Jj Kt77

Discussion in 'Amps and Cabs' started by Red Planet, Jan 22, 2006.


  1. Red Planet

    Red Planet Member

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    I didnt quite get it on the other thread.

    How do you know if the current draw is too much for your amp before you put em in? I'm speaking of a JCM 800 2203 reissue with a Metro Amps Turret Board HW Kit in it.

    Of all the Tubes I've tried the max I could get was 33ma and had plenty of room to adjust the Bias in the other direction. Does that mean if I stuck em in got a high reading I would have plenty of room to get it down or could there still be a chance of it pulling to much on the OT?

    Does anyone know if the next batch is gonna have a fix on the current draw. I'm thinking of going ahead and placing an order for a set. I want to try out a few more EL34's since I got my Weber Bias Rite.

    Thanx in advance.
     
  2. chuby galoso

    chuby galoso Member

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    red, two diferent isues here. the filament curent draw is a bit higher on the kt77s so you have to know if the filament winding can supply the curent that all the tubes in your amp will draw and you must remember that when you flip the switch for a couple of seconds the fillas will draw even more. this info on what the ampeage is on you mains trans is most of the time not on your schematic. i dont know what the 6.3 winding on your amp can supply but maybe someone out here does. as for the plate curent you can prety well guess that if you are at 33 ma with an average el34 than you will probably read some whare around 50 or even sixty ma each at the same - voltage indused on you input grid. you dont want to run that amp that high even if you like your tubes biased at the high end because you main winding on your power trans also has a limit on the current it can supply. a two tube amp will be around the 200 to 250 ma range and twice that for a four tube amp. but in your case dont worry about exceeding the current of your power trans, just suppl enough - voltage to your input grids to get the current to arond 35 ma per tube. or whatever you like them to pull but not much higher than 40 and no lower than 20. the higher side will sound fatter and the lower side will sound thinner with more crossover distortion. if you crank the dial all the way and cant get the current low enough than you will have to change the value of the resistors that feed your - voltage supply for your input grids and thats asuming that the amp is designed to alow for that and they usualy are. set you meter on the amps scale high enough to handle the current and place the red or positive lead on the bt or center tap of you ot this wire is at your power supply. than clip your - or black lead to pin 3 the plate or anode wires of your ot one at a time. this will show you the current draw at each tube. than take your other meter and set it for dc volts and clip the black to the chassis and the red to any pin #5 of your power tube. this will show you your - bias supply and as you turn the dial you cand see the current change on one meter while you also see what - voltage it takes to create that idle current draw. than when you know what current draw you like the sound ofyour amp the best. than next time you change tubes just go for that current. changing the negative bias voltage is just the means of geting the current draw you want. hope this helps. and no one will know if they can get these tubes to have a lower natural current draw untill the come in and its proven to be.
     
  3. Red Planet

    Red Planet Member

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    Thanx Chuby. So based on what you say and what I was thinking I should have no problems with them. To me the way the circuit is set up from Metro Amps its set to erreor to the safe side. Which could be changed easy enuff but I'm cool with it. I'm gonna go ahead and Place an order for a quad and wait on em.
     
  4. garbud

    garbud Member

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    RP,

    The pin issue that was discussed in the pulled KT77 thread is a real concern so if you are going to use the tubes and they don't fix the pin size problem, then you may want to do the solder deal to the pins that Chuby talked about doing in that pulled thread, or make sure you tighten up those tube sockets. As good as these tubes sound, the sound of the pins arcing in the sockets is not a good thing. I've had to pull these tubes because of that problem, but I will make them work because they do really sound good.



    Garbud
     
  5. Red Planet

    Red Planet Member

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    Didnt someone say the Tube Sockets can be retensioned to fit these dudes? I'll have to check into that.

    I dont think the thread got pulled they usually just lock em down. My guess is DR deleted it. It was his thread. You know you can do that. If you delete the first thread you started a thread with the hole thing is gone. Poof.

    I'd really like to try these Tubes. I love JJ's.To me they are far better quality than the New Sensor (multi level marketting scheme) Tubes going around. (Thats just to me for whomever wants to flame).
     
  6. baron55

    baron55 Member

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    I didn't have any issues with the Pins, they are not hard to push in like some of the current production tubes.

    Power tube sockets are failrly easy to retension
     
  7. chuby galoso

    chuby galoso Member

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    it was only a matter of time before others started to see this problem. yes red you can adjust the sockets and do ok. but dont be putting other tubes in there than putting those back in without re adjusting. why is this a big deal and really pisses me off? if i build a killer hi fi amp and send it out to the custumer with these kt77s in there what do you think the guy is going to do with that amp when he gets it? he is going to spin his 200 gram vinyl on his ten thousand dollar turntable and play around with his colection of tubes to find what he likes best in the amp. thats part of the fun off a tube amp. what am i going to tell this guy? if you plug a real kt77 in there than before you put the jjs back retension you sockets? and the same with playing around with the rectifier tube. i dont want a novice to be sticking a poker in the tube sockets of some thing i built. so i will just flow a little solder out on the pins of the gz34s and the kt77s that jj is making with the to small pins so that i dont have to change a good tube socket to use them.
     
