Well, the core has to be gapped to work effectively as an SE transformer, so the air gap will dominate the inductance measurement, and the effect of the core will be more second order. If anything, a fancy-pants material like permalloy has a saturation flux density considerably lower than that of silicon steel, so the power capability would be even lower. I think the sweet spot for the WBJ transformers is somewhere between 5 and 10 W. A saturation test would place the operating point more accurately.
Ok, for the weight sweepstakes - the small Transcendar 3k transformer weighed in at 4.1 lb, the WBJ was 5.4 lb including case and potting, the One Electron is 5.4 lb, and the big Transcendar is 5.6 lb. The Quicksilvers are clear winners at ~10lb each. I'll pull one of the Quicksilvers back into the lab tomorrow to check the primary winding resistance - I suspect it'll be pretty low.
I've been sitting on these transformers for ~11 years (a lot of water under my particular bridge), and I think I've figured out what to do with them. I'm thinking of using them with KT120s with a pentode front end and a mosfet follower to drive the grids in a partial feedback "Schade" setup. Recent experience with my updated "Shrine" amplifier have given me some insight. The big question will be whether or not to use any global feedback. I may try both options to see if I can discern the difference with my 68 year old ears....
Congratulations with your “rediscovery” of the Quicksilvers after 11 years! Just in time for a “new Tubelab UNSET”. Sounds like your OTs are perfect for George’s new design that uses a sweep tube as output in cathode-driven configuration. There are a few of us who are currently building amps with the beta boards.
Check here: https://www.diyaudio.com/forums/tubelab/376124-unset-beta-board-build.html#post6762261
Check here: https://www.diyaudio.com/forums/tubelab/376124-unset-beta-board-build.html#post6762261
The new Shrine is another matter entirely - it uses the 7W Transcendar 5k transformers I managed to get before Transcendar got choked up with business. It was a good learning platform for compensation options re partial feedback amplifiers, and I'll be using the wisdom gained from that project on the Quicksilver-based amp. The Shrine is held up waiting for a proper and attractive case. I have some oak board that would make nice side panels, but I need a decent brake/shear combination so I can bend up some aluminum for the top and bottom panels. This amplifier was also a platform for evaluating a SMPS adapter and DC-DC converter scheme for power. The Quicksilver will use a classic line frequency power supply with cold, hard iron. I'll need to find someone that can chrome the power transformer end bell to match the output transformers, or maybe just hide the power transformer.
The question I will have to solve early in breadboarding the new amp is whether I can depend on a feedback-based triode emulation to successfully drive low impedance transformers like the Quicksilvers. Also, I have no idea how the Quicksilvers will look inside a feedback loop. A partial feedback scheme will have an inner loop, as well as a possible global loop. The gain-phase analyzer will tell all...
The question I will have to solve early in breadboarding the new amp is whether I can depend on a feedback-based triode emulation to successfully drive low impedance transformers like the Quicksilvers. Also, I have no idea how the Quicksilvers will look inside a feedback loop. A partial feedback scheme will have an inner loop, as well as a possible global loop. The gain-phase analyzer will tell all...