Looks like the KT-150s have come out to play

I see Parts Connexion in Canada has the Tung-Sol KT-150s for sale now.
http://www.partsconnexion.com/product25822.html
Price a mere $80/tube, 70 watts plate dissipation.
Haven't seen them anywhere else yet.
If someone wants to send me $640 I'll be happy to put an octet in my M-125s and let everyone know how they work

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The KT150 measures out at around 5½ inches tall and 2½ inches in diameter ... that's one mighty big christmas bulb!

For comparison, the KT120 tops out at just over 5 inches and 2 inches diameter ...

The KT88 is about 4½ inches tall.

So, following the progression, the KT 330 should be around a foot when it comes out ...  

sKiZo wrote:The KT150 measures out at around 5½ inches tall and 2½ inches in diameter ... that's one mighty big christmas bulb!

For comparison, the KT120 tops out at just over 5 inches and 2 inches diameter ...

The KT88 is about 4½ inches tall.

So, following the progression, the KT 330 should be around a foot when it comes out ...  

In which case the M-125 chassis will need to be the size of a ping-pong table and made from 1958 Buick fenders to accommodate the new xformers delivering 1 gigavolt of plate voltage -- which still won't drive the new generation of Maggies without clipping.

Thanx for the flashback ... I had a '57 Buick Roadmaster back in the day ... look in the rear view, and on a clear day, you could see almost all the way to the back bumper ...

To keep this post audio related ... that was the first year Buick had the FM Wonderbar ... and it had TUBES!

So, anyway ...

The salient point ...

Will these work with the ST amps? It like there's enough spare grunt to drive them properly ...

The power trannie might be a little feeble voltage wise.

The KT-150 would most likely need a different circuit/setup to sound best.   In an ST-120 you would need 100mA current per tube to BIAS a KT-150 at 70% max power.   The power supply can't supply that amount of current.  But two KT-150s in an M-125 amp might be worth a try.   Also a triode mode amp with KT-150s would be very interesting as well since plate dissipation is so high you might be able to get some decent power out of a pair.

Can't we just change the magic resistor (R39) to a negative value?

My question was whether the tubes would work at all. The KT120's can't be driven much past an extra 10% power, but they do work, and work well. And that's at 55ma bias. Bob drove his to 75ma and didn't see any extra power or sonic improvement, so they got backed down again.

sKiZo wrote:Can't we just change the magic resistor (R39) to a negative value?  

Perhaps a 9-volt battery? 

deepee99 wrote:I see Parts Connexion in Canada has the Tung-Sol KT-150s for sale now.
http://www.partsconnexion.com/product25822.html
Price a mere $80/tube, 70 watts plate dissipation.
Haven't seen them anywhere else yet.
If someone wants to send me $640 I'll be happy to put an octet in my M-125s and let everyone know how they work

They are now available in the USA at the tube store!!!
http://www.thetubestore.com/Tung-Sol-KT150

Hey Bob ... long as you're here ...

What happens if you try running mixed tubes for power ... Oh, say ... pairing a KT88 and a KT120 on a bank?



Reason I ask, seems like with a bias setting for each tube, they could be matched up to play well with each other. Maybe get the best of both ... or the worst. Or maybe something completely different ...

"What happens if you try running mixed tubes for power ... Oh, say ... pairing a KT88 and a KT120 on a bank?"

I don't think the amp will go into thermonuclear meltdown as the two different tubes will draw the same current if the bias is adjusted the same.  But you won't get a blend of sound of the two tube types as one tube of the pair amplifies the positive waveform and the other the negative side of the waveform.   For a given signal input if the tube pair gains aren't closely matched will result in more odd harmonic distortion.   Same with frequency response if the two tubes aren't closely matched will cause an increase in odd harmonic distortion.  It would be the same as one tube of a matched pair going south before the other.  But I can't see any reason not to try.  Guitar amps though may be best bet for getting a new and different sound with this idea so you better patent the idea!

Bob, if you're still there, have you ever tried the original TungSol 6550s, the ones that go for $300 a pop or so, in an ST or M-125? Are they worth the extra bucks?

Bob Latino wrote:
The VTA amps are all class A/AB1 which means that up to about 1/3 power they run in class A and then above about 1/3 power switch over to class AB1. When they are in class A both tubes are conducting all of the audio signal. When they switch to class AB1 each tube of the pair only amplifies 1/2 the audio signal. The actual point at which they switch over to AB1 is determined by the bias point. The higher the bias point the higher is the point at which the two tubes will switch over to AB1.

I sense concern with combining a KT88 and KT120 on a bank, but no OMG YOU"RE GONNA KILL IT! vibes, so it might be a tempting experiment once I get that meter issue out of the way and have a chance to break it in right.

Must ... resist ...  

