| pstrisik |
04-21-2016 12:12 PM |
Quote:
Originally Posted by FloridaBoy
(Post 775177)
Peter, you may want to ask Dennis about yours. All the Inspire amps are single ended but not all are triode wired. The single ended pentode amps have more output power than the triode wired amps. There is nothing wrong with either.
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Quote:
Originally Posted by audio bill
(Post 775176)
These amps can be described as SETs since the output tubes are wired in triode mode, but to some purists a "true SET" amp uses actual triode tubes rather than pentodes wired as triodes. I guess it just depends upon how literally you want to define a 'triode' tube.
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Looking through my correspondence, I found this from Dennis (June 2014) that states what I remembered, but didn't remember how I remembered :scratch2:. Confusing is how many different designs he has implemented (this was in response to a question about negative feedback):
Quote:
The Inspire single-ended pentode amplifiers are operating beam power pentode output tubes in a fashion that the tube designers intended. These pentodes were never meant to run in what is called Ultra-Linear mode. The pentode is a higher gain vacuum tube with an additional grid called a screen grid. In order for the screen grid to act in a reinforcement mode of directing the electron flow the potential should be less positive than the plate (anode). If full voltage or more is applied to this screen/beam grid vs the plate it will start to act as the plate. This is what ultra-linear causes. Peter, keep this very important fact in mind about ultra-linear ... UL is a form of degenerative feedback. In simple words UL is a feedback method. The ac audio signal in the primary winding of the output transformer appears on the screen grid in a reverse polarity equating to a lower gain feedback high impedance signal impressed on the screen grid. ... <snip> ... In the Inspire SE pentode design I go a step further toward the original pentode design factor with a low impedance regulated screen-grid B+ power supply. Without a fully regulated screen supply the distortion becomes very high when the tube is pushed. In fact in my design one can run the livin' you know what and still have a listenable experience. Run in UL or without a regulated screen supply at a lower voltage potential than the plate you have all the reasons for discounting pentodes. Pentodes operated in a fashion that the designer of the tubes intended will yield a magnificent sound closer to the recording studio original than a triode in my opinion.. I can go on and on .... I find it so difficult to read the crap that is spewed about triode vs pentode. Either tube will yield a magnificent presentation in pure class A if designed properly. Oh, I definitely use a modest amount of global negative feedback to lower the output impedance of the amplifier. The lower output impedance will allow the low power amp control the loudspeaker drivers. Feed back implemented in a proper fashion is desirable. Speaking of feed-back ... <snip> ... another bunch of marketing hype when I read amps claiming no feedback. When in reality most amps do have feedback in the form of current feedback, degenerative feedback, ultra-linear feedback and local and global feedback.
I better stop before I blow a gasket ... LOL Triode directly heated single-ended class A audio amps offer a bloom in the midrange. Pentode single-ended class A amplifiers offer a full bandwidth with loudspeaker control. I might add the Inspire single-ended class A amps have bass slam and a huge sound stage.
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Quote:
Originally Posted by SteveSem
(Post 775222)
Since this is the most knowledgeable tube group I'm aware of, I wanted to get your opinion on a non-Inspire application. I have a Monarchy Audio NM-24 DAC/Headphone amp that uses 4 6DJ8/6922 tubes. I've had some trouble with Sovtex 6922s that came with it. I am thinking about Mazda early 70s tubes that BrentJes lists on his site for $90 a pair. Any thoughts on these or other suggestions?
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SteveSem - the application is very different, so general tube recommendations may not apply in that particular piece. Having said that, I am very partial to the Russian 6N23P driver - particularly those from the Voskhod plant with the rocket logo from the early seventies. Some say grey (not silver) shields and single wire getter posts are preferable, though this may be internet lore. They are reasonable to buy - typically under $30/pair on ebay - often from sellers in the Ukraine that I have purchased from without problems, though the grey shield, swgp's can run more like $75/pr.
It is 6922 compatible in Dennis' amps, but I don't know if that is true across the board.
That example photo post below is a picture of this tube.
Quote:
Originally Posted by Twanny
(Post 775143)
My amp has no output tube designation in the name. For whatever reason, I can't post pics here.
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You can always upload pics to an image host such as imgur, photobucket, imageshack, etc. and post the link they will provide for forums. Like this:
http://i.imgur.com/PTrk3es.jpg |
