A little more information

The two main activities in my life: Helping the hungry in the late hours of the night and helping guitar players sound better one amp at a time.

I always try to remember that in order to do good one has to take action and actually do something.

I was born and raised in Los Angeles. I have watched the city and Southern California change for well over half a century.

I can be found on facebook at www.facebook.com/mylesr or on twitter at www.twitter.com/myles111us or on my own Guitar Amplifier Blueprinting website at www.mylesrose.com

Los Angeles Architectural History

Los Angeles Architectural History
1935 Art Deco at some of its finest: No. 168 - Griffith Observatory- (click on the photo for information)

Thursday, February 6, 2014

KT-150 Tung Sol vacuum tube

Test results and observations on this new tube offering.

Tube Depot ( great folks) says that a pair will produce 300 watts yet the max plate dissipation is spec'd at 70 watts.  I don't understand that 300 watt figure.  A KT88SV as a side note is 50 watts and a regular KT88 is 42 or so watts.  They run $90 per tube.  

I will be looking at these asking myself ... is there a reason?  How do they sound when driven to distortion?  (A KT88 distorts in a lovely way but a 6550 distorts in a quick and raspy way that is not too pleasant).  Do they last at voltages on the spec sheet?  Most tubes today do not.  How long will they keep going at full rated voltages?  (My standard series of life tests.)  What do their traces REALLY look like?  Design spec drawings are often not close to being accurate.

Click on "Read more" to continue

The heater current mentioned?  Not really an issue for any modern amp.  A KT88 is around 1.6amps and this KT150 is noted at 2.0amps maximum and 1.75amps minimum.  An EL34 is 1.5A as a sidenote.

https://d1sjrnpi226dnf.cloudfront.net/spree/attached_files/ts-kt150.pdf?1390421029 - the published design and performance specs.

For those that wish to compare so other power tube data sheets of some tubes these are intended to replace:

Here is the promotional stuff from my friends at Tube Depot:

With an internal plate length of 55mm and a massive plate dissipation of 70 watts (a KT88 is typically only 35mm and 42W), the Tung-Sol KT150 is the most powerful octal base beam tetrode ever produced. A pair of KT150's are capable of producing 300W of audio power. The thick glass envelope has a futuristic "egg" shape structure which improves thermal dissipation and provides the strength needed for a superior vacuum. The Tung-Sol KT150 is built to survive the most demanding audio environments possible.

The overall sound of the KT150 is thunderously powerful. The bass is tight, full, and precise with a neutral midrange and transparent high end clarity. The dynamics are unlike anything we have ever heard before. This is truly the tyrannosaurus rex of beam tetrodes.

Because each KT150 consumes 2.0A of filament current (more than the KT88 and 6550), we recommend contacting your equipment manufacturer to insure your power supply is capable of powering this tube. Additionally, this tube is 5-1/2" from bottom of base (not including pins) to the top of the glass. Insure you system has at least 6-1/2" of clearance from top of the tube socket to the overhead limit. There must be room allowed for both tube installation and cooling.

If your sound demands the most, this is the tube.


Voltage tests:  Testing a duet.  One of the tubes failed bringing up the voltage to maximum stated value at 612 plate volts.  At this point the bias was still set at -80v.  The tube was under NO load and producing no output.  In an amplifier even at idle this tube would have failed. Holding the plate voltage at 625 the remaining tube failed in less than ten minutes.  This was as the bias was being adjusted to a level to put the tube into an operational mode.  At the point of failure the plate dissipation / voltage indicated that the tube was producing 41 watts at the time it failed.  

The curves on this tube in no way indicate KT characteristics.  The tube performs very much like a 6550.  The distortion curves when pushed (at lower voltages adjusting the bias) are very close to those of a 6550 rather than a KT88.  Ultra Linear operation has no advantages for this tube which is not the case with a KT66 or KT88.

These tubes look as if a burn in would improve initial stability.

2/7/14 1530pst:

KT-150 update:

When I came back from lunch and pistol shooting (shotgun shooting this morning as a side note) the duet of KT-150 tubes were still running.  They have drifted and burn in is worthwhile... very worthwhile.  If you use these in any amp recheck bias after the first hour, at five hours as well.  I am still seeking stability.  Running out again but will up the wattage demand and continue testing.  There are now 10 hours of run time on the duet and three of those hours have been running at 50+ watts per duet, far below rated output but the first step in operational testing.

