After many hours of use, with several pairs of 6K6-GT tubes in the Moreplay, here are my initial impressions of their performance.
First of all, I believe that the Moreplay circuit, and it's operating parameters, is well suited to this tube type. Or maybe, it's the reverse...the tube is tolerant of the Moreplay design. Whatever the case, all the ones I have tried work well. These range from various manufacturers, RCA, GE, Tung-Sol, Sylvania...all original 1940s and later tubes. Some are smoked glass, others clear, you name it. All have slightly different plate structures compared with each other. So without naming favorites, I'd suggest users that want to experiment with this type will not be disappointed in the sound, and your Moreplay will treat you to slightly different presentations, with no duds. All based on my subjective results, so expect a bit of variation.
I initially wanted to try some early G varieties, but could only find one pair, used, that tested fair on my tube tester. They were branded Wards Super Airline, very dark smoked shield, with bottom getters, so I can't say who the maker was. They were nice and smooth, a little rolled off in the highs, but good bass and great definition. No real objection to them, and they look cool, with that ST-14 bulb.
Next up, a pair of RCA NOS clear glass 6K6-GT with black oval plates. One had a date code of 1956, the other was probably a bit older. These were superb, great air but not harsh, midrange just right for vocals, and plenty of clean bass.
Third, a pair of GE clear glass, gray plates, one dated 1964, the other undated, but similar vintage. These were a bit smoother overall, and even more bottom end compared to the RCAs. I almost stopped with these, being very happy with their presentation of a wide variety of recordings.
Fourth, a visually and gain matched pair of Sylvania NOS Clear glass, round black plates with stapled flanges, top getter, yellow print on the bases...production dates not present. These were very close to the GEs for overall sound, a little more top end, and a little less bass. but nothing affecting the overall balance that would make them objectionable. Still very clear and quick.
At this point, any of these NOS tubes would good to go with, very minor differences between them. Not hard to find, inexpensive, and real old-school quality. Get some and try them out! You'll be amazed...at least I was. And the Moreplay is still a great bang-for-the-buck preamp that can hold it's own against anything costing 3 to 4 times the cost. Great design, Bottlehead folks!
Keep up the good work!
--stereo71
