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Old 30th January 2017, 05:27 PM   #1
Miasma is offline Miasma  United States
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Default Tubelab SSE 6ohm OT with 8ohm Speakers?

I just finished building a tubelab SSE. I am very pleased with the results, but my 6ohm speakers aren't quite sensitive enough (~88 dB/m) for my liking (I thought they would be).

What would be the ramifications of running 8ohm speakers (I've ordered frugelhorn3's with fostex fe126en2) on my OT which have a 6ohm secondary?

The OTs I am running are Edcor CXSE25-5K.

I know the reflected impedance would be 5K*8/6 = 6666 which is about 30% higher than recommended. As a result, I think I would see a bit lower distortion, but also a bit less output power?

Should I just suck it up and order a new pair of OTs?

Last edited by Miasma; 30th January 2017 at 05:50 PM.
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Old 30th January 2017, 05:50 PM   #2
Sodacose is offline Sodacose  United States
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I built my SSE with a 5k:6ohm output specifically so that I wouldn't have to worry about 4 ohm or 8 ohm speaker loads. I think you should keep the outputs as is!
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Old 30th January 2017, 05:59 PM   #3
Miasma is offline Miasma  United States
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Originally Posted by Sodacose View Post
I built my SSE with a 5k:6ohm output specifically so that I wouldn't have to worry about 4 ohm or 8 ohm speaker loads. I think you should keep the outputs as is!
Thanks for the reply and encouragement!

I am hoping to get a better understanding of the ramifications of this choice in case I've misunderstood the issue.

I know that speakers are a dynamic load and that nominal impedance does not give a full picture of what the OT and power tubes see.

I'd really appreciate any further insights about what the sonic, OT and power tube impact would be.
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Old 3rd February 2017, 05:19 PM   #4
w5jag is offline w5jag  United States
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Quote:
I know the reflected impedance would be 5K*8/6 = 6666 which is about 30% higher than recommended. As a result, I think I would see a bit lower distortion, but also a bit less output power? .....
The transformation ratio is 625:1 (5000/8). Wouldn't this make 3750 ohms for a 6 ohm load?

Or have I got the arithmetic backwards?

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Old 3rd February 2017, 08:06 PM   #5
Miasma is offline Miasma  United States
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Originally Posted by w5jag View Post
The transformation ratio is 625:1 (5000/8). Wouldn't this make 3750 ohms for a 6 ohm load?

Or have I got the arithmetic backwards?
The transformer is 6ohm, load is 8ohm, so yes I think you have it flipped.
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Old 12th March 2017, 03:18 PM   #6
Atk1d is offline Atk1d  Canada
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Default Similar issue

I have taken my see with 8ohm opt installed. To a friend's house who has 8ohm 200w 3way speakers.
The 6l6 tubes crackle and the elé4 tubes work but when a heavy bass note comes across the speakers sound week almost blown. At higher volumes. Low volume seems to be ok(el34tubesonly)
When the same amp with same opt is connected to my psb t45 6ohm speakers.
All tubes run great,sound is amazing. Listening now. All volume levels

Could the 8ohm load of my friends drivers be faulty? Should I consider dropping the bias resistor from 560? Or increase? To accommodate his speakers, want to give amp as wedding gift but if not going to work on his speakers?
Should be may be update his driver's?

Thanks everyone.
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Old 12th March 2017, 03:39 PM   #7
overtheairbroadcast is offline overtheairbroadcast  Canada
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I honestly don't think that you can compare oranges to socks like that.

Unless the speakers are the same brand and model but with only the 6 vs 8 ohm, then it is imposssible.

My trusty and old adynaco A10 speakers do not sound the same as my friend's trusty and equally old Klipsch Herseys (her speakers are head and shoulders above what I have), and yet both are 8 ohms.

edit: check George's old posts. I think somewhere he had measured what was coming out of an amplifier (or what the speakers were being loaded resistance wise to frequency) and it showed that it is rather dynamic and not static. The swing in numbers is quite the range.

Last edited by overtheairbroadcast; 12th March 2017 at 03:44 PM.
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Old 5th March 2018, 05:58 PM   #8
pitchinwedge is offline pitchinwedge  United States
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Sorry to have to bump yet another an old thread... was/is there a consensus on the preferred choice for the Edcor CXSE25-5K secondary?

At the moment, I have a one pair of 4ohm and one pair of 8ohm "nominally" rated speakers. It's highly unlikely either have totally flat impedance curves. Should I get the 4, 6, or 8ohm secondary?

My limited understanding based on google searches is that if I chose a 6ohm secondary, I'd get more power plus/distortion running my 4ohm speakers, and less power/distortion with the 8ohm.

I've no idea how much practical difference it makes either way so sharing of any experiences would be appreciated!
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