KT-120s... anyone using them?

[Chops]

I hope you'll bear with me on this as I'm not very knowledgeable on the electrical/electronics side of things. I blame my physics teacher for making it very dull, but that's another story.

The concensus seems to be a positive change in SQ when moving from KT88 to KT120 (looking forward to your impressions, Alex). What changes from a technical perspective? Greater output W? Increased damping factor?

My reason for asking is my EAR 890 uses KT90s (clues in the name, I guess ). Although there's still plenty of life left in them, KT120s could be an option on renewal (I'm assuming they're compatible). As Alex warns, I would check with TdP first, of course.

Chris

[John]

Please report back

[AlexM]

Bias stabilized after 10 mins, and has stayed bang on from then on. Currently
Running them at 40ma bias current, but may increase this later.

First impression is that the sound is clear and detailed through the mid and high frequencies, with very good instrumental seperation. It seems easy to hear into the mix to pick out individual lines, while still having good sense of the band playing together. Imaging is wide and deep, and nicely out of the box

Bass is less 'tubey' and resonant than with the genelex kt88, bass extension seems similar if not a bit better.

Only two hours on them so far, so just my first impressions. I expect them to improve through the burn in phase.

Regards,
Alex

[AlexM]

The sound is opening up nicely, and the mid and upper bass seems to be quite a lot more transparent. The texture of guitars seems more brightly lit, making the previous Genelex KT88s sound a little opaque by comparison. As before, stereo width, height and depth seems to have taken quite a step forward. The image is now less in between the speakers, and stereo production effects seem more noticable. I was listening to Yello Stella last night, and the panning helicopter seemed to be doing orbits around the listening room.

Interestingly the difference between SPDIF and Toslink outputs is now very noticeable, and I am actually prefering Toslink for the first time. Mids in particular seem more transparent, with instruments more distinct in the mix and low level detail to be easier to discern clearly.

Bass quality, if not weight, has improved quite a bit. Double bass from Brian Bromberg on 'Wood' is definately more clear and authentically wood-like. There seems to be less woof and muddle colouring the sound. At first it did sound a little less rich, but now I've adjusted to it and prefer this presentation. It is a little drier, but definately more accurate.

For £119 per quad I'm very pleased and this is definately the best the best sound I have heard from my Stereo 90.

Regards,
Alex

[Dominic Harper]

Dom is looking at getting some of these for his monoblocks, but as each monoblock takes 4 tubes each, we need 8 so not the cheapest. He will just have to keep saving for a while. It will be interesting to know your views on them after you have had them for sometime.

Natalie

[AlexM]

Dominic,

I don't think you will do better for £240 for eight power valves. Aahh just noticed you've posted as Nathalie - explains why this requires an indefinte period of saving

If you're using them in a circuit for KT-88s they should last a very long time also as they're just ticking over.

Alex

[Marco]

Natalie, when I get my spare set, I'll have eight in total and so will bring them round for Dom to try before he buys. Mine have also been cryo-treated

Alex, nice one, mate. It's a no-brainer, isn't it? What you're hearing is exactly what I heard in my own system, when comparing the 120s to 88s, which just sound small, weedy and a bit dull, in comparison.

Quite simply, if KT120s work properly in you amp(s), as seems to be the case with you, there's no going back! Enjoy

Marco.

[anthonyTD]

Hi all,
The KT120 is indeed a very good replacement for a lot of power amps using either KT88 or 6550, however, I must stress that it is not identical in electrical parameters i.e.; they will take a little more current from conventional AC heater supplies [average is around 100ma once valve has settled] which for high quality well made equipment, is not a problem, yes, you may find that the mains transformer will run a little warmer etc.

Also, the bias supply usually will need careful adjustment to exactly match the same steady state current as a KT88, however, with the KT120 having a considerably higher anode/plate dissipation of 60 watts compared to even the highest available KT88 [Svetlana winged c] of 42 watts it can be clearly seen that the KT120 when run as a direct replacement for KT88 and 6550 it will have seemingly a much easier life.
Bearing the potential higher power dissipation in mind, some amplifiers [mainly grid biased] can indeed be tweaked to produce even more power without getting anywhere near the maximum plate dissipation of the KT120.

however if you have a [conventional] cathode biased amplifier, care must be taken to make sure that the bias resistor values and wattage fitted for KT88 do not allow the KT120's to draw excessive current which could indeed lead to premature failure of the valve and equipment. On a positive note then, excellent results can be achieved using the new KT120 valve, but certain tests and precautions should be adhered to before doing the swap over, if your not sure then either consult your equipments manufacturer or a qualified technician for advice.

On a final note, the KT120 is a relatively new valve in terms of the regulars that have been around now for well over half a century i.e.; KT66, 6L6, EL34, KT88 etc, so,only time will tell if there are any serious negatives to using them, but from tests I have carried out in numerous equipment over the time I have been involved with this valve I can confirm that it favours positively with me, I just hope that its quality and relatively good longevity continues throughout its production as is often not the case.
Regards, Anthony, TD...

[Marco]

Yes, and as Anthony is too shy to say he has the Tung Sol KT120s in stock, and will be able to sell you a professionally tested (for shorts, etc) matched quad or pair. The valves he buys are all hand-selected from his supplier, and so after being tested, fully guaranteed!

So folks, if you would like some really nice KT120s, contact Anthony on: 01443 814738.

http://www.tubedistinctions.co.uk/main.htm



Marco.

[AlexM]

Anthony,

I have noticed that in my amp the bias current on one valve is hard to adjust down to 40ma (Rogue's recommendation). Maybe that pot is out of range, or maybe it is just some variation valve to valve. If I set them during the day, bias seems to drop in the evening. I assume the there must be some variation in the supply voltage, and getting them down to 42ma is the limit of adjustment on the trim pot for that valve.

What effect if any will running them at, say, 45-50ma have across the quad?. Does power rise with bias?.

Shame you're not a bit closer to me or I'd be intereste in you seeing what you could do with it to optimise around the KT 120 (oooh an some mods at the same time!).

Regards,
Alex