Matt The Cat
Prowlin' At 78 RPMs
WOW! Good to know. Guess I'll keep rolling KT88s and 6550s! No KT120s for me or my Mac amp.
Thanks for the advice.
-Matt
Thanks for the advice.
-Matt
New Tung-Sol KT120 output tube
- Thread starter Bob01605
- Start date
bricktop
Couch woofer
If you look at other power tubes, even the GE 6550A specified 50K grid leak for fixed bias. The original Genalex KT88 was spec'd at 100K+/- 20%. Technically, if an amp was designed to handle 6550s, the circuit should be OK for KT120s, as long as the PT can handle the extra filament current draw (probably not of major concern, only 19% more power from a winding that can most always handle it).
The MC275 also has an extremely low grid resistance since it's meant to drive grid current. The only issue there might be the extra filament current draw (1.9 amps vs 1.6 amps each).
The MC275 also has an extremely low grid resistance since it's meant to drive grid current. The only issue there might be the extra filament current draw (1.9 amps vs 1.6 amps each).
Bob01605
Member
Although a sales rep at New Sensor told me that the KT120's would be available in "early April", on their web site they now mention a "mid May" ETA for these tubes. I don't know what else to tell you ? Retail prices for these tubes will be $71.44 (singles) and $73.44 (each in matched quads). A pretty expensive tube ...
These tubes should work well in any amp that uses KT88 or 6550 output tubes and will probably last longer than either of the two. How they will sound ? When I get a quad I will try them out in my personal ST-120 and let you know.
Bob Latino
These tubes should work well in any amp that uses KT88 or 6550 output tubes and will probably last longer than either of the two. How they will sound ? When I get a quad I will try them out in my personal ST-120 and let you know.
Bob Latino
AudioGeek
too hip to function
Well, I already run KT-90/99's in my Baron (6 per side), which is OK after Mesa did the mod to allow for '88-types, and the transformers have plenty to handle them. Bias had to increase of course, but it upped power output from 150 to 225 wpc and I like the sound better than with EL34's.
Might call Mesa to ask about these new gizmos.
Might call Mesa to ask about these new gizmos.
Jim McShane
Well-Known Member
Yep, and I must say the published data is not promising. First off, as you've already suggested, this tube doesn't look like it'll drop into much. Indeed - look at the heater current requirements. 1.7 to 1.95 amps per tube! That's 6% to 22% above a KT-88. Four of those could end up needing as much as an amp (or slightly higher) more than a four KT-88s. How well that plays with anybody's power trafo is to be seen I guess.
The 50K grid circuit resistance is a big red flag to me. I agree with Wavebourn entirely.
As well, after looking at the curves I'm not sure if a lot of amps are going to produce the bias voltage required. Note that the curves are almost all with a screen voltage of 250 volts or less. With 450 on the plate and screen it's going to want to pass a ton of current.
Finally, if indeed the KT stands for kinkless tetrode somebody forgot to tell the designer. Those aren't my fantasy curves, to say the least.
I'll try to keep an open mind, but color me unimpressed by what's on paper anyway.
Bob01605
Member
Now some have said these KT120 tubes are basically "not usable" in any KT88 based amp. I agree completely that you will never get all the power and dynamics that these tubes ARE CAPABLE OF in a present KT88 based amp - BUT - I have found that in at least one instance they can be used in a KT88 based amp. No - you won't get 120 WPC out of these tubes in this amp but they seem to bias up nicely and sound good. YMMV and they may not work as well in other KT88 based amps. Below are some notes from a post of mine on the Dynaco Tube Audio Forum about the use of the KT120's in this KT88 based amp ...
Bob
"At about 5 PM on 4/15/10 the Big Brown Truck dropped off a matched quad of the new Tung-Sol KT120 tubes. I pulled the Genalex Gold Lion KT88's out of my personal ST-120 and dropped the four KT120's in there. They biased up fine with no issues. The bias system on the ST-120 is set up for KT88's. These tubes biased pretty much in the same general area that the Gold Lion KT-88's did. According to the KT120 spec they draw about 1.7 to 1.9 amps heater current per tube. The two 6.3 volt AC lines on the ST-120 are rated at 5 amps each. I let the amp warm up for 15 minutes without playing any music and then set the bias at 55 milliamps per tube. Later the bias was turned up to 65 milliamps per tube and then later to 75 milliamps per tube. IMHO these tubes sounded better as the bias went up. Most of the listening was done at 75 milliamps per tube. The rectifier was a WZ68 Weber Copper Cap and the three 12AT7 driver tubes were a Telefunken 12AT7 in the center position and two Mullard CV4024's in the two outboard postions. Although the ST-120 may be used in either triode or pentode mode, all listening with both sets of tubes was done in the pentode mode.