One thing that popped out is your description of the A/AB1 switch point ... another advantage I hadn't really considered going with the larger KT120. I wouldn't be working the amp all that hard anyway, so if I'm pure "A" up to one third power, it'd only trigger a push/pull signal for instantaneous peaks? In that case, each tube in a bank would get to add it's sonic flavor without switching, and I'd think be able to blend better on the final output for that channel. I'm thinking that might just make for a killer jazz amp ... IF, of course, the combined sonics of the different tubes were worth the effort.

Then again, I have recent first hand experience in the distortion a compromised push/pull can create. So maybe not.

On a related note, any way to fudge the switch point from A to AB1? Smallish room with fairly efficient speakers, and a conservative listener could maybe benefit from that ... no switching, less hash?

Then again, what I was hearing out of the Psvane KT88's was absofreakin'lutely spectacular and in my mind would be hard to improve upon. Those KT120's, or any other tube or tube combination, got their work cut out for them to top that.

The BEST I have found are the modern production Gold Lion KT88's and Tung-Sol KT120.

Good to know ... I know you'd tried the KT120's, but that's high praise indeed ... and I just so happen to have a set ready to go!

Schiz, I would certainly echo, given my ~1 year's experience with M-125s, Bob's sentiments re: the reissue KT-88 Gold Lions and the Russian Tung-Sol KT-120s, although I've nothing else to compare them with. Both are very sweet and detailed and, knock on wood, no failures with either brand that can be blamed on the tube. I swap them out every three months or so just for a change of scenery, ditto the rectifiers. I did ruin one KT-88 when pulling it from its socket; hand slipped and I managed to separate the base from the glass. The ensuing curses exceeded any SPL that a tube amp can deliver. Jim McShane is your man for either of these tubes; he does a careful job of matching pairs and quads and a delight to deal with. Didn't even tease me too much when I fessed up about that two-part KT-88.

"On a related note, any way to fudge the switch point from A to AB1?"

You can adjust the point UP somewhat by raising the bias ... I have as a test run biased the Tung-Sol KT120's up to 75 milliamps per each tube (.750 VDC bias per tube) but do not recommend this. If you are going to experiment with higher bias points, my recommendation would be not to go above .650 VDC per output tube AND only if you use the Weber WZ68 solid state rectifier for these "experiments". If you use a modern GZ34 tube rectifier, the newer GZ34's will be operated above their design limits and will have a "shorter life span".

Bob

I have heard amps with a mixture of tubes. There is a Maggie dealer in the greater SF bay area that has mixed of tubes in push pull amps for years. But what I heard when I listen to the amps. was a lot of distortion. Pleasant distortion for the most part but still it was distortion. I have said for years that us audiofools love our distortion [most of it in the form of smearing and spreading the sound stage and causing a shimmering of the sound. I think that fact was not lost on David Hafler as I hear it in many of his designs. When we hear it we say wow I have never heard that detail in that recording before. The best example I can give to the sound would be: At the symphony does the music sound like you are setting in the first row and center or in the 30th row and center. If you like the 30th row better you love your distortion.

Bob Latino wrote:You can adjust the point UP somewhat by raising the bias ... I have as a test run biased the Tung-Sol KT120's up to 75 milliamps per each tube (.750 VDC bias per tube) but do not recommend this. If you are going to experiment with higher bias points, my recommendation would be not to go above .650 VDC per output tube AND only if you use the Weber WZ68 solid state rectifier for these "experiments". If you use a modern GZ34 tube rectifier, the newer GZ34's will be operated above their design limits and will have a "shorter life span".

I remember reading about your bias experiments on the KT120 when I was contemplating going with big bottles, and what I heard was there wasn't any sonic improvement raising the bias levels, but ... I also don't remember reading that there was any degradation. Still thinking if you could push the bias a bit to keep from triggering AB1, and find a happy medium between that and shortening tube life, some might find that to be a reasonable compromise ...

I was kinda sorta doing that when I first lit the amp due to the meter error issue. Come to find out, the bias was actually at around 70mA with a set of KT88's. Didn't hurt the tubes, and I assume not something I'd want to do for a prolonged period - but boy, was that thing singing! And I do know that Kevin been running his KT120's at 60mA for months with excellent results. I suppose that could also shorten tube life, but I'd also expect the impact to be minimal.

All in all ... food for thought. It's been said, distortion in a tube amp is the sonic equivalent of spice to a certain degree ... so, let's get ta cookin!

This is interesting ...



Licensed from TungSol or a Chinese version??

sKiZo wrote:This is interesting ...



Licensed from TungSol or a Chinese version??

Looks like an offshoot of Shuggies:
http://psvanetube.com/wordpress/

Wow!  Psvane KT-120s. Couldn't find them with the link above but try this one.  Introductory price of $189.00 for a quad.

Psvane KT-120