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Why the KT120 & KT150?

MX117.MC7150

MX117.MC7150

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See a bevy of new amps using these tubes. My question is why? They make the same power as the predecessor amps from these manufacturers (CJ, ARC, etc.). The big downside (at least to me) is there are only one of two makers of the KT120 & KT150, so essentially no tube rolling. Is this just marketing BS or am I missing something?
 
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The KT120 & KT150 are more reliable tubes . For companies like ARC & CJ that is huge less warranty issues .
I had my VTL compacts upgraded to use 2 KT120 in place of the 4 EL34s for that reason
 
The 120 and 150 will take more abuse basically. In theory they can make more output power but only if the amp they are in takes advantage of those higher limits. I have a set of KT120 in an amp designed around a 6550 or KT88 simply because of their higher voltage ratings. Also, the KT120 quad was cheaper at the time I needed to buy the tubes, so that helped. I have since gotten a set of EH KT88 tubes, and I think the KT120 sounds better anyhow.
 
It's a way to sell more tubes, IMO. And it seems to be working. Think of it as another option as compared to a 6550 or KT88, rather than a whole new tube type with no tube rolling options. But caveat, the heater current is higher in a KT120, so it may not be a direct swap. Depends if the amp in question can handle the extra heater current demand from the KT120s

Concerning the sound, the KT120s might be the best sounding tube in that class on the market today. (Excluding the ultra expensive stuff which I have not tried). Gut punching bass, slightly rolled off highs, and a neutral midrange. The tube just sounds good from top to bottom. For a hifi amp, they are really quite excellent.

Electrically, the KT120s are not quite as linear as 6550s. But in a feedback push pull amp, that is hardly an issue with a decent amount of feedback. I measured performance of KT120's vs. Winged C 6550Cs in my CJ Premier 11 amp, and the two tube types performed quite closely. Same output power, but the Winged C's produced a bit less distortion at midband.

So what's not to like? Another tube rolling option for many of the 6550/KT88 amps that can dish out the extra filament current.

I have not tried the KT150's, so no comment there.
 
150’s are an expensive tube, something that effected my amp purchasing more than the ability to roll.

But 150’s sure are a pretty tube.
 
KT150s sound very good in my Inspire “Fire Bottle” SE Stereo Tube Amplifier HO, but I'm not crazy about their shape. I like the sound of the KT150 much better than KT88s (which sound too bright). My favorite sounding tube in this SEP amp is 6L6GC. IMO the best looking modern tube is the Tung-Sol 6L6G "large bottle" (6L6GC).
 
Can the KT-120 be used in a VTA ST-70. I'm currently using KT-88's and I really do not have any problems. But having yet another tube rolling option to play with is always fun.
 
airtime said:
Can the KT-120 be used in a VTA ST-70. I'm currently using KT-88's and I really do not have any problems. But having yet another tube rolling option to play with is always fun.
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I'd check with Bob & Co on the Dynaco forum on that - seems to me he only recommends the KT120's for the larger VTA amps. I may be wrong.

~ ~ ~

Way I hear it, the KT150's don't improve the smiles per mile much (if any) over the KT120's, but rumors are like (insert body orifice of your choice here) ... everybody's got one. Factor in double the price, and I don't much care how pretty the bottle is, ok.

Speaking of which - I love my KT120's. They run rings around any KT88 I've tried for bottom end definition. There again, a lot would depend on your musical tastes and what's important to you.

6sn7-installed.jpg


Oh. I also get a bonus approx 10w per channel using these. Not sure why, but it's there. I also expect they'll last forever as they're operating at nowhere near max rated power. These have probably got a couple thousand hours on them now and are going strong. Also super stable - can't remember the last time I had to change the bias settings.

ALERT >> DO be careful and make sure your iron can handle these bad boys. NOT something you'd want to try in an old Dynaco with factory iron fer instance. If in doubt, check the spec.
 
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I get the impression nobody is winding iron big enough to take advantage of the power these are rated for.
Also going big on iron introduces other issues.
(Really just spitting out what I've heard before)'
120s are insurance against high plate voltages.
Last time I looked nobody was making a 150w PP amp based on the150s
 
nj pheonix said:
I get the impression nobody is winding iron big enough to take advantage of the power these are rated for.
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Quite a few new amps that can push them properly, but ...

It's not only the iron that's an issue - an amp set up for a KT88 or smaller would need a whole lot of other tweaks to give you the full rated power of either of the TungSol KT series. I mention the iron, because the stock iron on the older rigs is usually working hard enough just to supply a KT88, let alone the smaller tubes they were actually designed for.

PS ... pretty sure that upgrading the capacitance reserve of an older amp is also a biggie ... I also upgraded my chokes - not sure that made any difference, but hey, I had the room with the custom chassis, so why not? <G>

(The little guy is what comes with the ST120 kit.)

compare-chokes.jpg
 
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Have tried KT120s in two amps. Really like how they sound, especially in the lower bass where they yield a strong, well-defined (for a tube) sound. One of my favorite tubes. Haven't yet listened to the KT150.
 
The newest amp I'm aware of that is being offered with the KT150s is ARC's new VT80SE. However, it is still only rated at 75wpc. Same as its predecessor.
 
nj pheonix said:
I get the impression nobody is winding iron big enough to take advantage of the power these are rated for.
Also going big on iron introduces other issues.
(Really just spitting out what I've heard before)'
120s are insurance against high plate voltages.
Last time I looked nobody was making a 150w PP amp based on the150s
Click to expand...
These YS Audio amps are not 150w but manage 100w per mono-block each using 2 x KT150's.
http://www.ys-audio.com/TR150power.htm

Using Hasimoto HW-100-5 OPT's
 
Those are in fact very nice. If they sound as good as their spec they would indeed be special.
The cost of admission is steep.
IIRC In the mighty Bogen thread, They were getting 100w (maybe a hair more out of a pair of kt 88s.
The 250w amp is using 3 matched pairs of KT 150s per channel.
 
Not bad for what they are.
The 100 watt mono's are 49000hkd that equates to 6274usd per pair.

Out of my bracket but there are many that have the income to not flinch at anything in that range and much, much higher. it's all relative to the individual i guess.
 
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Power supply current and volts are often a limit, but output transformer capability is no small part of it. Building transformers with both wide frequency capability and high power handling is pretty hard. I guess maybe thats part of the appeal of parallel output tubes. The winding ratios get lower, so less loss in the transformer.

But yeah, its very possible to get ~100 wpc from a pair of 6550 or KT88 tubes if set up right. I run a pair of KT120 to get the same power, but my amps don't measure appreciably different with a KT88.
 
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