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In Reply to: Re: Need help on 2A3 VS 300B differences. posted by DannyB on August 24, 1999 at 05:58:48:
Lower power does not, in itself, necessarily mean lower parts count and/or more "refinement". Parts count is related to how the circuit is realized, particularly how the driver stage is coupled to the output stage. Quality of parts is improtant, and none more so than the output transformer. But the designer's choice of operating points for both the driver and output tubes, as well as the design of the driver stage has the greatest impact on the final sound.Cary amps have consistenly carried published power ratings that are on the high side. The KR2A3 is spec'd at a maximum power output of 3.5W. One way to get more is to drop the primary impedance of the output transformer. The only problem here is lowering the primary Z not only increases power, but it also increases distortion. Another way is to run the output tubes hot and hard, say at the max ratings. Problem here is that tube life is shortend and the Kr are $400/pair.
None of this is to disparage the Cary amps, for they are fine products. I own a Cary 300SEI. But you are paying a lot of money for those slick chassis. There are other options that are less expensive and use better quality output iron than Cary. Check out Wright Sound and Electric Tonalities. The ET offerings can be bought as kits or assembled. both of these companies offer 2A3 amps that are direct coupled, thereby simplifying the circuit over transformer coupled or RC-coupled designs.
check the link below for a little more info on the output tubes.
I'm pretty sure the KR 2A3 is speced at a max of 5 watts.
Jack
Jack, it's spec'd at 3.5W power output with operating points at 300VDC, 55mA. the of course will vary depending on the plate load, which is given as 2.5K to 5K. But as you slide up the primary Z curve power output will decrease. Even at max condition into a 2.5 K load, you are not likely to get more than ~4W. If Dennis squeezes out 5W, the distortion numbers will not be pretty.
Power is a slippery thing.My own amp, which will run either 2A3s or 300Bs (and yes, I prefer 2A3s slightly but I've already lost one at about 500 hours 'cause I run them too hot!), will put out about 6 watts at clipping. That's at 325v and 55mA into a 3000-ohm transformer. The THD is around 10%, and the IM is outa sight - 30% if I remember right.
At 5% THD, it puts out about 3.5 watts. I think of it as a 3-watt amp with 3dB of headroom.
5% used to be a widely accepted reference point; Doc has been quietly on a mission to stick to it but it's very tempting to rate an amp at clipping. In the old days, amp output claims got so wild that laws were passed about how amps are rated. These rules are heavily geared to transistor amps in borderline class B, hence not so relevant to SET amps. But it's a jungle out there, all kinds of wild claims can be found if you actually get out the measuring gear.
Welborne claims 5 watts out of the KR Vs. 3ish out of real 2A3s.
Jack
Dennis says 5 watts. Billy Wright (Cary co-owner) says 4 watts. What's in a watt? :)BillC
just going by the specs. Both Ron and Dennis may have some circuit tricks that get them there. I'm kinda in Doc's camp. Most manufacturers seem to overstate output for obvious reasons. Besides, with the right speakers, like yours, you'll never get out of the first watt or so.
....does have a higher output. 3.5 - 5 watts seems to be what everyone is claiming. Oh, wait not what just anyone is claiming. Rather what some of the leaders in the industry are claiming.
what I read in the specs. I would refer you to Doc's comments about power ratinges and manufacturers claims in the archives.Ron has posted the KR spec sheet at his site which cites a 3.5W output at 300V, 55mA, meaning plate dissipation of 16.5W. Now if you look at the max operating conditions you will see plate dissipation max is 18W, which is obtained at either 90ma and 200V or 350V and slightly over 51mA. There are other conditions of course, but those represent the maixima in current and plate voltage respectively.
It's hard to get and extra 1.5W of power poutput with an incremental increase of the same 1.5 W in plate dissipation. It took 16.5W of dissipation to get the tube to put out 3.5W. I'm not going to say it absolutely impossible to squeez 5 big ones out of the tube, but of what quality and for how long. At $400 per pair, I don't want to run 'em pedal to the metal.
One thing I have noticed about he KR2A3 is that the gain of an amp will drop slightly, but audibly, when you substitute it for a biplate. Note that I said the gain, not necessarily the power, is reduced. I do think that like other KR tubes, the operating points of the amp should probably be optimized when changing to the KR. In some cases the output power can drop very slightly when dropping the KR into a circuit that is set up for lower dissapation than the KR is happy with.The power output of an amp is fairly easy to measure if you have a scope and a signal generator. I don't understand why some folks on this list will defend anyone's power claims (including mine!) without checking it out for themselves.
Hi Phil,Nice post....
Not to drift too far off from the subject, but do you (or any others that want to chime in) have any thoughts on the difficulty level of the ET kits? I just put together the Audio Electronics (Cary) MM phono stage kit (just for kicks), and while I'm no stranger to clippin' and solderin', found it to be a pretty good challenge - a whole lotta parts in a very small chassis. My concern is that some complete novice will get a hold of that kit, and the result will be a sonic mess. While circuit design and parts quality are the two most important considerations in the final sound, sloppy construction and bad part(s) layout can ruin an otherwise desirable finished product.
Thanks,
BillC
I can't see that the Afterglow/Paraglow could be very difficult. Parts layout will be great since it's a Doc/Smoothplate creation. Chassis dimensions are a lot larger that the AES phono stage. The paraSEX is on a smaller chassis, but still shouldn't be that hard. Remember in these direct-coupled two-stage designs total parts count is in the low 20's at most (counting the completed C4S board as one part). Doc's on a mission to get America solderin', so makin' it difficult's not going to further that ambition.
The ParaSEX uses the same chassis as Afterglow, Paraglow, and B-Glow.
or 51-year old eyes. Perhaps I should try sitting farther away from the monitor?;-)
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