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So after years with KT150 I recently went back to the GL KT88 and must say I was very surprised with the outcome. My preamp is a Shindo Aurieges going into Quicksilver V4 mono blocks with 120 watts of output. Speakers are a very hard to drive Kef Reference 1 Meta, efficacy of 85 db with a 4 Ω (min. 3.2 Ω).The KT150s are what I would say in a word, base kings! Never realized a tube on its own could add so much base presence? Think of what a WE300b does to the midrange of its presentation. The degree of impressiveness is like to an equal of what the KT150 does to base presentation. Mind blowing!
As we all know prices of these tubes in general have gone up, especially the Russian stuff which now carries an embargo of 35% so I've been told by Mike Sanders over at Quicksilver. Who by the way has gone back to shipping out product with KT88s vs KT150s which are optimal for his newest transformers being currently used. All due to production limitations, costs and poor production out of Russia. Mike's tube screening methods are rigorous to which results in many rejections before he's confident in tube sound quality and longevity. Thus off the table till supply chain changes, prices adjust and Russia stops its EU aggression. So we wait till that day.
My current KT150s,(4 tubes per side, 8 in all), purchased from Mike at QuickSilver were sent to me Nov. of 2021. Prior to that when I purchased the amps new, they came with standard Chines KT88s in Nov. 2015 but I digress. Back to the KT150s, with regular use, these guys still hold rock sold bias but have started to diminish in the highs. 6 years on each set, damn Mike you know your tube grading, but at some point they start to give up their full sq potential.
So I bite the bullet and find a set of 8 platinum factory matched(whatever) Golden Lion KT88s through another dealer that promises burnin and matching within 5%(industry standard I'm told)?
Get them and install, bias set at a low but Quicksilver recommended 40ma for the duration of the breakin period. I can get to 55ma according to Mike as a max but will impact life expectancy. Anyway, what has surprised me during these few early days of breakin is how fricken base heavy driven the KT150s were. All good I think if you like base heavy emphasis on your music but for me it showed just how it takes over the entire audio presentation. Far from a neutral tube presentation and I think like most I lost sight of that when I first installed them KT150s, and was frankly wowed by the base explosiveness , I have tubes now that sound like solid state base. Great right? Well not really because now that I went back to the KT88, I've realized how well balanced this tube is and what I was gaining prior to the KT150 was a more balanced linear tube presentation. If it weren't for the limited availability and pricing I likely would have just retuned with the KT150 but as luck has it, I had to make adjustments that put me back into a place I started at a better place I think? Now I wait for breakin to complete but already happy with tone, dynamics and top to bottom presentation. Just my own cautionary tale of a tube guy becoming content with a status quo till forced to make changes. 💡
Thanks for reading! Comments?
d/s
.
Edits: 01/23/24Follow Ups:
The KT66 and KT88 are some of the world's worst IMD producers.
This is never ever quoted by amp makers.
The KT120-150 no suprise being Russian fat rubbish never had input from GEC-MOV and are a whole quantum leap worse with anode flex and electrode distortion thrown in.
If you like beam tetrodes you love odd harmonic THD and intolerable levels of IMD.
Maybe you do.
I hate that stuff.
Ok, thank you! ~d/s
"The (so called) advantages to the KT120 and KT150 are simple: they can dissipate more heat and have higher voltage ratings. - the tube curves of the KT 120 and KT 150 ARE NOT as linear as the KT 88."ie. as soon as you start pushing them a bit, the IMD turns the sound to mud and the THD especially 3rd and 5th harmonics go thru the roof.
If you want more clean power it's simple.
Bigger is not better. (ONLY reflector Saratov seems to think so/Mathews, cos they just want to sell that junk)Go parallel push pull or use TV sweep valves instead.
eg.
Any 6LW6/6LX6/6LR6 will wipe the floor with the KT 12/15/17 whatever, especially with screen drive, and you won't have arcing across an octal socket (because of TC)."A pair of 35LR6's will produce 250 watts at the onset of red plate into a 2500 ohm load on 650 volts.
4 of them made 504 watts into a 1250 ohm load on 650 volts."You will also find the sweep tubes are running perfect a decade after being abused for 1000s of hours, unlike this Russian QC nightmare rubbish.
Edits: 01/30/24
This is very interesting information. I'm not aware of these tubes you mentioned. I will contact the manufacturer, Quick Silver, to see if they will work with my V4 monos. I'm guessing they are not expensive? TY. ~d/s
They would have to change the entire design of their amps to do that.
