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Posted by rowuk on
05-20-2014
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fiogf49gjkf0d I ran across this site quite a while ago http://rh-amps.blogspot.de and decided to have a go at building one of Alexs amps. The idea of using a real pentode the way it was originally designed for appealed to me.
I had a chance to get some 307A tubes at a decent price and built the 307A Super. http://rh-amps.blogspot.de/2013_09_01_archive.html
It is safe to say that I am VERY happy. I am listening to more complete works and almost never zap anymore. The amp has plenty of power and that something special that makes you sit down and listen. The sense of "melody" is very good even at the lower range of the contrabass. Since the amplifiers are done, I have identified some other areas in my playback that need attention.
More on the process that brought me to this decision and what it now "after the fact" has fulfilled in upcoming posts.
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Posted by Romy the Cat on
05-20-2014
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fiogf49gjkf0d With my limited experience of using pentodes (primary as phono corrector first stage) I think that the most mysterious in them is power supply of bias to "other" grids. Looking at the Milq schematics it is obvious that I pay too much attention to the bias power supplies and I very much see the difference. With pentodes, which has a suppressor grid and screens, I find the sensitivity of those secondary grids to PS is critical. If somebody did find a good configuration of powering those grids then it would be wonderful.
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Posted by rowuk on
05-20-2014
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fiogf49gjkf0d I have tried the 307A in triode connection in the "standard" no feedback moron 12Axx (in my case 12 AT7) easy configuration with a coupling capacitor and it was "nice". Critical listening was almost impossible, I kept zapping around to find more "impressive" cuts. With Alex Kitics RH concept I have more than enough power (+7Watts?), and very interesting "Sound". Good recordings have a certain "explosiveness" without the etched imaging or mush of the "easy triode". There seems to be some "intelligence" depending on how "thick" the instrumentalist plays. The most important aspect is that I am motivated to keep listening and discovering things not through more "detail", rather by being able to follow the musicians line.
The zeners seem to be one of the key factors to the Sound. I tried a resistor, but the entire presentation changed in the direction of "soft". I can compare this to different trumpets that I own. The RH amp has more core and meat, the triode was big and fluffy but was more like a 3d animation than the space that I have when I am on stage. I just turn on the amp. wait about 5 minutes and listen.
In the past years I have had EL34 and 84s in various configs, a PP config the longest with relatively inefficient speakers. I changed to a 4 way system with horns a couple of years ago and there was a fairly long list of things that I thought could be better that I thought were related to the amplifier - This is the first major step.
Alex Kitic is a very vociferous designer, very convinced about what he is doing - He is very responsive to questions by mail and this venture to get a reference "melody range" for myself has been very good in terms of the sonic results and in getting some independent background behind what I am doing.
It is worth looking through his website. I find plenty of inspiration and because he sells nothing and "gives away" his ideas, there is a credibility that is hard to find anywhere else - except here.......
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Posted by Paul S on
05-20-2014
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fiogf49gjkf0d I once saw a phono stage that used sand diodes, and I have seen an interesting "tank circuit" amp that uses tube diodes +/- like a "buffer". Of recent "popular" amp designs, I have seen a lot of triode PP, but I think this is the first SE pentode I have seen. Now that you know you like it, are you up for DSEP (as opposed to DSET)?
Of resistors, some are softer (or harder) than others. Not suggesting you change anything, but Tantalum can be harder, and the ones like Romy's pre-amp uses can be hard, as well, in certain applications (like the grid, for example). Of course, "hard" is as "hard" does...
Best regards,
Paul S
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Posted by rowuk on
05-21-2014
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fiogf49gjkf0d Yes Paul,DSEP is planned. Actually I have already experimented with it only with the 12" Fane neodymium midwoofer that covers 80-1K and using 1 cap for the low pass filter. I really like what it does. I am comparing how it works with ceramic and neodymium magnets. It is the best that I ever heard ceramic magnet speakers sound.
My comparison right now is with asparagus. It is in season now and pretty easy to cook right, but the sauce if made right, has the density of taste that does not kill the flavor. If it is a cheap sauce mix, there will be even more flavor, but no harmony. The first sense of taste is asparagus, and when I listen to my stereo, it gets that core instrument sound proper and the space around it is the sauce.
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