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RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS

Posted by drlowmu on March 30, 2015 at 19:29:11:
Hi Chip,
You obviously have never even HEARD the circuit you disparage, properly executed - that's OK, I forgive you.
NO, you can not Direct Couple the SUN amp with 290-0-290 VAC as the high voltage secondary. I ain't a one-trick pony either.
---------------------------------------------
So, you wanna pick my brain. Fine !
What that SUN SV 2A3 stereo amp DEARLY needs is - TWO things :
(1) A better power supply B+ filter, on several "levels" :
Change the stock B+ filter from a "super crude" C/L/C filter, ( with a NASTY "C" 47 uF ( ooochh, phooey ) ringing input filter and its stock L ( FAR too HIGH in DCR for a 2A3 ).
The SUN needs to use a refined-sounding L1/C1/L2/C2 B+ filter with modern film Cs and two Ls, both Ls small ( under 2 pounds). Ls each measuring under 10 Ohms in DCR... " ultra high fidelity ".
(2) The 2A3 is likely running stock at close to 100% of its 15 Watts plate dissipation, 250 VDC P-K at 60 ( too high ) milliamperes.
Use a more conservative 2A3 plate dissipation, closer to a "Golden Ratio" 62% proportion, The 2A3 will no longer be thermally stressed, and sound stressed. (As always IS the case, the way 90% of the people mis-run 2A3s.)
Hell, number (2)'s easy, changing the stock amp's self bias Rks to two Mills MRA-12s, in each channel.
With a SUN SV 2A3 however, both number (1) and (2) need to be done in conjunction with each other, to get within 5% of the new "optimized" B+ op points. I have figured out HOW to reasonably do that, as the result of many simulations.
Other than the above two changes, the rest of the amp is fine, "for a three stage amp". I have conservatively worked this modification out over the last few weeks. Just need to double check with someone - what the stock SUN amp measures, in four or five places at idle.
Jeff Medwin