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In Reply to: RE: Any octal equivalent of 6dj8? posted by DAK on April 30, 2017 at 12:05:11
AFAIK, no. Remember, the 6DJ8, etc. were developed for cascode TV tuner purposes, almost at the very end of new things in tube technology. The "end of the line" was Philips' frame grid, RCA's nuvistor, and GE's compactron. Notice the theme of more "goodies" in a smaller volume. BJTs were making themselves felt, at that time.
Well, i am looking for a driver tube replacement in a SE kt 120 amp schematic.
Are you sure the 'SN7 won't work? Perhaps you can make up the gain difference in the pre-driver.
Buy Chinese. Bury freedom.
I got nothing against the mini tube but it is just not aesthetically pleasing as a 6sn7. Not to mention that i prefer the audio performance of the sn7.
I would not use NFB from the output trans secondary but plate to plate fb from the kt to the driver tube.
I have a small headphone amp by Schiit called the Vali 2, It uses all varieties of the 6dj8/6922 family. Some of the Head-Fi forum guys found a 9 pin adapter for the single 6dj8 to take a 6SN7. This is my present tube for my Vali 2. Its a Sylvania 6SN7-W. This is a hybrid amp and the tube is used in sections for each channel of the preamp. That is a Schiit Modi Multiunit DAC under the amp. ICs, USB and Apple Mini are all Wywires Silver or better
There's nothing wrong with a few dB of global feedback. That's all you'll need for good results with the UL output. I think the 'SN7 will have sufficient gain if you do that. If you're intent on using plate-to-plate FB, I'd consider Eli's suggestion.
Buy Chinese. Bury freedom.
"I would not use NFB from the output trans secondary but plate to plate fb from the kt to the driver tube."
That kind of short loop NFB has a reputation for working best, when the driver is high impedance. The 6AC7 Octal pentode (gm = 9 mA./V.), with regulated g2 B+ and an unbypassed cathode bias resistor might meet your needs.
How about a 7F8 loktal? Dual triode for VHF use. u~48 but gm~3000 so not close to a DJ8 (~12,000) in that regard. Interesting construction on the ones I've seen; the triodes were mounted horizontally at the base so very little structure was visible above the base. Looked empty.
thanks for the tip. Have you made any amps with that tube?
Never made anything that used them in audio app. Bought a pair years ago to experiment and promptly misplaced them. Also, personal experience with repurposed RF tubes such as 6DJ8, 12AU7, 6C4 etc is mixed. As always, YMMV.
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