k12 question

[EWBrown]

Another item concerning the Hammond 1608 and 1609 OPTs, is that the Brown / Blue primary phasing is opposite that of the original kit-supplied UTK OPTs, so connect the "blue" side to where the original instrux called for the brown wire, and vice versa, and for 11BM8 / 16A8s ONLY, the UL SG leads go to their respective tubes.

NB: the UL works best with the 11BM8 and its related tubes, and not as well with the 11MS8 / 10GV8 tubes, as they seem happier with "pentode" mode, as I've found from experience. Last year I built up two of the K-501 / K-12 11MS8 / 10GV8 monoblocks and wired in DPDT switches so that the screen grids could be set for pentode or UL mode, and the UL mode was fairly disappointing. OTOH, the 11BM8 / 16A8 tubes take to UL operation quite well.


16A8 / 11BM8s only: I simply cut the etches that joined all 4 SGs together, right at the tube sockets, and then wired the SG taps directly to the respective solder pads on the bottom of the board.

Follow the instrux for setting up the Hammonds' secondaries for 8 ohms, as provided.

A couple other simple low-cost upgrades: bypass each of the shared power secttion cathode resistors with 100 - 470 uF / 35V, and replace the supplied 33 pF NFB disc ceramic caps with 33pf silver micas.

If you search around this forum under the topics of K-502 and 11BM8, I have posted lots of details about upgrades, mods and experiments with the K-502s and K-12s (and more recently, the new K-16).




/ed B in NH