Which B&K ST-140?

OK, I simply have to hear what I'm missing--especially up high--with my old tube gear. After lots of reading on this wonderful website, the B&K ST-140 seems a good quality-vs-cost choice to try.

But which ST-140? The 70w? 105w? only the blue and red one? I only care about which sounds best, especially at the high end.

Thank you!
Hi River251,
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.
How can one distinguish the year of the ST-140's? There is the brown/champagne colored one, the striped one and ?.

The Stereophile article doesn't really tip you off as to which is which.

And regarding durability, which one is the more sound choice? (no pun intended)
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.
Resistive and capacitive load? I have to admit this is over my head.
When would a speaker see a resistive, or a capacitive, load?

Thanks much...took me a while to formulate this question in my mind...

Hello River251,
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