Don't buy the ST 140 with the blue and red striping as that does not sound nearly as good.
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The consensus on re/blue vs. gold is mixed. Most opinions I have heard favor the red/blue 105W for sound and ability to drive low impedance loads. Most opinions hold them as only subtly different sounding.
Here's the best part of the link from your post:
"Here is a partial list of amps that have been bettered by the little B&K in my system. Aragon 2004, Hafler Transnova 9300, Meitner STR-50, Sumo Andromada, Counterpoint SA-12, Denon 2200, ASL 1003, and several others I don't recall at the moment."
Curious to know what else was used in those systems that made the B&K come out a winner, but still very impressive...
River251, Speakers have minimal impedance and nominal impedance. One should know not only the impedance swing of a speaker, but also the phase angle before choosing amplification for a given speaker.
What is a low impedance? What is a high impedance? Well, I think that might be very subjective, and many here on Audiogon might have very differing opinions on both. IMHO, in the big picture 6-8 ohms is the middle ground, anything below 4 Ohms is low, and anything over 8 Ohms is high, but there are other important considerations, and speakers ultimately decide.
Phase angles are imperative to tube amplification, but don't effect ss amps so much, Phase angles tell us how far a apeaker dips or rises between resistive and capacitive loads, you can normally see it in an impedance chart, but some ss amps do not have enough ooomph in the power supply to properly handle a 4 ohm load.
I have an B&K EX 4420 in very good shape that I could sell cheap, it would do a good job on most any load. If interested, let me know and I can list it here on Agon, but there are several nice inexpensive amps that would do a good job for you.
I used to own a B&K ST-140 as a backup amplifier. It ran 86dB Magnepan 1.6QRs without too much problem. It was a second generation one - 105WPC, torodial transformer, 2 output devices per channel.
The first generation has a standard frame transformer, while the third has a toroid with 4 output devices per channel.
My experience: much of the "tubiness" actually comes from the cheap electrolytic input capacitor. Once I replaced this with a film (and eventually a more space saving Elna Silmic), lots of the "warmth" went away, coming closer to my (now departed) Threshold S/500.
Yes, when we take a speakers final measurements, we normally see a frequency response chart and a impedance chart. in the impedance chart you will also see a seperate line that measures resistive and capacite load...
This is actually a fairly common practice, many cable manufactures measure cables for resistive and capacitive loads... To put this as non technical as I can: resistance is what it sounds like, it shows how a speaker varies in how hard it is to push within a frequency, Capacitance is a speakers ability to hold a charge at a given frequency...so as frequency varies charts show this curve that goes up and down, as the curve rises, it is going into resistive territory... most tube amps don't mind this, as the curve drops, it is entering capacitive territory, tubes don't tend to like the energy of a capacitive load... Most tubes will tolorate somewhat of a capacitive load. I normally worry when there is a swing of more than 30 or 40 degrees toward capacitive... Take time to look at impedance charts on a few speakers, they aren't hard to find and you will see what we are referring to. I know that i've made this very basic. I hope it makes sense. Tim