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Old 7th October 2010, 09:42 PM   #1
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Default Dynaco st70....Can I use 6 ohm speakers?

Can I use 6 ohm speakers? If i can, what port should i use 4 ohm or 8 ohm?
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Old 7th October 2010, 10:06 PM   #2
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If you connect 6 ohm speakers to the 8 ohm tap, you will be reducing the load on the output tubes a bit, providing more output power and more distortion.

Connected to the 4 ohm tap, you will be increasing the load on the output tubes a bit, resulting in reduced power and less distortion. This is a safer option, as the option above may result in red plating the output tubes.

If the DC resistance of the speakers is 6 ohms, they are probably 8 ohm rated speakers, since impedance is a function of frequency (many 8 ohm speakers measure around 6 ohm DCR).

Are the speakers labeled 6 ohms or did you measure 6 ohms with a multimeter?
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Old 7th October 2010, 10:23 PM   #3
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Either will work fine. Try them both, and see if one sounds better to you.
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Old 7th October 2010, 10:24 PM   #4
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Quote:
Originally Posted by boywonder View Post
If you connect 6 ohm speakers to the 8 ohm tap, you will be reducing the load on the output tubes a bit, providing more output power and more distortion.

Connected to the 4 ohm tap, you will be increasing the load on the output tubes a bit, resulting in reduced power and less distortion. This is a safer option, as the option above may result in red plating the output tubes.

If the DC resistance of the speakers is 6 ohms, they are probably 8 ohm rated speakers, since impedance is a function of frequency (many 8 ohm speakers measure around 6 ohm DCR).

Are the speakers labeled 6 ohms or did you measure 6 ohms with a multimeter?
The speakers are labeled and i measured it......The thing is there is only a 8ohm and a 16 ohm tap on this amp cause of the terminals used, i just wanna listen to it a bit......I JUST PICKED IT UP!
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Old 8th October 2010, 11:03 AM   #5
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Are the impedance measurements a result of an impedance sweep with an impedance meter or the nominal posted impedance rating on the back of the speaker? If the speaker is 8ohms nominal for example it could dip to 4 ohms or lower in the low frequency and much higher in the high frequency range. It really doesn't make a hill of beans difference sound wise and isn't going to strain the output stage enough to make a difference either. Pick one and try it it won't go up in a puff of smoke. I ran a pair of Klipsch Cornwall clones which dipped down to 2.0 ohms in the low frequency range off a modified Dynaco stereo 70 without an issue. I had two Dynaco stereo 70's running 4 of these speakers and it did it effortlessly.
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Old 8th October 2010, 04:21 PM   #6
Jim W is offline Jim W  United States
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Quote:
Originally Posted by boywonder View Post
If you connect 6 ohm speakers to the 8 ohm tap, you will be reducing the load on the output tubes a bit, providing more output power and more distortion.
I think this is backwards - the load is reflected back through the transformer, and connecting the same load to the 4 ohm tap would theoretically cut the load impedance at the tubes by half. I agree with everything else you had to say.

Jim
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Old 11th October 2010, 02:09 PM   #7
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Thanks guys..I'm new to this tube stuff..... it was just a temporary thing to use those speakers..... i hooked up my PSB's and there 8 ohm speakers.....Anyway i just picked it up and don't know much about what was done to it.....I can tell it has the updated input board, I gotta take the bottom off it and and see what else was done.... I'll start another thread and have u guy's look at it to see what else was done to it........ I must say it sounds really good and is dead quiet
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