I am curious how the KT120 tube sounds. I want to try making an amplifier with a pair. Here is a link to the curves. I am having trouble judging which graph is the ultra linear, as they are not labeled. The first one looks like it maybe a triode connected. The third could be the UL graph.
http://www.newsensor.com/releases/KT120TungSol-Curves.pdf
A KT90 is another option, the datasheet does not have UL curves either.
http://www.newsensor.com/releases/KT120TungSol-Curves.pdf
A KT90 is another option, the datasheet does not have UL curves either.
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Just finished a p-p amps with the use of EL34 or KT120.
Good results, mainly in tetrode connection.
With 440 Vdc and 100 mA of bias for each KT120 (45 w anode dissipation) we got 50 wrms on 8 ohm and, until 25 w, it is in class A.
The distortion is very good; the phase splitter uses the ECC99.
With a particular out. trafo (3 ohm on secondary and 3200 a-a to primary) we measured about 72 w on 4 ohm (as mentioned, we got 50 w on 8 ohm).
I am preparing an article on an Italian magazine; in case I can send details.
Ciao
Walter
Good results, mainly in tetrode connection.
With 440 Vdc and 100 mA of bias for each KT120 (45 w anode dissipation) we got 50 wrms on 8 ohm and, until 25 w, it is in class A.
The distortion is very good; the phase splitter uses the ECC99.
With a particular out. trafo (3 ohm on secondary and 3200 a-a to primary) we measured about 72 w on 4 ohm (as mentioned, we got 50 w on 8 ohm).
I am preparing an article on an Italian magazine; in case I can send details.
Ciao
Walter
Those KT120 plate curves given in the Rohren-Nach-.... link sure aren't very reassuring. Worst I've ever seen.
http://www.jogis-roehrenbude.de/Roe...rstellungen/BTB/KT120/KT120TungSol-Curves.pdf
http://www.jogis-roehrenbude.de/Roe...rstellungen/BTB/KT120/KT120TungSol-Curves.pdf
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Can´t make the Reply tools work for some reason.
These curves aren´t impressing either:
http://www.revintage.se/KT120sofiaT.PNG
http://www.revintage.se/KT1202P.PNG
These curves aren´t impressing either:
http://www.revintage.se/KT120sofiaT.PNG
http://www.revintage.se/KT1202P.PNG
Are all these jaggie kinks maybe an artifact of the curve tracers used? Lack of density of sampled points, or some psuedo random digital selection of the measurement points to avoid over heating the tube. So adjacent points are taken at different internal temps of the tube?
Could be some HF oscillation issue in the tube/tracer jig. I use stopper resistors and/or ferrite beads on the tracer pin leads (g1, g2 and plate) to avoid that.
Or maybe there is some hysteresis issue with this tube when traced with increasing plate voltage versus decreasing plate voltage. I have seen this hysteresis issue around the knees on some pentodes on my TEK tracer. But the kinks in all of the KT120 curves seem to be everywhere.
Another issue I see sometimes is decreasing emission or gm during a curve trace that seems to gradually collapse the higher current curves after I throw the tracer switch. Reversible and repeatable after letting the tube cool down again. Not sure if its due to emission dropping or some grid heating up.
Could be some HF oscillation issue in the tube/tracer jig. I use stopper resistors and/or ferrite beads on the tracer pin leads (g1, g2 and plate) to avoid that.
Or maybe there is some hysteresis issue with this tube when traced with increasing plate voltage versus decreasing plate voltage. I have seen this hysteresis issue around the knees on some pentodes on my TEK tracer. But the kinks in all of the KT120 curves seem to be everywhere.
Another issue I see sometimes is decreasing emission or gm during a curve trace that seems to gradually collapse the higher current curves after I throw the tracer switch. Reversible and repeatable after letting the tube cool down again. Not sure if its due to emission dropping or some grid heating up.
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tried the kt-120 and then some...
Hola, here's my first shot at the kt-120. This is a SET based loosely on Michael Abdullah's KT-88 schematic. This is on 3 seperate chassis with Edcor 6 Ohm only output trannys (built specifically for my Klipsch Kg-4...I'm a freak) and a seperate dual power supply. The supply is of my own device and is a funky split transformer dual power supply. It's using a pair of 5u4gb ea on it's own half of the primary which is split between two non-ct transformers. It's a quirk of that's what's what was available at the time cheap ($10 ea for the power trannys) but they give the unusual consequence of a cascaded dual switched power supply. Switching the primary current to either (one half of the full primary) fully energizes that heater and allows full conductance of that half of the full virtual ct primary. Once this happens, the other heater eventually sees full heater voltage while both are only putting out 1/4 plate voltage. Thus it's a funky soft-start based purely on the geometry of the components and you can switch either switch on first...pretty cool!!
