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Hi - yep another newbie question! I've searched and think I've found the answer, so apologies for any repetition, but want to be sure its ok.

Will a 16 ohm speaker (specifically a BBQ Blue Dog 50w) work with the Trinity Deluxe...or will one or both blow up!?

Thanks

It will work but not recommended as the tone will change since the reflected impedance back to the tubes will be different . The power tubes will not deliver per design. The Tweed has an 8K / 8 ohm OT, so in this case, a 16 ohm speaker will reflect back 16K to the tubes which will stifle the sound.

Use two in parallel!

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Reflected Impedance

A tube is a high-voltage/low-current (high-impedance) device, while a speaker is a low-voltage/high-current (low-impedance) device. The function of the audio output transformer is to transform the high impedance of the output tube to match the much lower impedance of the speaker. This is necessary to get an efficient transfer of the audio signal to the speaker. The output transformer as an impedance matching device, works on the principal of reflected load. To help explain this, refer to figure 1 below.

To keep the math simple, lets assume an output tube is supplying a 100 volt ac signal to the primary of an output transformer with a 10:1 winding ratio, and the secondary is feeding a 10 ohm voice coil (see figure 1A below). With 100 volts across the primary, there will be 10 volts across the voice coil connected to the secondary. Using ohms law, there will be 1 amp of current flowing in the voice coil.

I = E/R
I = 10/10 = 1 ampere

For further simplification we will assume 100% efficiency in the transformer. Since we have a 10:1 ratio, the current flowing in the primary will be .1 ampere ( 1 amp in secondary divided by 10). With 100 volts across the primary, ohms law tells us that the primary looks like a 1,000 ohms impedance load to the tube.
Z = E/I
Z = 100/.1 = 1,000 ohms

Now if we decrease the impedance of the load, what happens to the impedance in the primary? If we place another 10 ohm voice coil in parallel with the original one, we now have a 5 ohm load (see figure 1B below). Using ohms law again we see that the current in the secondary is now 2 amperes.
I = E/R
I = 10/5 = 2 amperes

This means that the current in the primary also doubles to .2 amperes. Again using ohms law, the impedance of the primary is now 500 ohms.
Z = E/I
Z = 100/.2 = 500 ohms

This is called the reflected load. A 10 ohm load reflects back a 1,000 ohm impedance, while a 5 ohm load reflects back a 500 ohm impedance. The reflected impedance is a function of the turns ratio of the transformer.

from "Radio Remembered"

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thanks Stephen - useful little article; will stick to 8 ohm single 12" for now!

Or else get another 16 ohm speaker, and run the pair in parallel, so you get 8 ohms again.

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Great tones come in small glass jars!

Interesting. What do you mean by "stifle the sound". I have a 16ohm TT Ceramic in my DRRI which has a tap for a 8 ohm speaker. If I change it back to a 8 ohm will that change the sound of the amp?

If you run a 16 ohm speaker on an 8 ohm tap, you will get less power out. You will also get double the usual flyback voltage induced across the OT primary, which could start to approach 1000V or so. Some amp companies such as Trinity, use over-engineered transformers, that can cope with this kind of mismatch and the extra induced voltages. However, this is generally not the case with amps from the larger manufacturers, such as Fender, Marshall, Peavey and Vox, where the bean counters are firmly in control. And when the OT goes pop, there's also some risk for the power tubes and PT. So you're running the risk of having to make some expensive repairs to your DRRI.

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Great tones come in small glass jars!

Does it work the opposite way as well? 8ohm speaker on a 16 ohm tap would get more power out? How would that effect transformer load?

I don't know what it is but I have never been able to wrap my head around how impedance works. It's sad that I've built several amps and I'm still such a n00b.

No, you will still get less power out. With nearly all tube amps, it's a matter of 8 ohm speaker on the 8 ohm output, 16 ohm speaker on the 16 ohm, 4 ohm on... etc....

BTW Matchless' 15W amps are an exception to that rule, as they come stock with an output load mismatch. So you should be able to increase their power output somewhat by putting an 8 ohm speaker on the 4 ohm output, or a 16 ohm speaker on the 8 ohm output.

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Great tones come in small glass jars!

Any idea why matchless does that?

They must think it bring some sort of tonal change about... Maybe I'll try it on my sIII. If I run an 8ohm cab I should be able to run any impedance setting on it without too much risk right?

On my 71 Deluxe reverb I purposely run the amp with a 16 ohm tone tubby alnico. It is a wonderful sounding amp and I haven't smelled any smoke yet. I hope I don't start....

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Guitologist at Large
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