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Forget the technical summary.......( long )

Posted by drlowmu (M) on August 18, 2007 at 18:22:37

In Reply to: RE: Class A Operation/Bias Points with PP 6B4G posted by Dave Cigna on August 18, 2007 at 09:53:35:

I respectfully say that whatever SOUNDS best, to Fla Charlie alone!, .... is ... "THE" RIGHT answer.

Depending upon how well your system is set up, not just the amp, but the source, the preamp, the wiring, and the speakers ( sensitive or insensitive ) and your listening astuteness, may ( actually, should ) lead YOU to be able to tell what dissipation level sounds the best.

People who don't ever "get it" with speakers, ie, use low sensitivity speakers, will draw 60 mA out of a 2A3, to get MAXIMUM power, or, worse yet, use the less desireable output device alternative to a 2A3 ..ie: a 300B tube. One needs to have a minimum of 94 dB speaker efficiency - to begin to hear some of the differences I talk about, hence, many posters up here do NOT understand what I discuss, or worse yet, wrongfully consider me to be a liar, an idiot, or nefarious...not quite so!

A higher speaker efficiency ( than 94 dB ) is even more helpful with this audio hobby, and so, many of the better builders are better listeners, because they use horn speakers at OVER 100 dB and " hear things " that the lower efficiency speaker listeners never even get to differentiate. ( Designer friends of mine like Dowdy, Jeff Jackson and Fraker ALL use horn systems at home to do their design work, AND..all three fellows use LOW 2A3 bias !! ) So Fla Charlie, this discussion gets lost with a certain portion of the Forum members.

So let me state it all this the drlowmu way:

....................... "Low efficiency IS a very high deficiency." .............. :-)

High efficiency speakers leads one into the realm of both direct-heated triodes and single-ended amplifiers, as only a watt - often way less - will satisfactorily power the system.

My comments on using 45 mA for a 2A3 is based on listening results done with high efficiency speakers and single ended amplifiers, BUT, if you apply what you hear on sensitive speakers, to less sensitive speakers, there can be, and usually is, SOME correlation.

Back to your post. No No NO Fla Charlie, you do NOT increase the voltage across the 2A3 to " make up " for the lower current, and get it back to 15 watts !! Few here have grasped the idea, and it was posted by Dennis last year , under my moniker, and many booed that. You can look it up and get it direct, or I will paraphrase herein:

Fla Charlie, there is a natural order of things in this world. In MANY equipment and operating things, they do best at about 5/8ths of their maximum capability, operate the smoothest and last the longest.

So, for a 2A3, we want to operate it at about 5/8ths of its maximum suggested dissipation, for the most ease in operation. That is 9.375 watts.... and 5/8ths equals 62.5%. Hey folks!!! EVER hear of the Golden Ratio ?? Google It, ask George Cardas. That is where we are at!!!!!!!!!

Fla Charlie, my car is a Chevy and it will run at 110 MPH maximum...but it does best at 5/8ths that, and so does my lawnmower, and so does the power transformer on my audio amp. Its the shape of sea shells, and it occurs over and over again in MANY other naturally good things, perfected by G_D, in this world.

But wait, but wait, it gets better Fla Charlie!! In the Single Ended 2A3 amp, what happens to the output transformer, when the unbalanced current it sees is 41 to 45 mills instead of 60 mills?? Why the output transformer is less stressed and it is operating " deliciously " to use a descriptive and favorite technical and engineering term of mine. :-)

Ask " the maestro magnetics-man " Mr. Mike LeFevre what he thinks of a 2A3 operating though his wonderful DS-025 at 41 mills versus 60 mills, and I believe he will like that operation point a lot better, as to what is going on INSIDE the output trannie !!

Messers Tre', Eli, and Dave Cigna, people who I respect as knowing more technically than me, FAR more, have NOT even mentioned the benefit to the other parts of the whole, when things are operated at close to Golden Ratio proportions, have they?? NO, Tre' and Dave - well they usually don't think that way, although Eli approached it. These are all GOOD GUYS Fla. Charlie, and just maybe - so am I. But, you have to also THINK about how this all ties in together - on that sensitive speaker and Single Ended 45 amp of yours Fla Charlie. That is where, going blindly by the book, or a data sheet, and NOT listening, absolutely SUCKS.

Now, Fla Charlie, I have NOT done TONS of work and listening to operating points near Golden Ratio proportions, but Mr. Dennis Fraker certainly has, he is the master of this. But what little I did on Greg Bradford's home audio system ( My old delicious RCA MI-1428 field coil drivers on my old RCA MI-9595 90 by 40 horns and an Altec 515B bass driver, a two- way ) " told us " all that Gregory and I needed to hear, on how to best bias those Single Ended Globe 45s of his. The lower bias sounded GREAT whereas the bias by the book sounded stressed-out as hell, awful, positively awful versus the Golden Ratio bias. Are you getting my drift, Fla. Chalie, ... and others??

Now, you have a P-P amp and it has a different set of demands upon the power supply, so it WILL be less noticeable, and I do NOT know if you use 98 dB or whatever ? speakers, but at least, now everyone knows from whence I come from.

Also, in fairness, I learned much of this by guidance from Dennis, but in almost all cases, I listened and confirmed things on my own, and he always pans out correct in my set of experiences. Go forward on your own now Fla. Charlie, and blaze new trails for yourself on audio and in understanding and G_d speed.

Jeff Medwin ................. its good to be back..

PS, The " Low Everything " supply can be grafted directly onto P-P 6B4G finals, and is positively sublime, with heavy AWG but high quality wire. You won't believe it. See Wpod's prior post ( URL below ) and comment on the ( piano ) MUSIC, which was his own listening done even BEFORE he got the wire requirement in the ballpark!!

• http://www.audioasylum.com/cgi/t.mpl?f=tubediy&m=124753   (Open in New Window)

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