Richard explained with EDU/science why the Defy will not like running kt120's, Best stay with 6550/kt88.
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.
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.
28 responses Add your response
I've got a Defy 7 Mkl with 6550's. I wanted to try KT88's but was warned by a Jadis dealer, it's risky on the trans...
^^^^^^^^ 6550 = kt88, 2 labels/same tube. and yes Trejla alrady got word from Jadis Defy accepts 120, which is not any surprise to me. I have no issues with these Svet 6550's. Just that I am looking fora more wider sound stage, for my classical muisc,,I am betting the 120's deliver that superior width and fullness. If only by a hair thin margin. Honestly 88 vs 90 vs 120, we are only talking minimal shades of comparison. Yet our search for a new tweak drives us to try various sets. I can say for sure, all 88's do not sound the same. I found the Svet 6550's a superior sound vs the well respected, highly acclaimed Gold Lion 88's. I've read another comment (audiokarma)supporting my opinion. And from a ebayer, << SEvet 88's matched the GE NOS 88's>> so lets put that <<GE's 6550s best ever 88>> to rest. Furthermore, again taking the OP way off topic, the NOS Svet 6550's (which i sold off cheap 2 yrs ago) are identical to the new Svet 6550's, Exactly identical tube, <<The NOS Svet 6550,,blah blah>> myth is busted , laid to rest. |
Heard back from my friend at Jadis. KT120 tubes present no problem at all in the Defy DA7. Only rebiasing is necessary. ^^^^^^^^^^^^^^^ Jadis is a bit slow in respose, but 100% they will get back to your Q. My hunch was the 120's can be employed in the Defy, The trans are built like tanks. From what i've read on the Unet, the 120's are a superior sound QUOTE: <<in all departments>>> , Just bought the 88's. I over loked cking out the 120;'s. Oh well that project will have to hold off, as my Defy is at Richard's shop, having all resistors swaped out for Takman Rey's,. Its like 50 Rey's and a pair of REX/carbon 18k's. Takman does not stock metal in the 18k so had to go Carbon Film/Rex. Will post YT vid in 3 weeks after upgrade is complete. 120's later next year. |
Thanks a lot Wiebe. I tested the Jadis factory KT88 Gold Lion tubes and have the same experience as you. I have now connected the orange wire on the trafo for 6550-operation and changed for 6550 Winged C. It works good and sounds wonderful, but still, the JA80s eats some tubes. I will test the KT120. |
Hello Calle Jr. These are from 2005 with kt 90 from factory, here you can also set in 6550 without problems. After two weeks playing with the original kt 88 from Jadis, bias was too high, they burn out after 30 hours already, the Dutch importer has bias decreases but problem with all brands was 88 kt at 1500 hours is 50% lot and the rest is worn. The 120 kt is deployed without the bias is increased, is possible (this tube is much more power than a kt 90) And this is the most beautiful sound that my wife and I find we have ever received from a tube. The transformer,s of the ja 80 are themselves less hot with the 120 kt, no matter what and how old the ja 80 is, the transformer is more than heavy enough for the 120 kt. |
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. |
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). |
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. |
Good question Geek. He seems to have a lot of experience in the subject since he owns many Citations and designed his new tube amps around the Citation V. It uses KT 120s. Carver Amps |
Bob Carver told me this when I told him I was afraid I would damage the power transformer using KT 120's in my Citation II: The KT120s are larger, more powerful tubes and pull down about an extra 40 volts. That allows substantially more power. It is true that the KT120s require more filament power, but not enough to even begin overloading the power transformer, especially since you will not increase the plate current at all. Actually you will bias the '120s at a LOWER current than the '88s, and the output transformer will run COOLER than it is now with '88s. Hope this helps, |
As I have stated in a few other threads....the KT-120 is NOT a drop in replacement for the 6550. The KT-120 draws more heater current per tube. Using it could pose a potential risk to the heater winding in your power transformer and/ or make the transformer run hot. Do contact the manufacturer of the Jadis (I have worked on Jadis amplifiers in the past) to make sure that it won't void your warranty or damage the power transformer. You don't want to have to pay someone to replace it. |
I tried contacting Jadis with no response (broken link?), hence I am trying other avenues, even Pierre G. (Canada Jadis Distributor)with no response yet. Checking for possibly any savvy A'goners with the Jadis Defy filament transformer specs/capacity. Thanks Kkurtis for the contact. I will keep trying. |