  8. Red Planet

    Red Planet Member

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    I see your point. Makes sense to do that in your case. I wonder why they are changing the sise of em. Cost?
     
  9. rooster

    rooster Member

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    If the 2203 re-issue is a real reissue, and uses the same PT specs as the original, it won't be a problem. Export (to USA) versions of this amp came with 6550's in the USA during the 80's. 6550's pull 1.5A, and I think that KT77 that JJ makes was what, 1.4A on the filaments?rooster.
     
  10. Roccaforte Amps

    Roccaforte Amps Member

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    Any amplifier that can accept EL34's can use KT77's.
    Don't put solder on the pins, bad advice.
    Just retension your socket pins if needed,
    however I do recomend you take it to a tech
    and not try this yourself. You can get shocked.
     
  11. baron55

    baron55 Member

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    The KT77 pulls 1.4 to 1.5 amps at 6.3 V per tube. EL34's pull 1.5 amps at 6.3v per tube. So the KT77 will work fine in EL34 amps. 6L6/5881 tubes pull 0.9 amps per tube, this is where you need to make sure the amp your using (non EL34) can supply enough current to the filaments.

    As for plate current, JJ should have this resolved with the next batch, which is the next run of tubes that will be availible.

    I think the only issue with the tube sockest, if you have an older amp, the sockets are defineately "stretched" I used to always have issues with the SED and older Svetlana tubes, retensioning the tube sockets fixed this issue.

    JJ power tubes ussualy had tube pins that were too large, causing tube sockets to stretch to fit the tubes, then when you went to put something else in, then they were too far apart.

    However, Bob at Eurotubes was sending a little pamphlet with the KT77's telling you to re-tension the tube sockets before installing them, well at lest I got one.
     
  12. chuby galoso

    chuby galoso Member

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    i dont think its cost red. i think they just dont know what they are doing on this. its like alot of things in life. its all in the details. until this recent barage of wrong size tube pins, every tube made be it in europe or the states had the same pins. i have tubes from all over the world and they all fit nice into a stock tube socket. tubes are a forgoton product in the world now. i dont really know but i bet that even in a place like yugoslavia a guy would not need to buy a tube that was just made. i bet he could walk into any tv repair shop and by a tube still in the box from the 40's for his tv or radio. i think tubes are being produced now just for our small industry.
     
  13. chuby galoso

    chuby galoso Member

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    i think he already got shocked when he found out that a rectifier tube has no effect on his tone because its not in the signal path.
     
  14. garbud

    garbud Member

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    baron55,

    I have NOS Cinch tube sockets on a brand new amp. A NOS Mullard EL34 fits real snug. A new re-labeled Mullard fits snugly, vintage GEC KT77's fit snugly, Sovtek's fit snugly, GT's fit snugly. Everything I can throw in the amp fits perfectly snug....except the loose fitting KT77's. I can keep putting the other tubes in and out all day and the sockets never get loose on the tubes. To have to retension the sockets everytime one wants to play around with tubes is ridiculous IMHO. Why can't they use the same pins as EVERYONE ELSE:NUTS. BTW I never got a pamplet with mine and Bob @ Eurotubes never said anything to me about it when I spoke with him, but like I said the tubes sound great until you can hear them arcing.

    Garbud
     
  15. baron55

    baron55 Member

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    Bob had two runs of tubes. I know he had a few at the end of November early December. Then he had another batch of 300 which was the batch I got mine from.
     
  16. GuitarNorton

    GuitarNorton Member

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    I don't give a damn how good the JJ KT-77's sound if they don't use standard size pins I'll never buy them. Seems totally stupid to me.
     
  17. Red Planet

    Red Planet Member

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    Well in the other thread the most anyone stated was measuring a 6 thousanths difference. Now granted I havent had a set or went around measuring pins but .006" aint that much. Now maybe there is something I'm missing here. I do think really to answer all the questions I need to get a set and see for myself. When I do I'll post back about em. I would like to know the deal for sure on the Pins.

    I must say I love JJ Tubes.
     
  18. Roccaforte Amps

    Roccaforte Amps Member

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    JJ is making some of the best current production tubes right now.
    The KT77's are good, but I'm waiting for them to solve the current draw
    and low GM issues they have. I'm told they're working on it, but so far I'm impressed. The pins aren't bothering me at all, in fact their older large pins were a bigger problem for me, I hated those. Doug
     
  19. rastaman

    rastaman Member

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    Just get some and mic them, I have one you can use. That way you'll know if you need to retension/adjust your pins.
     
  20. Red Planet

    Red Planet Member

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    10/4 Dude.

    I have a set of Mitutoyo Digital Callipers but for a really accurate measurement it would be best to use a set of Vernier Micrometers. Sounds to me like there aint a hole lot of difference. One of my other good buddys has an Optical Comparator. We could stick a couple side by side and look at them. He also has a CMM we could make a digital reading of the differences and Transfer em into Master Cam. Ok I'm going over the top now.

    Whats funny to me about this subject is if you take a diameter and change the OD very slightly your only talkin about a couple thousndths per side or so.

    I'm not gonna say one way or the other till I get my hands on a set.

    Rasta maybe we can hook up when I get a set and check em out.
     

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