Date Time Average Peak
2014:02:07 09:11:07.71 49.44 51.27
2014:02:07 09:11:08.07 50.16 51.32
2014:02:07 09:11:08.11 49.02 51.32
2014:02:07 09:11:08.71 50.97 51.71
2014:02:07 09:11:09.31 50.09 52.96
2014:02:07 09:11:09.41 51.36 52.96
2014:02:07 09:11:09.51 49.31 52.96
2014:02:07 09:11:09.61 47.72 52.96
2014:02:07 09:11:09.71 60.03 60.04
2014:02:07 09:11:11.11 47.39 57.76
2014:02:07 09:11:14.89 46.76 57.76
2014:02:07 09:11:14.99 45.84 47.49
2014:02:07 09:11:15.09 45.36 48.68

Keep in mind this tube has a 70 watt max plate design spec.  Then again, an EL34 has a 25 watt max plate spec yet four of them in some amps produce 140 to 170 watts without issue.  The claim of 300 watts for a duet of these KT-150s is an interesting claim.  We will see.

Side note - I have seen over 120 watts produced reliably by a duet of KT88SV tubes often.

2/7/14 - Duet #3 still running.  No issues.  Raising the power.  575/550 plate and screen voltage.

2014:02:07 15:41:50.66 80.76
2014:02:07 15:41:50.76 80.76
2014:02:07 15:41:50.86 80.78
2014:02:07 15:41:50.96 80.78
2014:02:07 15:41:51.06 80.13
2014:02:07 15:41:51.16 80.26
2014:02:07 15:41:51.26 80.44
2014:02:07 15:41:51.36 80.44
2014:02:07 15:41:51.46 80.76
2014:02:07 15:41:51.56 80.87
2014:02:07 15:41:51.66 80.87
2014:02:07 15:41:51.76 80.87

80+ watts is the maximum design rating (70 plate + 9 screen watts).  I will run this duet for a long period or until one of the duet fail.

The last duet may be run at maximum voltages but may not be subjected to the maximum voltage claims for a few reasons.  Many components today other than tubes may not run at 800 volts.  I do not think too many designers would design an amp to run at 800 plate volts.  Tube prefer current to voltage, they just sound better.  High voltage amps can tend to sound harsh.  These high plate voltage design amps are also less reliable and tube life is shorter.  In essence, there is really little reason to run the voltages to extremes.  I may drop the voltage to 500/490 in a while and drop the bias voltage to keep the same general level of power output yet cycle the power output while capturing the waveforms on sample and hold gear.  Dan Boul of www.65amps.com has seen the sample/hold gear used in his shop for pickup balancing, a different story perhaps sometime, perhaps a short segment some day on a 'Lunch with Dan Boul' Ustream show?

Factors to consider on first tubes tested which failed:

These are large tubes and large tubes are less durable physically. They don't like to travel and do not do as well in transport or shipment.  Grid wires slip their posts and there are other things that can happen.  The KT66 sees these issues quite often, another large tube.  The tubes were pack as matched duets and the first duet may have been dropped while being packed for shipment perhaps.  The second duet currently under test are performing properly at this point.

Side note from one of the best amp techs and designers in the business, Blackie Pagano:

hey myles, for grins i knocked together a kt-150 SE in a client supplied fender chassis a month or so ago. biased it all the way up to rated dissipation and it was stable and made 20 watts at clipping! nice, classic SE waveform, clipping softly into 2nd harmonic distortion. sounded great and very ballsy but...became quite microphonic shortly. too microphonic for combo use...boo. i sent it back.

If you want to contact Blackie you can find him at:

Gioachino Pagano

2/9/14 Update

Date Time Average Peak
2014:02:09 08:58:28.80 41.58 46.04
2014:02:09 08:58:29.71 52.43 52.44
2014:02:09 08:58:30.11 49.61 52.44
2014:02:09 08:58:30.21 39.28 52.44
2014:02:09 08:58:30.31 41.11 52.44
2014:02:09 08:58:30.91 44.44 62.04
2014:02:09 08:58:32.31 91.68 91.69
2014:02:09 08:58:32.41 89.24 92.22
2014:02:09 08:58:33.11 86.09 89.51
2014:02:09 08:58:33.21 85.99 89.51
2014:02:09 08:58:34.41 83.76 89.96
2014:02:09 08:58:35.71 58.14 74.58
2014:02:09 08:58:36.71 42.33 74.58
2014:02:09 08:58:37.21 59.92 70.03
2014:02:09 08:58:38.61 59.13 79.46
2014:02:09 08:58:38.71 66.97 79.46
2014:02:09 08:58:38.81 53.34 79.46
2014:02:09 08:58:39.51 48.31 51.08
2014:02:09 08:58:39.61 48.76 51.08
2014:02:09 08:58:40.81 50.02 59.3
2014:02:09 08:58:42.41 77.96 85.09
2014:02:09 08:58:44.61 65.84 81.25
2014:02:09 08:58:48.81 38.59 69.59
2014:02:09 08:58:49.61 38.15 69.59
2014:02:09 08:58:49.71 39.13 39.13

The duet continues to run without incident.  At this point I assume that the tubes may fare as typical for current production tubes.  They will be more prone to physical damage than a typical 6550 or KT88.  I feel the mica support structure in inadequate for a tube with internals of this size and mass.  If you travel with this tube be careful.  Very careful. 

