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In Reply to: Re: Please help regarding SET amp choice posted by njjohn on February 14, 2007 at 11:49:09:
Hi njjohnThe 417A (or its electrically equivalent 5842) is an 9-pin, wide bandwidth, low Rp, high-ish gain, IDHT triode that is supposed to present the tunes pretty decently. It is fairly commonly used in phono-stages, line stages, and driver stages of power amps. It has also made an appearance in a spud amp or two. They are popular drivers in DIY amps, where their co$t is less relevant and are suitable for two stage SET amps - Steve Brown, Thorsten and a few others have schematics floating about.
Gordon Rankin of Wavelength Audio uses them as driver stages in some of his amps. IIRC, he like a ~130V plate, 10mA bias (~ -2V at the grid) for these. They can be a b*****d to match between pairs - I think Gordon's designs now use a CCS in the cathode circuit to keep them matched? They have four grid connections and require some effort to prevent RF oscillations...
They sound like a pain in the a*s to use, are becoming expen$ive (especially if your require very close matching), but their reputation for good sound, gain, and low Rp are worth it for some.
Hope this helps
Ultra-consumers: Spending money they do not have to buy things they do not need to impress people they do not like.
Follow Ups:
They are certainly NON linear on their characteristic curve graphs, and can only be used to swing small small signals - to avoid nonlinerarity IMHO.
can get expensive fast. I'd say try a JAN 5687 for $5 dollars,
or something similar as a driver --and save the 417A for phono
stages and the like.
Thanks, that is very helpful.One of the last amps I got from my friend John was a 417a/183. When I had heard it at his house, I was hoping to get it and I did get it shortly after that. It has interesting qualities. It probably would not be my first choice in an amp, but if you have multiple set-ups like I do, then it is something you would want because of the interesting qualities.
I was going to do a post on it at some point. What I observed was almost like an analogy: 300b is to a 45, like a 45 is to the 183 amp here, moving in the direction of reality and pure tone. So being that the 417a is an idht, I might have to rethink my thoughts about idht drivers. They may vary more than I originally thought.
Let me try to describe it. In playing something like John Coltrane's sax, it has a very pure tonal sound. The tonal sound is just riveting, and pure it seems. So it really plays something like John Coltrane sax very well.
The sound doesn't have much width. Kind of a narrow soundstage. Not much bloom or perhaps dimensionality in some ways, but the sound seems more pure than the 45. As the 45 moves more in a realism direction compared to a 300b, this amp surprisingly, seems to outdo the 45 and more towards even more realism and purity.
Since I never had either a 417a nor a 183,I don't know what to attribute to what. I just suspect that the driver has some to do with it, since I know how good WE stuff can be.
Put a better tube (or two) in front of the 183 to really hear something special. I imagine my 183 served as a muse....BTW, my PP 47 uses 417As as input/drivers. Nice tubes but upon reflection I wish I had tried RE134s in front of the 47s.....Perhaps in front of 10Ys or 2A3s in my next amp...
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