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

Posted by drlowmu (M) on April 3, 2015 at 07:59:22

In Reply to: RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS posted by Paul Joppa on April 2, 2015 at 18:49:52:

Hi Paul,

You show a fine understanding of electronics and you write clearly. I respect that, and do not have that attribute.

The 37 mA. at 250 VDC P-K ( 9.3 Watts dissipation) was simply the Golden Ratio ( 62% ) of 15 Watts, with 15 Watts being the maximum 2A3 plate dissipation rating. I mentioned that low current number to Fender Lover only as an example, but it is NOT at all what I have ever used.

Caucasion Blackplate, in his rush to try to discredit me ANY way he can, seized upon the "lowest" number mentioned, ( and inadvertently perhaps,... so have YOU ! ) without figuring-out what I really liked to employ.

The favored op point of mine was in my description to Fender Lover. In practice, I typically will use 42 mA. on a 2A3, when given free reign to pick the spot.

At 250 VDC P-K, 42 mA. is 10.5 Watts of plate dissipation, or 70 percent of maximum. It is dissipating 8% over the Golden Ratio of 62%. It certainly is NOT operating at 95 to 100% of maximum ( 60 mA. times 250 is 15 Watts, 100% ). The stock SUN SV 2A3, and MOST 2A3 amps running 60 mA. and 250 VDC P-K exhibit a negative-to-my-ear STRESSED SOUND trait, due to thermal issues.

The other thing, ( which I think is totally hilarious ), is that you and Caucasion Blackplate, and MOST other EEs TOTALLY FAIL to ever consider in your analysis is this :

WHERE does the tube operate, on its load line, 90% or more ( 99% ?? ) of the time??

At RMAF shows, LOUDLY playing demanding music (Symphonic Orchestra with Organ), we may reach 3/4s of one Watt. In my home's listening room, ditto, 1/4 of a Watt to 3/4s of a Watt.

CB's graphical load line analysis, and your analysis, is quoting distortion figures at FULL SWING and maximum possible power.

THAT is what BOTH of your analysis' is "all about". Max swing.

I question you two guys, and you TRADITIONAL way of "looking" at audio design. Almost ALL of the time, I am swinging at LESS than full power out, in the linear mid-point on the load line, and at LOW distortion.... BUT..... 42 mA. does NOT sonically exhibit the thermally-stressed "thumbprint" of a 60 mA. bias.

Simply put, my load line SOUNDS NICER, more RELAXED, at normal listening levels we would employ.

If everyone else wants to conventionally design and listen to 2A3 amps with a STRESSED presentation, and burn up the output tubes doing so, so be it. I just simply LAUGH at that !!!

I also must seriously question your impartiality when you describe a 12AX7 as being a non linear tube. If one looks at the characteristic curves, it certainly looks MOST linear to me! Furthermore, it has a RICH proven history of being used in audio devices with State of the Art performance level, for decades in our lifetimes. Think of the ARC SP-3 and SP3A-1, when we were younger, or the highly regarded ARC SP-8.

Now Paul, ALL OF THE ABOVE, ....ALL OF IT...., is just hypothetical engineering gobble-de-gook to me !!!

The proof of the pudding is in the eating. I live in Missouri Paul, the "Show Me" state. "Don't tell me about the pregnancy, just SHOW ME the baby".

Are you coming this year to RMAF 2015, October 2-4 ? If so, look me up and you can HEAR precisely what I am talking about !! Its superb, and beautifully honest to the recorded music. If it sounds good, and is reliable, it IS good !!

Regards and best wishes,

Jeff Medwin , DIY audio amateur .... mostly

Edits: 04/03/15 04/03/15 04/03/15

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