SET :: KT-120 SET based loosely on Michael Abdullah's KT-88 SET's picture by billfellman - Photobucket
And here's my cloned version of it with all toroidal xformers and SS power supply:
SET :: KT-120 SET amp, Toroids picture by billfellman - Photobucket
Hola, here's my first shot at the kt-120. This is a SET based loosely on Michael Abdullah's KT-88 schematic. This is on 3 seperate chassis with Edcor 6 Ohm only output trannys (built specifically for my Klipsch Kg-4...I'm a freak) and a seperate dual power supply. The supply is of my own device and is a funky split transformer dual power supply. It's using a pair of 5u4gb ea on it's own half of the primary which is split between two non-ct transformers. It's a quirk of that's what's what was available at the time cheap ($10 ea for the power trannys) but they give the unusual consequence of a cascaded dual switched power supply. Switching the primary current to either (one half of the full primary) fully energizes that heater and allows full conductance of that half of the full virtual ct primary. Once this happens, the other heater eventually sees full heater voltage while both are only putting out 1/4 plate voltage. Thus it's a funky soft-start based purely on the geometry of the components and you can switch either switch on first...pretty cool!!
SET :: KT-120 SET based loosely on Michael Abdullah's KT-88 SET's picture by billfellman - Photobucket
And here's my cloned version of it with all toroidal xformers and SS power supply:
SET :: KT-120 SET amp, Toroids picture by billfellman - Photobucket
1st prize for ugly curves goes to EL/PL 504. At least Philips or any other never claimed it was intended for audio use. I think that KT90 is a EL504 derivative, too.
Thanks for your informative reply...I caught that posted a few entries before, also. The proof is in the pudding though. They sound awesome. And I've heard a lot. I'll scope them and post the results as soon as I get the chance. In the meanwhile, this little smiley-face will have to do as a representation of how well they perform. 
cheers, Bill
cheers, Bill
Hmm. Guess I've been in the dark- just found out these tubes today. So I naturally looked here at DiyAudio to see if peeps have been playing with them...
Revintage- those curve links you posted are made by the Sofia Curve tracer. I have one. If you run un-shielded patch cables out a bit and you're doing curves on sensitive tubes, you could get artifacts like those. Possibly picking up RF noise? Or there could be an issue with their Sofia.
Sample rates are selectable in 5, 11, or 22 points per curve.
I was running curves on the WE 448A and saw the same effects as I was using an adapter with un-shielded wires.
Pic attached with 448A curves showing similar anomaly. I've only seen this effect with this tube, most likely because of the lack of it's adapter socket shielding.
-Kent
Revintage- those curve links you posted are made by the Sofia Curve tracer. I have one. If you run un-shielded patch cables out a bit and you're doing curves on sensitive tubes, you could get artifacts like those. Possibly picking up RF noise? Or there could be an issue with their Sofia.
Sample rates are selectable in 5, 11, or 22 points per curve.
I was running curves on the WE 448A and saw the same effects as I was using an adapter with un-shielded wires.
Pic attached with 448A curves showing similar anomaly. I've only seen this effect with this tube, most likely because of the lack of it's adapter socket shielding.
-Kent
Will scope soon..
Hi all,
Sorry for the delay...been very busy lately. Regarding the amps this original post is on, I still have not yet had time to scope them. But I will soon. They are still hands-down the best I've ever heard. I'm running them now through my Bohlender Grabener Planar Radia 420s. I've thusfar swapped into the same system my Mc30s, my Mc250, my old Mc754, my BGW 750b, my BGW 250c, a Denon POA 5000, a monster pair of Schulmacher Carillions, a pair of Dynaco MK-III's, a Dynaco ST-70, and probably a few others I have since forgotten. None has come close to these yet. I have also since built a new power supply. The 2 trannys in the original ps weren't quite matched well enough and I was getting a bit of hum and some nasty dc shift on my filters. Rather than play around with windings, I made a new ps with a giant Edcor I had laying around. It's even better than before. Right now I'm in the middle of building a Bob Latino Dynaco ST-120 just for kicks, to drive my Accoustats. I have my priorities. I'll post some results asap. All in all, I'd say with all the amps I've built (from scratch) and all I've owned, these are the only ones that I can honestly say that I will keep forever. If you're considering a build with the KT-120 I'd say go for it, you'll be pleasantly surprised.
