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12.10.199.12
In Reply to: RE: Rebuilt Dyna SCA-35 for A-40XL Speakers? posted by David Lawrence on November 01, 2016 at 07:18:01
Sensitivity has to be specified in order to make a good recommendation. However, the A-40XL is a sealed design, which implies not so good sensitivity. I suspect that more power than the 15 or so WPC PP 6BQ5s yield is appropriate. Something with EL34s or 7591s is probably in order.
Eli D.
Follow Ups:
Below: Underside of the SC ASR-433. Lots of Auricaps.
Below: KLH 23 (left), KLH 17 (right)
Below: Faceplate SC ASR-433 with black aluminum knobs.
Maybe enough power.....Maybe not.
I have a pair of KLH-17 speakers that I resurrected with the help of Bold Eagle (Jerry) and they sound absolutely glorious with a 12 wpc Stromberg Carlson ASR-433 driving them. Understand, that the power supply has been significantly upgraded so headroom is most certainly better but, it still only puts out a little over 12 wpc (14.4 wpc in 8 ohms is what the tech measured).
Re-sealing the cloth surrounds with GE 100% silicone bathtub sealant REALLY tightened up the bass. Subjectively, the bass went from a really loose sounding 80 hz. To a mucho tighter sounding low 40ish hz.
I have no idea what the efficiency specs are on the sealed box design KLH-17 are, but they play as loud as I care to listen with a push/pull EL84 integrated.
I guess there's only one way to know - Hook 'em up.
Meat; It's the right thing to do. Romans 14:2
The KLH 17's in their Model 20 alter ego were mated to a "claimed" 15 W/ch in the Model 20 compact system. The model 20 woofer was a 4 ohm version to get a bit more out of the little SS amp; but my recollection was that a Model 20 could play pretty loud.
I used my KLH 17's with a variety of amps; both tube and SS and always felt that 30-35 w/ch was about right. The Dynaco XL speakers used a more sensitive SEAS woofer than the original A25, gaining 2-3 dB for approximately 87 dB sensitivity and pretty close to an Advent or KLH 17.
The real key to unclipped levels is the amp's dynamic headroom. A Stereo 70, for example, on dynamic musical peaks, clips at about 45 w/ch, as does the MC225, and so did the Pioneer SX990 I had at the time.
Jerry
A Stereo 70 (or a pair of Mark IV's) would hit the sweet spot with any of those speakers except the Advent, which was not a tube friendly load, IMO. Of course more power wouldn't hurt, but less power would not work for me.
Dave
A watt or two into even an inefficient speaker is quite loud on average. That's not the problem. The problem is very fast peaks which in classical music can be 20 to 30 dB once in a while. That's 100 to 1000 times the average power. Then your peaks are clipped destroying fidelity there. And if the amp isn't super stable it may oscillate for a short time again hurting fidelity. And worst of all the amp may oscillate at full power at high frequencies which may blow a tweeter. And this is especially true for older tweeters. Modern ones are much more robust.
So too much power(in a good amp) is better than too little. The one plus with a small tube amp is that if driven into oscillation, the clipping is usually less chaotic than a solid state amp making it less dangerous for tweeters.
So what are you doing with the KLH 23s? That was always one of my favorites in the KLH line.
Below: Fisher 500c with 220k (instead of the original 330k) grid resistors, and Russian K-40 coupling caps.
Below: Big slab of wood sitting atop of a antique sewing machine frame.
Fisher 500c and a cheap carousel spinner.
The KLH 23s are sitting atop 3 gallon Redwing crocks at the hunting cabin where the Paradigms (pictured) were.
It's not really a cabin per say as its a year round place. We try to keep it tip top just in case Julian Assange needs a place to hid out if it gets too dicey in England......At least until Trump gives him asylum.
The Paradigm Studio Reference 40v3's are now in my listening room while the crossovers in my horns get updated/modified.
Meat; It's the right thing to do. Romans 14:2
I'd hang out there myself.That would be perfect for old Julian.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
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