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Old 15th September 2012, 10:51 PM   #1
cotdt is offline cotdt  United States
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Default Would using a 16ohm speaker damage my SE output transformers?

My OPT has a 4ohm secondary, and I want to hook it up to a 16ohm speaker. Would the high impedance load cause the transformer's magnetic core to saturate and be destroyed?
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Old 15th September 2012, 11:42 PM   #2
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Put an eight ohm power resistor across the outputs in parallel with your 16 ohm speaker. The loadlines for your output tubes are carefully calculated, some say going that far up will make for lower distortion values but straying that far..I wouldn't do it.


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Old 16th September 2012, 12:23 AM   #3
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Try it and see, no harm will ensue. As Rick suggests you can also try various value resistors in parallel with the speakers.

I ran a pair of 16 ohm JBL Rhodes with various SE and PP (0 fdbk) amps and found in the case of the SE amps that I preferred the sound on the 8 ohm taps to the 16 ohm taps, and in the case of the PP amp actually used the 4 ohm taps.

If the speakers are efficient the higher damping factor may be beneficial, just try it and see. Noting that maximum output power will be substantially reduced.
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Old 16th September 2012, 12:42 AM   #4
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to avoid opt damage never operate your amp without any speakers connected....
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Old 16th September 2012, 12:46 AM   #5
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The question might then be "How much load is enough?"
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Old 16th September 2012, 06:22 AM   #6
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The question might then be "How much load is enough?"
Enough so you get the power needed for listening !

Its a balance beween good performance and enough power.
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Old 16th September 2012, 07:41 AM   #7
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So my amp wouldn't self-destruct if I run 16 ohm speakers? What about 25 ohm headphones?
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Old 16th September 2012, 12:05 PM   #8
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I've been running my AKG K601 headphones for years on a number of DIY amps just off the 4 ohm tap. Nothing wrong with the sound, no damage to anything, and volume is plentiful.
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Old 16th September 2012, 12:13 PM   #9
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The loadlines for your output tubes are carefully calculated, some say going that far up will make for lower distortion values but straying that far..I wouldn't do it.
I'm sure they are carefully calculated to get the best compromise between volume and distortion that the designer thought he could make.

However I find that all tubes, including output tubes, operate best with a horizontal load line - that's why I do parafeed with a gyrator on top of every tube. Really makes the OTs job easier, just like having a lot fancier and more expensive OT. Of course then I have to spend money on the caps.

If output power really is paramount, like let's say a PA system, then it would make sense to have a non horizontal load line, to facilitate soft clipping. I for one am happy with my 0.5 watt to 1.25 watt amps even with speakers.
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Old 16th September 2012, 12:15 PM   #10
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When running headphones make sure there is no chance for the HT to reach speaker terminals.

If feedback is taken from secondary winding and a driver tube is shorted, you have a possible injury or at least an unpleasent experience.

Headphones are sensitive devices and what a speaker eat chew and spit out will kill the headphones.
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