I listened for about 5 hours with various selections of acoustic jazz, vocals and some classic rock. This system consists of an OPPO BDP-83 Special Edition CD/SACD player, a BAT VK3i preamp, the Dynaco ST-120 power amp into a pair of Tyler Acoustics Linbrook II speakers.
Listening impressions ...
1. In general, the Tung-Sol KT120's seem to have a more "tubey" sound in this amp than the Genalex Gold Lion KT88 tubes that were in there.
2. The Genalex Gold Lion's have just a little more top end "air" than the Tung-Sol's..
3. The Tung-Sol's seem to have a more "full" sound with more mid-bass content than the Genalex tubes.
4. Both tubes seemed pretty much equal in soundstaging in both width and depth.
Other impressions ....
These tubes appear to work fine in the ST-120. At no time did the fuse blow or at no time were there any playing abnormalities. The transformers did not appear to get any hotter than when using KT88's in there but I honestly did not make any definitive measurements to verify that impression. With a retail price of over $70 each they are expensive but the Gold Lion's are $50 each so they are not cheap either. It is probably not fair to compare brand new tubes (KT120) with tubes that are well broken in (Gold Lion KT88's). These tubes will need more time on them and my impressions could change once they are broken in. I will probably give an update on the Tung-Sol's once these tubes have more time on them.
Bob"
Kegger
R.I.P. 1/12/1966 - 6/1/2017
Bob Question for you..
"Although the ST-120 may be used in either triode or pentode mode, all listening with both sets of tubes was done in the pentode mode."
You mean Triode or Ultra Linear don't you, I thought you ran output transformers with
UL taps, so I thought your switches were for Triode or UL, but not actual "Pentode"..?
"Although the ST-120 may be used in either triode or pentode mode, all listening with both sets of tubes was done in the pentode mode."
You mean Triode or Ultra Linear don't you, I thought you ran output transformers with
UL taps, so I thought your switches were for Triode or UL, but not actual "Pentode"..?
Bob01605
Member
Hi Kegger,
Yes - you are quite correct "ultralinear" - not actual pentode but I guessed that everyone calls them "triode/pentode" switches when in reality they are ultralinear/triode switches. All listening was done in the ultralinear mode.
Bob
Kegger
R.I.P. 1/12/1966 - 6/1/2017
Thanks Bob, I just like to keep things clear in my head.. 
(an push pull pentode here without regulated screens, is well..)
P.S. You take some killer pictures, that is one of the most clear eye
popping pictures I have seen in a long time posted by someone..:thmbsp:
(an push pull pentode here without regulated screens, is well..)
P.S. You take some killer pictures, that is one of the most clear eye
popping pictures I have seen in a long time posted by someone..:thmbsp:
Bob01605
Member
Thanks Bob, I just like to keep things clear in my head..
(an push pull pentode here without regulated screens, is well..)
P.S. You take some killer pictures, that is one of the most clear eye
popping pictures I have seen in a long time posted by someone..:thmbsp:
Hi Kegger,
Thanks for the comments on the photo ... This is a little off subject I know - BUT - About a year and a half ago (about Sept. 2008), I scraped up enough money (after paying my Ex her due - lol) to buy a Nikon D90 digital camera and lens package. The quality of the photos that I took went up immediately with this new digital camera. This camera has a couple of nice features.
1. It has an anti-shake mechanism in the lens that allows you to take sharp photos even at slow shutter speeds. I guess it somehow counteracts the slight movement of your hands as you hold the camera.
2. It has something called "D-lighting" that (somehow) gives extra exposure to the shadow areas without affecting the lighter areas of the photo. There are still shadows in the photos but now they have a little detail in them. A good example is that on the front of the power transformer in the photo - it's not all black and you can still see some detail of the plates that run horizontally.
I am no digital camera expert but the D90 just takes better digital photos than anything I have used in the past. I guess technology advances are helpful to all of us.
Bob
Jim McShane
Well-Known Member
Hi Bob!
