In another thread on this forum concerned with cheap high power transformers originally intended to fire up a high power guitar amp, I speculated about using said transformer to power 813 "Super Schade" monoblocks using a 6AG9 front end. The sticking point was finding some ~5k output transformers that were up to the voltage and current. I just nailed down a pair of Sophia Electric 5.5k output transformers originally intended for use with an 845 SE amp. As such they will be rated for the voltage and the current. Can anyone comment on the general quality of their product?
All joking aside, I'm surprised no one has anything to say about them. The name conjures up thoughts of manufacturers old and exotic. Perhaps I'm thinking of Western Electric. I did a quick search on Sophia, and I assume they are of Chinese origin? The web site does not have a whole lot of history on it. I couldn't find any 5.5K parts on the site, only 3.5K designed for 300B. Am I looking at the wrong page?
Sophia Electric is based near Washington, DC. They may job their exotic tubes out to Chinese vendors as far as I know. They have some rather nice, exotic-looking variants on the 300B, but the prices are rather too rich for my blood. I can buy a lot of 813s for the prices they want. The transformers I got are intended for their line of 845 power amps. People have had good things to say about those amps in the sparse comments I've seen, but I haven't encountered anyone yet who's used just the iron. I could have gone with the special Edcors designed for HV duty, but I just got a patent award and felt like splurging.
I also haven't encountered anyone using Schade -style partial feedback with something as big as an 813, but I see no reason why it shouldn't work. The biggest PITA will be feeding the hungry filaments on the 813s. I may forgo the big bruiser iron in the power supply and go with switchers instead - things are all rather up in the air. It would be a good opportunity to combine an active power factor corrector with a quasi-resonant flyback, which would be a synergistic pairing.
I also haven't encountered anyone using Schade -style partial feedback with something as big as an 813, but I see no reason why it shouldn't work. The biggest PITA will be feeding the hungry filaments on the 813s. I may forgo the big bruiser iron in the power supply and go with switchers instead - things are all rather up in the air. It would be a good opportunity to combine an active power factor corrector with a quasi-resonant flyback, which would be a synergistic pairing.
I have a pair of the 3.5K in my 300B SE amp. No complaints in 7yrs of use. I'd say their performance is on par with some of the better Japanese SE OPTs I've worked with - so quite good actually. I'd rate their subjective performance excellent, quite transparent and uncolored - no real personality of their own. They will handle up to 100mA of plate current and IIRC are better than -1dB 20Hz - 30kHz or perhaps higher, unfortunately no longer have any of the measurement data, I do remember being quite surprised that this amplifier measured about as well as the earlier commercial units which used Tamura Amorphous core OPTs..
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