KT90 opinions?

I'm thinking if getting a quad of EH KT90's as I've heard they have a bit livelier and aggressive sound than Gold Lion KT88's I'm currently running. My system has a pretty rich midrange as it is and the KT90's may be what I'm looking for. Anyone have experience or opinions on these tubes?

 

I have heard them quite a bit. I wouldn't buy a set now and I am not sure that they are even still in production. I can still get them but I don't bother. What you want is the KT120, which is a better tube than the KT88, especially the current production units. The Gold Lion KT88 is about as good as it gets now in that variety. The KT120 ups the performance level and the survival rate of the KT88 tube run at today's voltages. It sounds like a high performance KT88. The KT90 has a sound somewhere between an EL34 and a KT88 with voltage ratings about equal to a really good KT88. The failure of some examples has been spectacular however. I have yet to see a KT120 fail or have a set wear out in any amp that I have had or sold to a customer who has reported such anyway. Most amps are designed around the KT88 specs and with that, the KT120 is a great replacement that will stand-up to the punishment that some of the vintage amps would deliver. That will remain true until some idiot decides to push the envelope and design an amp that pushes the KT120 to it's limits.
-Bill

 

KT 120s are not the perfect tube, but for new production power tubes, I can live with them.

 

Unfortunately, my kt88 based amplifiers were not designed to take advantage of the kt120.
The extra current draw will put too much stress on the PT's.

I sure would like to give them a try.

 

I doubt that. The KT120 is a direct replacement for the KT88. It only draws about .1 to .2 milliamps more heater current, which should be well within the spec of any transformer employed in an amp intended for KT88 tubes. I'd talk to the designer of your amp or a tech at that company and see what they say. It would be highly unusual for any design to be that finicky. Now, you may not be able to realize much more output power depending upon the OT and the PT power supply but you should still benefit from greater headroom, wider bandwidth, and longer tube life.
-Bill

 

I may look into the KT120's. I hope my NOS Tung Sol 6550's keep going for a while as I like the way they sound. NOS tubes are getting so expensive that I may have to try some of the new tubes as an alternative.

 

Sorry, I meant to say that the KT120 only draws about .1 to .2 amps more heater current, not milliamps. That's a tenth of an amp, not a thousandths! Still, if there are four output tubes per chassis the total current increase on the heater circuit would be only about 1/2 amp. In a mono amp, with a pair of output tubes it's only 1/4 amp. Most circuits are going to have perhaps 25% more current ability than is drawn. It's still good to check if you can.
-Bill

 

Unfortunately per Mike Sanders of Quicksilver I cannot use the KT120's with my Mid Mono amps. I'm currently running Gold Lion KT88's and KT77's and while they have great clarity and imaging I'm looking for something with a little more aggressive top end and a little less fat in the midrange. Would the EH KT88's possibility qualify?

 

Hey KT88, I was going to switch to kt120's for longevity. jim mcshane said my citation and mcintosh amps
couldn't handle the extra draw.

I have thought about putting an adjunct filament transformer in one of the amplifier's circuits just to run the kt120's.
We'll see.

 

I'd be curious as to why. Did he explain it? It appears that those amps were designed originally for EL34 tubes. Maybe the OT just won't produce any more power when using a KT120 and he didn't recommend it for that reason. At only about another 1/4w draw on the filament winding, I'd think that they would work. Of course I haven't tried it in those amps and I must assume that he has.
-Bill

 

Maybe he just doesn't want to take responsibility for any failures, and I cannot blame him. Those amps are very old and probably should be treated rather conservatively at this point. I have been able to use the KT120 in all of the Rogue Audio amps which were designed for KT88 tubes without any trouble and with great results both sonically and in terms of reliability. I also retubed a pair of Cary monoblocks which were designed to run KT88 and was a bit concerned about those simply as I wasn't familiar with them other than they would flog a set of KT88 tubes in short order if biased to the original published spec. I biased them colder and after a talk with the tech there at Cary was advised to go ahead and use the KT120 as they did and to also bias the amps a bit colder even with those in place. I haven't heard of any issues from that customer.
-Bill

 

He said "The filament current draw is too high."

 

Well, there ya go. I would be looking at changing the 12AX7 tubes in the front end to get the change in sound you describe. It'll be more affordable anyway. What tube is in there now?
-Bill

 

EH 6922'S in the preamp and Gold Lion 12ax7 and 6922 in the power amps for driver and imput.

 

Get a couple of EH and a couple of Sovtek 12AX7 tubes and try those.They are not as good technically as the Gold Lion but they tend to be somewhat bright sounding by comparison to most other brands. That might take a bit of that midrange thickness down a notch. If it doesn't work, you are looking at either speakers or a tough choice with the amps.

I am not really familiar with your power amps, so it's hard for me to say that they are at fault here but if it is not the speakers, then it is the amps that I would look at harder. If it does come down to changing amps, there may be some weird capacitor choices in it that could benefit from a change to bring about a more neutral tone. That is a PITA if you can't do it yourself and is money wasted if it doesn't work, so it can be frustrating, and since I really don't know what's in there, my best bet is assuming that they are probably not the weakest link. After looking at your full system profile, I find that your speakers, although highly regarded at one time, are quite old and may not be able to reach the performance that they were once capable of. There are also a lot of really nice, new speaker designs that should be able to deliver a lot better performance using your present electronics package. Technology has marched along.
-Bill

 

Thanks for the advice, much appreciated.

 

No problem; I'm glad to help. I always start with the first amplifier tube when trying to change the tone of a rig. It has a global effect and is most affordable. The preamp is really the first place to look but you've already got EH in there and there really is not a brighter sounding tube IME.
-Bill

 

I had my CAT amps modified specifically for the KT120. The results are a definate improvement of an already great amp.