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In Reply to: For that sake of academics posted by Tre' on March 1, 2007 at 08:31:23:
The bane of writing is things gets left unsaid for the sake of time. I in no way agree in a Universal Constant of 62.5%, it usually takes hunting an pecking to find the 3rd null. A 6CW5/EL86 for example will drop (from memory) about 20 db under some operating conditions. Anyone who has and trusts SEAmpCad can confirm the behaviour quickly. I suspect, though haven't tried, that an 6CA7 will demonstrate a significant 3rd harmonic null at some standing current below 90% dissipation.Could you elaborate on the source of those 300b figures? That's mighty impressive performance. Were those the dominant harmonics? (Not assured for every PP design.)
Follow Ups:
Those are just numbers from the push pull tube cad. 300Bs loaded with about 6.6K. Cathode biased with 430VDC at the plates. And yes, that is assuming complete balance so that there is no even ordered harmonic distortions. Doesn't happen in real life.My only point was to show that running low current in output tubes is usually not a good thing.
Please understand when Jeff says "Run em 5/8ths of Maufacturer's spec" he means 5/8 of manufacturer's suggested operating point. Not 5/8 of max.
In this post
http://www.audioasylum.com/forums/tubediy/messages/117656.htmlJeff says "Of Maufacturer's $ugge$ted operating point$, and NOT max points at all."
That's just crazy. A 300b with only 37.5ma of current. There will be very little power and very high distortion.
I don't think Jeff really understands audio electronics. He just talks like he does. And speaks as if in decrees from above.
"you must have low DCR in your power supply or your system is Lo-Fi""All output tubes sound better if they are run at 5/8 of suggested operating point"
"The value of a grid stop resistor is critical to .01 ohm"
The thing is, people seem to listen to him. I'll never understand why.
Tre'
P.S. Those numbers for the 300b are impressive. But take some time to look at the plate curves for the 300B. It's a very linear tube. The 2a3 is better and the 45 even better. The 45 is near perfect. Loaded right you will get almost no distortion from a 45. It's the lowest distortion amplifying device ever made. I wish I has some really good horn speakers. I don't so I use 300b's to get some power going.
Hey man,YOU have NOT listened to ANY of the points I have been called on to the matt - as being no good - in your above post.
I HAVE LISTENED to ALL of the above, UNlike you!! I know that what I contribute up here comes from listening experience and it sounds superior, even though you do not comprehend it academically - and you never will. I don't care about academics, if the stuff doesn't perform really well according to ear !
How about adding to the above list "reaching critical inductance at 120 HZ" ! Ha, what a sonic crock, now disproven.
And who CARES about 300B distortion figures?
What a way to whack off, when a 45 or 2A3 will sonically creme a 300B?? The bottom line ( and summary ) on 300Bs remains - that 300B users are ONLY for those people "who don't get it" with speakers, and use not-high-enough-efficiency speakers. People just like you.
Thanks again for the extended reply. Many DHTs have beautiful curves but I don't recall ever seeing ideal PP distortion figures for the 300. The discussions usually centres on SE. It's a real eye opener. Regarding recommendations of the absolute and specific type you mentioned, let's just say they don't hold much attraction.
Thx again!
You're very welcome. If you haven't yet, check out Lynn Olson's website.I think he has some very good things to say. He's a bright guy.
You need to dig for it, but the paper entitled "Amplifier Design Philosophy" is a good overview of what I think makes for a good amplifier.
It's at the very end of the "The Amity, Aurora, and Karna" section.
http://www.nutshellhifi.com/triode4.html
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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