The screen grids on sweep tubes are no higher +ve than 175-200V.
FYI both David Berning (EA-230) and Paravicini used sweep tubes often with screen grid drive.
They are a class act in linearity and longevity, something which any Chinese or Russian device won't even come close to.
FYI.
I have seen Quicksilver make glaring elementary errors in their amps which resulted in the immolation of large nunbers of the 8417 valves in those based units - totally unnecessarily it turns out.
I can only imagine they never read the original docs from Westinghouse or the tendency for large audio signal tubes to self bias and runaway.
The sweep tubes have HUGE cathodes which take lots of heater current.
They are capable of delivering over 1 amp as a result and lots of them still won't start glowing red until you start pushing anode diss to well over 80W-90W.
Just saying.
And the Berning designed Audionics BA150 was rated at 150 watts with similar tubes although that rating was with only 100 volts AC. The amp put out 225 watts at higher AC. I also know from a friend who was around David Berning at that time(he made David's first preamp) and he told me the BA150 prototype was turned on in 1072 and finally turned off in 1977 with no measurable wear on the EL-509 output tubes.
Another user of similar tubes(EL-519) was Melos who made monoblocks with 4 output tubes rated conservatively at 400 watts. And I should add the tubes(both Melos and David Berning) were screen drive resulting in output curves that were triode like.
The problem though with high output from these tubes is that the screen drive demanded high current drivers meaning you needed solid state drivers for maximum output. The EA230 was a second generation BA150 with a tube driver stage resulting in about half the output of the BA150 since a tube driver stage was limited in current drive.
"screen drive demanded high current drivers meaning you needed solid state drivers for maximum output."
nothing at all wrong with mosfets for driving grids at high voltage swings.
Here in front of me I have a pair of 1949 made AB2 amps. wiht originally 807 pairs in. I converted it to KT8 but seemed to make no difference to the sound.
The G1 drive which can push it to +18V positive comes from 6SN7 cathode follower.
Setting the bias properly for that is quite hard and the 6SN7 gets very hot.
If you have 300V aligned grids like in the 807 it's impossible to run screen drive.
The only reason why sweep tubes work, is because the tolerances and build quality are legendary, combined with a 1.5A-2A heater with monster cathodes to make relatively low impedance devices.
This makes the g1-g2 gain totally different and the curves far more linear.
There are also winding advantages with transformers with 1-2K anode loads + low voltages, like used in Geloso 100W amps and the hi gain EL520 range.
The KT66 and KT88 series have had their day,- that was in Reeves 100, 200W amps of the 1970s-80s.
They still work in Guitar amps as do the 6L6GC.
That's where they should continue to live and die, so who cares when they blow up!
Your comment about screen drive and transformers reminded me that the Melos 400 amp had a damping factor of 20 meaning it had very small interaction with speaker impedances that cause frequency response variations that almost all tube amps have. They never published a review but I saw Atkinson's graph of the Melos 400 frequency response with the simulated speaker load he uses in his tests and there was minimal variation from flat.
I had these many years ago. Nice amps, took up lots of room but looked beautiful and sounded like triode amps should. Only thing, a real pain in the ass was the screw driver needed to get the cage off. Sold them, miss them, wish I still had them even today.
Usual thing isn't it.
If you check you will find ALL valve amps measure FR and distortion at 1W into a resistive load (although you won't see it admitted).
I always measure mine at -2dB from maximum load with both sine and square wave into a genuine inductive/capacitive load (a speaker array) at all frequencies from 40hz-25khz..
(it's LOUD!).
One thing that immediately came across was the very astonishing difference in measured waveforms across the load depending on the amount of negative feedback.
That tells you that the obsession with damping factor is manifest rubbish.
It also tells you current drive (which has v high damping factor) can well resolve speaker driver reactions at medium to high frequencies - but of course NOT such stuff as ESL capacitive loads.
Driving into resistive loads (dummy 50W resistor mounted on a large heatsink), tells you sweet zilch,especially at 1W which is why this entire industry is full of fakery and BS.
A 5W amp running at 1W with a small transformer and cathode bias+loop NFB is a very different animal from a 100W amp running a large transformer at 1W..and mainly running CFB.
..never mind the very large differences in magnetic flux and reactivity on some of the older classics like UTC LS or Partridge compared with modern stuff with the much harsher sounding winding and core technologies.
