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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: RE: Maxing Out my 2A3 amp's Power Transformer posted by Stuben on November 26, 2014 at 06:50:49:
Stuben,
VERY nice post. Even handed. The very first things that my mentor Robert Fulton told me in 1982, about building amps, was as follows - as I recall :
(1) The 2A3 tube is a "direct access to the music" device, and it has very special requirements.
(2) Design the power supply first
(3) Power transformers need to be rated at double the current used in the circuit.
(4) Chokes need to all be "20 Ohms or less" which is hard to find ( 1982 )
(5) a topology of two chokes and two caps in series, as a filter to the finals, is better sounding, smoother sounding, than one choke and cap alone .
(5) The whole amp's B+ should be actively regulated. ( I only regulate the front end in 2014. )
Paralleling windings is one way Stuben, but NOT the best way, to get low Z. The unequal wire lengths produce skewing on sensitive speakers I will use. The best way is to use ONE low AWG winding wire on a big core, so it will all fit in the core's window. I use 950 mA. capable winding wire, ONE center tapped winding.
Do not assume I do NOT use a choke input supply.
The very first device my rectifier tube "sees" is a non critical inductance choke. This mainly strips off RF and junk that a cap input has. With a L1/C1/L2/C2 topology, I can get adequate filtering at C2, where it counts, for triode finals, and the filtering does NOT have to be too low in mVAC. The output transformer's high step-down ratio further assists here.
Low mVAC IS much needed on the amp's front end. There I usually get 2 mVAC or less, and its SHUNT regulated, with one part, a draw-down to ground power resistor.
I will use 50 uF or less for C1 and C2, and any other power supply cap in my amps. High capacitance is NOT your friend with a 2A3, etc. I try to use as little uF as I can. Very often, C1 is 30-35 uF.
Do not get mad at me, but 50 and 60 Ohms chokes to the Finals I have found is quite insufficient from all my 1982-to date sonic testing. I started in at 20 Ohms or less as the "goal" in 1982, and in 2014, I prefer 10 Ohms or less, with really GOOD wires on the leads, in and out. Performance is wonderful this way, you leave a LOT "on the table" employing large L-Critical, over 20 Ohm DCR chokes to triode Finals.
Stay in touch, write to me privately, address above.
Jeff Medwin
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Follow Ups
- RE: Maxing Out my 2A3 amp's Power Transformer - drlowmu 08:16:18 11/26/14 (0)
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