You have a tremendous advantage over the typical user - not just because you have the skills and knowledge base to deal with tube electronics, but also because you KNOW your amp can handle the extra heater current draw these tubes could be presenting.
Plug these in a vintage (or modern, for that matter) amp that has barely adequate current capability for the stock KT-88/6550s and the extra current draw could kill a trafo. That would be especially true if a person happened to get 3-4 tubes at the high end of the KT-120 heater current spec.
Your amp has fixed/adjustable bias with sufficient range to accommodate the KT120. Some fixed bias (or completely non-adjustable bias) amps have insufficient range - and some cathode bias amps may need resistor changes to use the KT120.
I hope everyone reads what you wrote carefully - you said:
I would say it's unwise for others to make your statement into a generalization. I believe you'd agree.
Thanks for the great pic and the post! :yes:
Last edited:
Im glad I saw this thread again.
Im not exactly sure but Im willing to bet my Kt88 mono's will take them and Ive been thinking hard about checking it out. Except buying 12 of them will have to wait for a windfall. Or sell off some other tubes I dont need right now.
:scratch2:
Then again....How much power do I need
They will adjust from a EL34 thru a 6550 and under all circumstances have the PT & OPT's to handle it. I suspect they are Vintage Altecs but I dont know.
Unfortunately its a process to pull one out of its home for a checkout and the trannie types & values are "confidential" so I dont have any hard facts on them. They didnt come with a schematic and one isnt available, or at least wasnt when I got them.
I'll need to call the maker and ask a few questions.
BC I know you are lurking. How about it?
(Note to self - call Tomorrow)
..
Im not exactly sure but Im willing to bet my Kt88 mono's will take them and Ive been thinking hard about checking it out. Except buying 12 of them will have to wait for a windfall. Or sell off some other tubes I dont need right now.
:scratch2:
Then again....How much power do I need
They will adjust from a EL34 thru a 6550 and under all circumstances have the PT & OPT's to handle it. I suspect they are Vintage Altecs but I dont know.
Unfortunately its a process to pull one out of its home for a checkout and the trannie types & values are "confidential" so I dont have any hard facts on them. They didnt come with a schematic and one isnt available, or at least wasnt when I got them.
I'll need to call the maker and ask a few questions.
BC I know you are lurking. How about it?
(Note to self - call Tomorrow)
..
Just in from Parts Connexion. They're selling these for $90 a pair. I wonder how Bob's tubes are doing.
http://www.partsconnexion.com/product18880.html
http://www.partsconnexion.com/product18880.html
Bob01605
Member
Hi Isotonic,
It has been about a month since I put the KT-120's in the amp and I listen to them every day ... No problems and they sound good ... still, IMHO, a little more "tubey" sounding than the Genalex Gold Lion KT88's that they replaced. About 2 weeks ago I used a "laser thermometer" to read the temperature off various points on the amp. The amp had been on for about 3 1/2 hours and the ambient temperature, as I recall, was 69 degrees Fahrenheit in my workshop. The four KT120 tubes were biased at 75 milliamps each. The photo shows the temperature readings off various points on the amp. Sorry - I forgot to take a reading off the Weber WZ68 Copper cap ? The left side of any Dynaco ST-70 type amp will always be a little higher because the rectifier (either tube or a SS plug in like the Weber) will always give off a lot of left side heat. See photo below - all temperatures are in Fahrenheit ....
I intend to do another set of temperature reading with the Genalex Gold Lion KT88's in there but I just haven't gotten around to doing it yet ..
In regards to what Jim McShane said above "I would say it's unwise for others to make your statement into a generalization. I believe you'd agree." This is quite true. Anyone who uses these tubes in a KT88 based amp should do so with caution. I am making no generalization that these tubes may be used in any or all KT88 based tube amps.
Bob Latino
Rod Beauvex
Look at the tiny bunny...
So this is an entirely new tube design? No one ever made any kind of KT120 before?
According to Parts Connexion, this is a new tube based on the KT-88. There is a link on one of my posts. I believe it is a new design. It sounds like it will not work with all existing KT-88 amps, but might be a good choice for some of them. The price is attractive, and it is allways good to have another option. So as the owner of a couple of amps that will take KT-88's, I am most curious.
Kegger
R.I.P. 1/12/1966 - 6/1/2017
Yep that's my plan! :yes:
