SSE/KT-88/Transcendar OPT: UL? CFB? Why? - diyAudio
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Old 9th September 2011, 07:44 PM   #1
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Default SSE/KT-88/Transcendar OPT: UL? CFB? Why?

Hey there,
I just finished my second TSSE build (after the 300B TSE needed to be shelved for now due to some issues I can't fix given my current knowledge level...).

I used:
- Hammond 274BX PT
- 193J choke and ASC motor run cap
- 5AR4
- EH 12AT7 and KT-88
- 5k Transcendar OPTs
- 470Ohm for R17/R27 (cathode res.)
- Auricaps coupling caps

It sounded great out the gate without UL or CFB. As others have noted, amazing low and mid frequency sound (it actually has quite a punch and I am testing with cheap-ish Polk Audio floor standers), but definitely less detail than the first EL34-based I built.

I just hooked up the UL tap and don't hear much of a difference.

Has someone by any chance built a TSSE with similar iron and tubes and experimented with the UL and CFB options? It's easy enough to try, but I am wondering what I can expect with either of these options, and/or with both of them combined.

I also have a pair of UBT-3 OPTs lying around, but they don't seem to be a good match given 450V of B+. George may try them just to see how much smoke they make....

I am not really looking for things that show up only on an FFT Spectrum Analyzer, but mostly for audible improvements. I listen to all different kinds of stuff depending on mood. It could be Charlie Hunter one day and AC/DC the next.

Anyway, I'd be curious to see what other folks' experiments with UL/CFB have resulted in (pointers to other similar discussions I have overlooked are perfectly OK).
Happy Friday,
Stefan
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Old 10th September 2011, 01:27 PM   #2
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Quote:
Originally Posted by dagerman View Post
- Hammond 274BX PT
- KT-88
- 5k Transcendar OPTs
- 470Ohm for R17/R27 (cathode res.)

Has someone by any chance built a TSSE with similar iron and tubes and experimented with the UL and CFB options?
That sounds like my amp. I used the 374BX, and 510 ohm cathode resistors, but otherwise the same. If you search a bit, you'll probably find my thread. Over time and with repeated experimentation, I've chosen to run my Simple with no feedback and triode mode. My Transcendar outputs are slightly older versions, and the UL tap is at 50%. I think he now builds them with the tap at 40%.

Click the image to open in full size.
http://s69.photobucket.com/albums/i4...E/P1100484.jpg
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Old 10th September 2011, 04:17 PM   #3
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Quote:
Originally Posted by Ty_Bower View Post
That sounds like my amp. I used the 374BX, and 510 ohm cathode resistors, but otherwise the same. If you search a bit, you'll probably find my thread. Over time and with repeated experimentation, I've chosen to run my Simple with no feedback and triode mode. My Transcendar outputs are slightly older versions, and the UL tap is at 50%. I think he now builds them with the tap at 40%.

Click the image to open in full size.
http://s69.photobucket.com/albums/i4...E/P1100484.jpg
Thanks Ty. I had picked a 510 Ohm resistor from the table as well, but they are still on backorder at Mouser, so I used 470 for now...
I'll experiment some and see if I can tell any difference in sound with the various options, but may stick with basic triode mode myself, since it already sounds pretty fantastic.
And yes, the newer Transcendars have a 40% UL tap.
Have a good weekend!
Stefan
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