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SET Asylum Single Ended Triodes (SETs), the ultimate tube lovers dream. |
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SET Asylum Single Ended Triodes (SETs), the ultimate tube lovers dream. |
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In Reply to: Interesting ! ............... posted by Cut-Throat on September 10, 2021 at 17:12:28:
AND ..... Why do you think that this is not widely known, especially with us Low Power Devotees?
That one is easy! I think you're aware of how much care most SET aficionados put into their designs. But how many really high quality low power PP amps have you ever seen? I've been in the business for over 46 years and personally (so this is anecdotal) I can count them on one hand.
So when people are comparing SETs, probably the lowest power PP amp they could get their hands on used either 6V6s or EL84s. In either case those amps probably were not optimized nearly as much as the SETs were in comparison.
One issue is the way the amps make distortion. SETs tend to have a quadratic non-linearity while PP has a cubic non-linearity. But if you have a PP amp with a single-ended voltage amplifier, you get both. This algebraically tends to enhance the 5th harmonic. That gives such amps a harder edge which I think most SET lovers point to as wrong, and I agree with them.
But if you avoid any single ended circuitry and make the amp fully differential, then you get the cubic non-linearity by itself. IOW the even orders are cancelled, but as you increase the order of the harmonic they fall off at a fast rate than seen with a quadratic non-linearity, since distortion isn't compounded from stage to stage in the amp.
The 3rd is treated by the ear the same as the 2nd (its innocuous) and masks the higher orders so such an amp can be nice and smooth, but because its overall lower distortion, also more detailed. Its easy to hear.
Regarding my little EL95 amp, I put up a post about it on the amps and preamps section of this website months ago, maybe even last year. It uses (FWIW) one 12AT7 and a pair of power tubes in each channel. The 12AT7 is wired differentially so each plate is driving the grid of a power tube, and the EL95 is designed to be very easy to drive. A constant current source is used in the cathode circuit of the 12AT7 to linearize its operation and get the most differential effect- its also tied to a -300V supply. Only one grid is used for input; the other is used to receive feedback, which is mostly used to reduce the gain of the amp since its quite linear with no feedback at all. The advantage of doing it this way is there is no IMD introduced to the amp at the feedback node.
The result is a low distortion amp that expresses a nearly ideal cubic non-linearity with good masking of the higher orders. So it sounds very smooth but its also nicely detailed. I used an off the shelf output transformer which was claimed to have 50KHz response; I got full power 100KHz response so that part turned out quite well.
My point of making this amp was simply to build a low power amp that was properly designed and constructed- something I'd not seen in PP amps of that power level prior; they nearly always have some compromise built in on account of being built to a price.
I don't know of such an amp that's actually for sale, although when I designed this amp it was nearly the same price to make 10 chassis as it was to make one, so I can do it again. I'm working on one now that's done in chrome, just for fun.
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Follow Ups
- RE: Interesting ! ............... - Ralph 08:28:52 09/13/21 (5)
- I found your post in the Tube/DIY Forum ............... - Cut-Throat 11:41:20 09/14/21 (3)
- I forgot to mention that amp is class A1 nt - Ralph 13:37:27 09/16/21 (0)
- RE: I found your post in the Tube/DIY Forum ............... - sony6060 12:47:47 09/14/21 (1)
- Not looking for more power as I Bi-Amp................... - Cut-Throat 09:45:57 09/15/21 (0)
- Thank you ! ............. nt - Cut-Throat 11:31:03 09/14/21 (0)
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