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KT120 Tube compatibility w/ Jadis Defy 7 Amp MK 1

Hi, I have an original Jadis Defy I just acquired for I liked its sound very much. However, I don't have any users manual or schematic for the serial #445. Could anyone help by sending a .pdf or electronic copy.

Also, there is a new tube out for the KT88/6550/KT90/EL34 socket line called the KT120. It is the most powerful tube of all of them.

I would like to replace all of the current (12) 6550B tubes with the new larger KT-120 Tubes by Tung Sol (which has a plate dissipation of 60 watts, making it the most powerful tube in the 6550/KT88/KT90 family, or approximately 10 more watts/tube vs. KT90 . Also, when used at the parameters found in existing 6550/KT88/KT90 circuits, the Tung-Sol KT120 is impervious to overload, delivering peak power with extreme reliability and long tube life). Another note regarding universal replacement/compatibility is that the glass envelope of the KT-120 tube is 1/2" taller than other KT88 cousins to accommodate the larger internal plate structure and larger control grid cooling fins, which won't present a problem. However, a word of caution is given regarding the KT120's small increase in current vs. the next most powerful KT88 or KT90 (close in current draw), wherein they say the filament of this tube draws 1.7A to 1.95A, or 0.1 Amp to 0.35 Amp (100 to 350 mA) more current than a KT88 at 1.6 amp; so they say to be safe and recommended to check with your amp manufacturer to make sure the Jadis Defy 7 filament transformer will or can handle the increase in current (at 0.1 to 0 .35A/tube and if you have a quad that is 0.4-1.4A total additional current draw with normal current of 1.6A/tube) without any transformer mods. Will this small increase in current for the Jadis Defy 7 filament transformer be able to handle this increase draw in current required of the Tung-Sol JT120?

Any help answering this technical question would be greatly appreciated and I would gladly pay for a owners manual/schematic for this 100wpc push-pull configured amp design.
bradleys
bradleys OP
3 posts
 
Thanks all. If the 120's are used, what is biasing set at since a lower setting will offset any transformer demand increase?; lower than the normal 4 volts of course, so what would be optimal Trelja?

Doc
trelja
3,223 posts
 
Doc, my experience with Jadis biasing is that when they say "rebias", it is always to the same spec (in the case of my JOR 90 - 120 mv, 110 being the ideal value), regardless of the different (or, even same - EL34, 6CA7, KT77, 6550, KT88, KT90) types of tubes used. My other two Jadis amps are cathode bias, and are "plug and play" when it comes to (a pretty wide range of) output tubes.

They are very cautious to ALWAYS tell you to rebias in their products that have such adjustment. I'm not sure of the Defy DA7 values, but I'm working under the presumption that you have them.
bradleys OP
3 posts
 
Hi Trelja, I will stick with biasing to same recommended voltage regardless of tube type and specs to be safe. Thanks for your Jadis knowledge and input.
wiebe
7 posts
 
Hello music lovers.
In 1990 I bought my first Jadis JA 80 but it was only for el 34 with the old fat philips el 34 in there. (nice). After 2 jears I need new tubes the China el 34 tubes were in one weekend old so I bought tubes from Sylvania 6L6ga jan from 1953(very nice). In 2005 no old stock more. So I bought new Jadis JA 80 with 6550,this was not my sound. (transistor). Next tubes kt 90, I hate them . Next kt88 from Jadis. (nice). Next kt88 from Genalex, yes this is what I want but the kt88 from all concerns are not reliable and live is short about 1500 hour. And there is the new kt 120 I put them in the Jadis and from the first minute yes this is it. I play now five weeks six houres a day with no trouble and the sound on the Wilson Sasha is (live is to short).
skipweasel
20 posts
 
Bradleys,
I was able to get a schematic from Jadis, eventually, for my Defy 7 Mk 2, SN 623. (They said mine is a Mk 2, but it has the larger power transformer and looks like a Mk 3 to me.) The scan they sent me is a little fuzzy, but it is usable if only for a reference while you verify component values visually in your own amp. I've read that they made frequent changes, so it may not be representative of your exact circuit. I would be glad to scan a copy of it to you if you would like. For my SN they recomend 4 to 5 volts bias current per tube, and very importantly, 160mA slow blow fuses. Also, I know for a fact, your main fuse will not blow in an over current situation if you do not have a proper AC ground.
I would be cautious of running more current through any older Defy 7, especially the Mk 1, which I've read runs hot as is. It has been my experience that the design pushes the limits of its passive parts if the bias is left to stray. Owning one of these things can be a great experience if you properly maintain it, unfortunately I think many audiophiles find themselves in deep water with these amps because they are unprepared and uninformed as to what they are dealing with. With a little research, and some DIY skills, I've found this amp to be my lasting favorite over the years. When is the last time someone personally repaired their old Levinson or Krell that you know of?
Happily, I still have my "upgraded" Defy 7 as my primary amp, but I've gone the opposite direction power wise. I'm enjoying it with the "reissue" Mullard EL34s. With my speakers I have yet to run out of power, or even come close. Jadis makes wonderful transformers, and that is one component I would hesitate to risk damaging. Resistors and caps are easy to replace, but if you burn out a tranny, well, that would really suck.
Good luck, and please let us know how it turns out.
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