you are using more or less of the secondary winding. I believe that issue was discussed in another thread and the consensus was that there is no noticeable effect.

[pdf64]

'What I was taught is that for the most efficient transfer of power, the generator (the tubes & the OT primary) must equal the load (the OT secondary & the speaker).'

I'm not sure that's the correct way to look at it?
Rather that the output tubes are the source, and the OT primary is the load. The OT just matches the 'real' load of the speaker to an OT primary impedance that best suits the tubes.
The output impedance of regular power tubes (ie their plate resistance) is generally quite a bit higher than the OT primary impedance that gives the most output power.
Audio amps of most types don't conform the maximum power transfer theory, ie match source and load impedance for best power output.
One reason being that output devices don't act as linear resistances.
Another being that it would result in poorly controlled speakers (eg higher fidelity applications).
Another being that there would be lots of heat generated by high power amps (eg PAs).

What applications actually put that max power transfer thing to use? Radio antenna / transmission lines is all I can think of.
The standard example of battery and lamp would result in a battery that wasted half its charge heating itself!

[J M Fahey]

'What I was taught is that for the most efficient transfer of power, the generator (the tubes & the OT primary) must equal the load (the OT secondary & the speaker).'

That's "maximum power output possible" , not "most efficient" , since in that case by definition you are wasting 50% power inside the generator itself.

Different things.

[Alan0354]

I was shown by J M Fahey that matching source and load impedance doesn't work with pentode because the output impedance of pentode is too high, using the load line is mainly to extract the maximum power and/or optimize distortion ( mostly compromise between both). For triode strapped pentode output stage where plate resistance is in 100 to 600 ohm range, then I do see RDH4 match source to load to maximize power transfer. That was given the best match is R_L anode to anode should equal to 2ra of the plate resistance.

[Jazz P Bass]

Got me on that one.

The tube is the generator & the OT primary is the load.
Thanks.

[Malcolm Irving]

There is no change in sound.
Each winding is adapted to a certain speaker impedance.
And there is no "more magnetic coupling/efficiency" either.
Higher impedance means more turns, more voltage, but less current.
It all evens out.

They are just "catching" the magnetic energy injected in the core by the primary; nothing more, nothing less.

Agreed. But I think there is a very slight advantage to using a 16 ohms speaker on the full 16 ohm secondary winding, compared to say a 4 ohm speaker on a 4 ohm tap.

The 4 ohm tap uses half of the secondary turns, so the resistance of the secondary winding being used is half (OK maybe not exactly, depending on which turns are 'on the inside track'). The current when we use the 4 ohm tap is twice what we would have using the 16 ohm tap, for the same speaker power output. Combining these two factors, we find the power loss in the secondary winding when using the 4 ohms tap is 0.5x2x2 = twice what it would be if we used the 16 ohm option.

So using the 16 ohm option, reduces the heat in the secondary winding and allows a tiny bit more power through to the speaker.

[Diablo]

OK, if we carry this further, what about the choice of 4 ohm vs 16 ohm voice coils in two speakers? What are the power implications in those choices. Does one of the VCs get hotter than the other at the same sound output?

[Malcolm Irving]

Interesting question! I think a 16 ohm (reactance) voice coil would only need twice as many turns as a 4 ohm voice coil. (The inductance is proportional to the square of the number of turns). If the same wire gauge is used, that would mean twice the resistance, but half the current, so again 0.5x0.5x2 means half the power loss in the coil.

However, I think the designer would take advantage of this and use a thinner gauge wire (to fit better in the space available), so I expect that would put it back up to the same heat loss as the 4 ohm coil.