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 Post subject: 6BM8/ECL82 singled ended vs. push-pull comparison
PostPosted: Nov Sat 10, 2007 4:53 pm 
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Location: Newburyport, MA. USA
I'm looking at two different receivers to buy, 1st is a stereo single ended with a pair of 6BM8 ouput tubes. The other is a monophonic unit with a pair of 6BM8/ECL82 in push-pull output. What will the sound quality differences be besides the obvious, 1st being stereo, the other mono.


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PostPosted: Nov Sat 10, 2007 5:07 pm 
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Location: Baltimore, MD, USA
Tough decision. The push-pull will have a lot more output power but no stereo as you noted. So, you decision is what you what do you want to hear, stereo or more power...

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Don


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PostPosted: Nov Sat 10, 2007 5:47 pm 
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I have 2 Lafayette stereo receivers (made by Trio-Kenwood). One has single-ended 6BQ5's and the other has push-pull 6BQ5's. Both have been restored with new tubes, caps, alignment, etc. I have to say that the single-ended model sounds better to me, operating within it's power limits. I won't get into the descriptive phrases commonly used by the audiophiles.

Dave


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PostPosted: Nov Mon 12, 2007 9:27 pm 
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Location: Scandia Minnesota U.S.A.
Drew,

I can only speak of the stereo 6BM8 as thats the only one I have had the pleasure of owning. :)

I have/had a Midland with a pair of 6BM8's in SE Stereo operation and it was a pleasant surprise. With a power output in the 5 watt range dont expect them to shake your house apart, but it had some very nice sound quality.

-Jeremy


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PostPosted: Nov Mon 19, 2007 7:50 pm 
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why will the push-pull set have much more power, both would have two 6BM8s ?


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PostPosted: Nov Wed 21, 2007 6:19 pm 
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Location: Moline Illinois
Hi Drew

I have a 1958 Fisher R-20 that is mono but has 2 output PP tubes, I think el84's. The radio is a console with 3 speakers and the sound out of that thing is as good as any stereo I ever had. Mine has the extra balance controls they call brilliance and something else.

I also recently added a remote speaker to but of course its still mono.

Bruce


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PostPosted: Dec Mon 10, 2007 11:17 pm 
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Joined: Dec Wed 05, 2007 11:08 pm
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Location: Marietta/Moultrie GA
Drew wrote:
why will the push-pull set have much more power, both would have two 6BM8s ?


Mainly, because of three reasons:

1) you can get double the voltage swing, effectively, with two tubes in PP, on the same power supply voltage

2) Even more importantly, you can run the tubes in Class AB1 mode, instead of Class A... this REALLY reduces the idle power dissipation in the tubes, which makes for more "left over" for audio output power.

3) the transformers can be MUCH SMALLER for the same output power in PP, as compared to SE, since they do NOT have to handle DC. This reduces the tendency to saturate... which makes for more power for the same weight of iron. Hence, it's much cheaper to make a 10 watt PP output transformer, than a 10w SE output transformer! This doesn't make any difference really, with regards to the same tubes... but it DOES mean that MOST manufacturers can make units with far more power, for the same price, using PP. This is a DISTINCT motivation for manufacturers!! In addition, not having to have a DC-saturation-blocking air gap in the laminations of the transformers can ALSO increase the magnetic efficiency of the transformer, which WOULD result in more effective power for the same tubes.

Regards,
Gordon.


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