It's why Partridge based British stuff, Citation, Scott or Fisher or certain Bogen have "that sound" which you can't do today.
FYI I use Scott OPT in my modern PPP amp, and they are fantastic.
Trancendar cloned them but they are gone now.
Both measurements and listeners agreed on them.
Clean v low IMD and v low THD.
Measure good - sound good.
ie.
Very far from the muffled distorting rubbish that's knocked out by people like Jadis for megabucks...
I know David. Use to own his TF-10AH along with the EA-2100. Wish I still had them. Back when I lived in Northern Virginia. At his home once for repairs, he at that time was running very old Magneplanar tympani 1-d screens. One of the nicest guys I've ever met. Along with Don Garber. A pity his passing.Thanks for the memory.
Edits: 01/31/24 01/31/24 01/31/24
I had a Zesto Bia 200 Select that ran four KT150s (two per channel) in class A. I lost three of the four in 200 hours or less; one for loss of vacuum and the other two with sparks and loud pop. The amp ended up being too hot for the AZ summers and I sold it with a new quad of KT150s. A costly experiment.
Open up your mind, in pours the trash. - Meat Puppets, 1987
Edits: 01/22/24
Just think if you had used KT170s! For the 150s to blow up, something wasn't right? Biasing or tube selection was off? Pity for such an expensive amp.
I was told a few years ago by the owner/designer of very good tube amps that the KT88 tubes were significantly more linear that the newer KT type tubes. Linearity is king when it comes to fidelity.
This is the case
and especially with the KT-90
it is a poster child for hysteresis!
incredibly noticeable....
Happy Listening
I think speakers have something to do with it as well as amp design.
Edits: 01/21/24 01/21/24
The advantages to the KT120 and KT150 are simple: they can dissipate more heat and have higher voltage ratings. Alan hits the nail on the head, the tube curves of the KT 120 and KT 150 ARE NOT as linear as the KT 88. IPSOSHITSO, they distort more.
Hi Gary. It's been decades but I recall some good fun at Murray Zeligman's.
Mike thought they were probably a good replacement on his V4? They were more expensive and did last longer but didn't sound as nice on my Kef reference 1 Meta, where as in my previous speakers, the Eminent Technology LFT8B, the pronounced base was a welcome addition for the ET speakers.Goes to show you, never knew till you time them at home on your own gear and at home.
Edits: 01/21/24 01/21/24 01/21/24 01/21/24
It ends up being an issue of OPT matching to the Output tubes - and when you want the flexibility of disparate tubes...
Happy Listening
i can not confirm your impression. my lyric Ti 140 can handle KT150 and i tried them critically again and again but never was satisfied with their bass performance which was lacking and sluggish to my ears.
may be your amp has a more sophisticated circuit supporting KT150 perfectly.
Bias not only affects power-tube performance, but it can also impact the sound and the lifespan of said tubes. As already mentioned, if the bias voltage isn't negative enough, then the tubes will run hot. This is sometimes referred to as "biased hot," "red plating," or "running hot," and it not only significantly shortens tube life but can also result in a lack of output power and punch. On the other side of the coin, if the bias voltage is too negative (a.k.a. "biased cold" or "running cold") the amp will sound dull and lifeless, and some unwanted and unpleasant-sounding crossover distortion could well occur — and, much as we guitarists love distortion, this type sucks!
So, just like the idle on a car, the correct bias-voltage setting on your amp is imperative for performance, tone, and tube life. Thanks for playing your wisdom and way with words forward,
Very nice integrated amp, made in Germany. What speakers are you running? What output tubes have you gone to, KT88 or maybe TS KT170 used in the Ti 100 MKII?
The QS V4s before being discontinued had a cycle refresh with upgraded transformers that were suitable for a wide range of output tubes, from the el34 to the kt150. So yes they had the correct voltage to handle and maximize the kt150 tube. Before the change he had like 300 screen v. Not enough to push the kt150s which do much better around 600 v.Very puzzling?
Edits: 01/19/24 01/19/24 01/19/24 01/19/24 01/19/24 01/19/24 01/19/24
You are incorrect in assuming the plate voltage on the V4s changed from 300vdc to 600vdc. The screen grids are at 300 vdc.
Yes, correction. Screen voltage.
Are the newest version still 300 screen v? Now disconnected.
Edits: 01/19/24
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