The tubes did reach stability after about 25 -30 hours.  The life tests indicate nothing particularly good or bad, perhaps about 1/3 life of a good NOS 6L6 which rates at about 6,000 hours in average tests.  BUT.... use varies due to many factors.  These tubes may die from physical damage long before they burn out.

Tone and sonic characteristics are personal taste and preference.  Feel free to leave comments below as to your own findings.

Bottom line from my own point of view?  A big tube that is physically fragile that has no particular power or voltage advantage over a current KT88.  I love the shape though, looks like the Russians worked a cool deal with IKEA to make the bottles for the tubes from the vendor that makes their chandelier light bulbs.  



  1. Hi Myles, It looks like this is going to be another dose of bad news for tubeoholics! I'm a bit surprised at Tube Depot as well. Who can you trust anymore? Is anybody making anything halfway decent now or are we all going to have to jump ship and fully embrace solid state? Gary

    1. The folks at Tube Depot are first rate folks. They are passing along what they are told by the makers or making assumptions based on the claims of the manufacturer. Nothing wrong there.

      They do test and match nicely across their sales line and I trust these folks. They do not run destructive tests as is the case with most other tube suppliers. I don't fault them for not doing destructive testing. Heck, it is pretty clear to me that even the folks that MAKE these tubes don't test very well. I wonder if the maker is even ISO 9000 compliant. I doubt it.

    2. Hi Myles, New Sensor is the manufacturer - that's Mike Matthews' ExpoPul factory in Russia, right? He "owns" most of the old, respected tube brand names. If you doubt they are ISO 9000 compliant that also follows for the rest of the stuff they churn out. Who's left? Shuguang and JJ - at least as far as guitar amp and usual hi-fi amp tubes are concerned. What's your opinion of those makers? I gotta say the future just looks worse and worse. Prices keep going up, quality keeps going down. I think the fat lady has started singing! Gary.

    3. Gary,

      Yes, this is another New Sensor tube.

      JJ is currently the most consistent but does have good and bad runs. Shuguang are the folks that will make "anything" for anybody who will pay them such as "custom" tubes. They made the GT exclusive tubes (JJ made two as a side note - KT88SV and E34Ls) such as the 12AX7M, 6L6GE, 6CA7GE, 6L6CHP and 5881 short bottle. Shuguang has a few strange business practices. An example is when they would sell GT parts which GT bought and sold to Shuguang for use in the 6L6GE (pins, bases, plates, etc) to folks like TAD who would then use the GT parts (illegally) in their version of the tube. Mike Matthews (Reflektor / New Sensor) had a contract with GT to produce the KT66HP (which was a spectacular tube) which was a GT exclusive tube only sold by GT. For some strange reason the inventory went out the back door to a German tube seller and then all the equipment to make the exclusive tube was either trashed or lost. Part of the issue with many of these companies are business practices. They are not what somebody my age would call honorable. RCA, GE, Raytheon, Sylvania .... companies that were always thought of as honorable. Today it is a matter of putting out a "new" tube with a purchased name and when sales drop off make a small change that does not make the tube any better but allows them to put a new name or spin on the tube.

    4. Gary,

      I will break this down and reply...

      Hi Myles, Thanks for the comments. I always enjoy "inside info" from people who have actually been involved in the industry. I understand that Shuguang has some sort of tie-up with Korea's LG Electronics. Would you know if this has anything to do with their audio tube production?

      ... I do not know the answer to your question.

      Regarding GT, did they actually have any production with JJ? I seem to recall that Pittman worked with Tesla on EL34 type tubes.

      Aspen Pittman had a long standing relationship with both Tesla and later JJ. GT worked closely with them to develop EL34 tubes which were exceptional (Tesla) and other tubes. In later years when Tesla was gone and JJ was in the picture the GT exclusive E34Ls was developed. This was not the same tube as the JJ E34L. The JJ was a 25 watt EL34 type. All EL34 tubes were 25 watt tubes except the GT E34Ls which was a 30 watt tube. It was a very stout tube with a very long life. The GT KT88SV was also a proprietary GT tube built under contract by JJ. These GT tubes were also sold by Penta Labs. The KT88SV was a 50 watt rated tube. Other KT88 tubes had a rating of 42 watts. These worked in spectacular fashion in Marshall Major amps and the Dr. Z KT88. Many folks loved them in audio gear.

      Finally, what usually causes modern tubes to fail?

      I have written about this in reams. If you read a bit more of my past tube info you will find a lot of info. Basically it is materials, contamination, lack of QA/QC, slipped grid wires, tolerances not consistent and no government or military reason to make a proper product ... oh .... and lack of competition in the market.