Hi all,
Sorry for the delay...been very busy lately. Regarding the amps this original post is on, I still have not yet had time to scope them. But I will soon. They are still hands-down the best I've ever heard. I'm running them now through my Bohlender Grabener Planar Radia 420s. I've thusfar swapped into the same system my Mc30s, my Mc250, my old Mc754, my BGW 750b, my BGW 250c, a Denon POA 5000, a monster pair of Schulmacher Carillions, a pair of Dynaco MK-III's, a Dynaco ST-70, and probably a few others I have since forgotten. None has come close to these yet. I have also since built a new power supply. The 2 trannys in the original ps weren't quite matched well enough and I was getting a bit of hum and some nasty dc shift on my filters. Rather than play around with windings, I made a new ps with a giant Edcor I had laying around. It's even better than before. Right now I'm in the middle of building a Bob Latino Dynaco ST-120 just for kicks, to drive my Accoustats. I have my priorities. I'll post some results asap. All in all, I'd say with all the amps I've built (from scratch) and all I've owned, these are the only ones that I can honestly say that I will keep forever. If you're considering a build with the KT-120 I'd say go for it, you'll be pleasantly surprised.
The modern EH KT90 has a distortion signature closer to a GE KT88 and in some circuits can better the original KT88 even though a higher power tube.
The JJ KT88 screen as a tendancy towards Ei KT90 performer but not quite. In UL circuits, the value of the screen resistor can make a marked thd difference.
The issue I see with the KT120 is the top end drive performance as the input capacitances are higher than for smaller tubes. It will have a indefinite life at lower B+ voltages; but does this justify the cost for installing them ?
richy
I also came across this when I was running 6550's TungSol new edit in a quitar amp, fairly hard, 37W plate dissip in UL and suddenly backed up the grid bias into cutoff.....well I was disappointed, remiscent of a thermal runaway property, took a long time for the anode + screen currents to stabilise. Then I came across a tube that had been used +500 hrs over the others and getters showing dull grey and it ran away with the same test. It was at this stage I hulled the whole batch out. 2000 hr life exp that's it... not much more. It was after this I started fitting fuses in the o/p tranny centre tap.
KT120's the same trend ? sad short life given the time and trouble with assembly, precious materials etc.
richy
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Hi Richy,
Yes, I think the cost is justified! I have had no problems with them at all.
I am running the plates a little cool. I forget what now...I'll check that too when I get around to testing. They've got a few hundred hours on them now and look new.
These were originally built for kt-88. I added some extra switched cathode resistors so I can run 88's or 120's. No problems with the 88's either. The main reason I went to the 120's was for added power. I'm running them single-ended so am limited.
There's been no run-away, nothing getting hot, and no capacitance issues that my ear can tell. Actually, it takes them a good 10 minutes before they really start to open up. They have some of the best top end I've ever heard. They sing. I'll p-spice the schematic too or at least sketch it when I get back into them.
Best, Bill
Yes, I think the cost is justified!
I have had no problems with them at all.I am running the plates a little cool. I forget what now...I'll check that too when I get around to testing. They've got a few hundred hours on them now and look new.
These were originally built for kt-88. I added some extra switched cathode resistors so I can run 88's or 120's. No problems with the 88's either. The main reason I went to the 120's was for added power. I'm running them single-ended so am limited.
There's been no run-away, nothing getting hot, and no capacitance issues that my ear can tell. Actually, it takes them a good 10 minutes before they really start to open up. They have some of the best top end I've ever heard. They sing. I'll p-spice the schematic too or at least sketch it when I get back into them.
Best, Bill
I have the same observation. I am running a pair in a PP AB2 UL configuration with 200W clean output. It really takes some minutes until you get the full power.
Hans- Georg
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Hi, I'm running a couple of pairs in a Yaqin MC100B. They sound far more open with great bottom end compared to the various KT-88s i had tried. Lets see how long they last. Was only getting 200hrs or so out of the Chinese and Russian generics. I'm running them in triode mode with 440V @ 75mA. They start sounding good after 10mins or so. I've also fitted a time delay HT on relay to give the heaters a chance to get going. Wondering if to give them a go in UL.
I've had them running for an hour now and the bottom end is phenomenal, its tighter and has more extension. Going to fit hashimoto outputs in the new year.
Aleks1
I've had them running for an hour now and the bottom end is phenomenal, its tighter and has more extension. Going to fit hashimoto outputs in the new year.
Aleks1
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