I have a pair of transformers that purportedly came from one of the Fisher X-100 variants, but I'm not too sure about that. The part number is T781-116-1A. They look about the right physical size for use with 6BQ5s or 7189s, and I plan to use them for the next revision of my "No light District " with a pair of 6P14P-EV outputs. Anyone familiar with the part number? I'm going to throw the transformers on the bench anyway and check them out, but it would be nice to know a little bit more about their pedigree.
I've got a pair, T781-116-1A/2A. My notes say Fisher X-100. The 1A, 2A indicate different lead lengths for right and left channel (or the other way around), I think.
If I remember correctly, the primary wires are blue, blue-white stripe, and red. The red is the HV connection. Secondaries are black, yellow, green and brown. Black is ground/secondary return, yellow is 4 ohms, green is 8 ohms and brown is 16. I'll check tomorrow when I bring the transformer in to work for measurements to make sure,
I have an X100 with 7189 sockets (currently JJ-EL84 w. no problems)
If I remember to look and see OPT part numbers, I'll write them down
or take a photo. Tried 6P14P-EV, but did not sound like the crossover
was biased right. Since the JJs worked without rebias, I just went JJ.
Thats not anything against 6P14P-EV if building from scratch. Mine
certainly did not blow up at scary 7189 style voltages or anything...
Then again, I was watching with white knuckles, ready to yank the
plug if they did... Nothing fatal ever happened.
If I remember to look and see OPT part numbers, I'll write them down
or take a photo. Tried 6P14P-EV, but did not sound like the crossover
was biased right. Since the JJs worked without rebias, I just went JJ.
Thats not anything against 6P14P-EV if building from scratch. Mine
certainly did not blow up at scary 7189 style voltages or anything...
Then again, I was watching with white knuckles, ready to yank the
plug if they did... Nothing fatal ever happened.
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Well, my circuit will look absolutely nothing like the X-100, so I'm on my own as to biasing and everything else. There's even no guarantee that the 6P14P-EVs will even bias up properly per the chart in the spec sheet. I'll have to play it by ear.
Findings with 50V, 300Hz plate-plate excitation plate-plate (Blu - Blu/Yel), Red CT wire left open
4 ohm output (Blk-Brn ) is 1.21V, turns ratio is 41.32:1, impedance 6830:4
8 ohm output (Blk-Grn) is 1.75V, turns ratio 28.57:1, impedance 6529:8
16 ohm output (Blk-Yel) is 2.29V, turns ratio 21.83:1, impedance 7625:16
Primary inductance is 115H plate-plate
4 ohm output (Blk-Brn ) is 1.21V, turns ratio is 41.32:1, impedance 6830:4
8 ohm output (Blk-Grn) is 1.75V, turns ratio 28.57:1, impedance 6529:8
16 ohm output (Blk-Yel) is 2.29V, turns ratio 21.83:1, impedance 7625:16
Primary inductance is 115H plate-plate
As a comparison to the Fisher transformers, here's the numbers from one of a pair of transformers that reportedly came from a Knight 6BQ5 amp. Since they weigh in at 1.5 lb vs. 2.35 lb for the Fisher transformers, I wouldn't expect them to fare as well in the inductance department. Anyway, for 50V, 300V excitation plate-plate;
4 ohm tap (Blk-Yel), 1.147V turns ratio 43.59:1, impedance ratio 7600:4
8 ohm tap (Blk-Grn), 1.666V, turns ratio 30.0:1, impedance ratio 7206:8
16 ohm tap (Blk-Orn) 2.346V, turns ratio 21.31:1, impedance ratio 7268:16
Primary excitation current is 0.605 mA, so primary inductance is 43.9H.
I would pair these guys with smaller 9W tubes like 6AQ5/6005, 6BK5, or maybe a high gm tube like 6HB6 for some Schade feedback (either spectacularly low output impedance or spectacular oscillation). First, though, they get a big scrub-down, as they stink hugely of cigarettes. I hate to think of the room where this amp was stationed.
4 ohm tap (Blk-Yel), 1.147V turns ratio 43.59:1, impedance ratio 7600:4
8 ohm tap (Blk-Grn), 1.666V, turns ratio 30.0:1, impedance ratio 7206:8
16 ohm tap (Blk-Orn) 2.346V, turns ratio 21.31:1, impedance ratio 7268:16
Primary excitation current is 0.605 mA, so primary inductance is 43.9H.
I would pair these guys with smaller 9W tubes like 6AQ5/6005, 6BK5, or maybe a high gm tube like 6HB6 for some Schade feedback (either spectacularly low output impedance or spectacular oscillation). First, though, they get a big scrub-down, as they stink hugely of cigarettes. I hate to think of the room where this amp was stationed.
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