      I have had many ... MANY amp makers tell me that if they could buy a 12AX7 that worked like those of the past they would pay $75 or more for a single tube.

  2. Hi Myles, Thanks for the comments. I always enjoy "inside info" from people who have actually been involved in the industry. I understand that Shuguang has some sort of tie-up with Korea's LG Electronics. Would you know if this has anything to do with their audio tube production? Regarding GT, did they actually have any production with JJ? I seem to recall that Pittman worked with Tesla on EL34 type tubes. JJ acquired Tesla's equipment when they decided to exit the audio tube business. At least that's been my understanding for a long time. Finally, what usually causes modern tubes to fail? Back in the late 60s and 70s I would rarely see a dramatic failure. Tubes mostly became "weaker", some preamp tubes in guitar amps went microphonic and a few became noisy. I only ever saw one RCA 6L6GC red-plate and was more likely to blow a fuse than lose a power tube! I think I only had one rectifier, a 5AR4, that lost vacuum - getter flash turned white. Recently a brand new Ruby 6L6GC - for no obvious reason red plated and the flash went white. I don't know if it's substandard "ingredients" or bad manufacturing or what but new tubes are a real crap shoot. Thanks, Gary.

  3. Gary,

    Seems as if my reply ended up above your questions but there you go.

    1. Hi Myles, Thanks again for all the answers. Sorry if I seem to be bombarding you with questions but there aren't many truly knowledgeable tube guys out there - at least not many who seem inclined to give straight answers! One more, after seeing Blackie Pagano's KT-150 in the Fender chassis - do you have any opinion about modern power tubes mounted "upside down"? I always preferred upright mounting even back in the "old days" because I felt that the heat streaming into the base, pins, and socket was just an additional stress factor. Perhaps the old tubes could handle it but I wonder if anybody has experience of unusual failures in modern tubes or if they even test tubes upside down? Thanks again Myles! Gary.

  4. Gary,

    The tubes we commonly see in guitar amps are designed to work in any mounting plane. This is specified in the design spec. In the past, the STR387 made by Sylvania for Fender had a specific design request (Special Tube Request) from Fender which told Sylvania that the tube would generally be mounted hanging down from a chassis and in close proximity to a loudspeaker.

  5. Hi Myles, Yes, I agree about the Sylvania STR387 as well as many "non-STR" tubes of days gone by. While my preference was always for upright mounting even back in the 70s, my real concern is for modern tubes (and sockets - particularly those mounted on PCBs). I have a suspicion that they are better off upright than upside down and just wondered if you had any opinion. Thanks, Gary.

    1. Gary,

      I don't have a preference as long as the tube sockets are good quality such as Belton or have some secure way of keeping the tube in the base during vibration or travel.

    2. Hi Myles, I just wondered if you've done any relatively recent testing of other current production power tubes? I see a lot of data on preamp tubes but it would be interesting to know how JJ / New Sensor / Etc are doing with their EL84, 6L6, EL34 and so on. If you have been doing these tests and posting the results elsewhere would you kindly point me to them? Thanks again, Gary

    3. I do a lot of ongoing output tubes tests but other than reliability the sonic character of preamp tubes makes much more of a difference on how an amp feels and sounds in most cases.

      Output tubes are more expensive to buy in large enough quantities for a somewhat accurate test as well so this is also a reason preamp tubes are tested more often than output tubes. On my GAB website there are a number of pieces written on output tubes as a side note.

      Bottom line on current production power tubes for the most part: Less reliable than ever, more inconsistent than ever, lower output on average than ever and shortest life than ever. Bottom, bottom line .... Quality continues to decline as names change that are printed on the bottle as cost rises.

  6. The story on the KT66HP is quite interesting. I used some of those a few years ago in several Marshall amps and I felt that they were really good. Then new ones were no longer available, damn! New Sensor offers a KT66 in their "Genelex" line as current production how much do they have in common with the KT66HP?

    1. The old GT HP was terrific. New Sensor may or may not have been the folks who stole the GT tooling which shut down production of the GT version. If they are the folks that stole the tooling you might just see some design similarity. ;)

      The again, New Sensor (Reflektor) QA / QC is abysmal so it might be a case of a copy of a BMW made by the old Yugo car factory. May look the same but ....

    2. Thanks for the info.... I wonder what's going on with New Sensor; it seems like maybe 20 years ago that the Sovtek tubes even if they didn't sound great were quite reliable. I'm thinking of the wafer base 5881 and their 12AX7WA,WB etc.

    3. You mentioned the ones that are still the most reliable of their lineup. They continue to go downhill. As they buy more of the famous names to put on substandard offerings the quality continues to decline.