• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Anyone out there with a KT150?

wfmali

Member
2003-05-09 8:15 pm
Hello, I am running SE-monos with [email protected] anode dissipation. What I do see is a dull red glow of the anode in the pin 1 area, the attached picture shows it quite nicely. I do own 4 KT150s, they all show the same behaviour, in both amps. KT120s with the same dissipation settings, however, do not show any signs of anode glow. Did anybody owning KT150s notice a similar behaviour? Would not really like to challenge mine with the rated anode dissipation of 70W.... Thought I bought them from a reliable source, do who knows :eek: ? Or this is a KT150 feature, not a failure - they accumulated at least ~150h so far quite happily... Any hint is very much appreciated!

Marcus
 

Attachments

  • kt150@50w.jpg
    [email protected]
    249.8 KB · Views: 815
Hello Marcus,

I built a KT150 PP-Amp during winter 2014/15, which has obtained in the meantime its 2nd set of power tubes - the first set had about 4000 hrs. The tubes are running with up to 600V plate voltage at about 80 - 85 mA current, measured at the cathode, so dissipation is also in the 50W-area.

I never observed "red cheeks" at this point - but yours appears to me also quite faint... But I must say, that I wasn't very satisfied with the quality of these tubes - with continuing age they started to get more and more unstable (running away to heavy red plating from time to time, but after switching off and cooling down they were ok again for quite a long time...), although grid resistance is 22 kOhms - far away from the 47 kOhms maximum. So I added an automatic working point control and regulation to keep them in safe conditions. Since then I had no more problems.

Also, the Getters were quickly fading, and with continuing fading, the instabilities increased. Seems as if the metal parts were not sufficiently degassed during production.

This is in a strong contrast to an amp with the 211-triodes (Psvane 211 MK II) I built last winter - these tubes have also in the meantime a lot of hours (> 2000) and are still looking like new...

The new set of KT150s appears to me as of a better quality. They haven't so many hours so far, but the fading of the Getters seems to be slower than in the former set - maybe their production quality increased with time?

all the best

Uli
 

Attachments

  • P1170254.jpg
    P1170254.jpg
    98.8 KB · Views: 753

wfmali

Member
2003-05-09 8:15 pm
yep, time of detailed information is long gone...
@Uli: nice assemble for some serious power. Do you phase-split using the input-transformer? Like that a lot...
I use my 150s with a CCS, and after some serious warm up time it is dead quite and stable. Getters are fine as well...just don't like that for my KTs 50W is about it, it is like running the final at 100%, which was never the intention...
Marcus
 
Chinese valves, don't you just love them.

Yupp ,especially their suppository-like appearance *bigfatgrin*!

From a commercial tube that is not dedicated for transmitting services I do not expect any glow on it's plate, unless the dissipation rating given in the datasheets are exceeded. Otherwise I'd say the tube itself, or the datasheet, are fake.

Over several thousands of years, longer than any other nation, the Chinese have gathered great experience and knowledge in making fire crackers. Obviously they continue to apply those in making tubes.

Best regards!
 
yep, time of detailed information is long gone...
@Uli: nice assemble for some serious power. Do you phase-split using the input-transformer? Like that a lot...
I use my 150s with a CCS, and after some serious warm up time it is dead quite and stable. Getters are fine as well...just don't like that for my KTs 50W is about it, it is like running the final at 100%, which was never the intention...
Marcus

Hi Marcus,

yes, this amp is a real "steam-engine" with an enormous power. I use the input transformer (Sowter) also for phase splitting. Expensive, but for avoiding ground loops indispensable. Input stage and driver are a PCL84, the video driver of old-time black & white TV-sets...

In general, I often have observed in these quite high-mu beam-power tetrodes an uneven density of the electron beams on both sides - often, the beam on one side is much stronger than on the other, so that most of the dissipation is generated at one side. So this side gets much hotter than the opposite side, which quickly leads to one-sided red plating even if the maximum permissible overall current is far from being reached. I think this comes from a not 100% even alignment of the grids in the tube - also a quality issue...

all the best
Uli
 
Over dissipation with these valves will heat the anodes up too far and you will lose power output. Increase the negative bias on the grid to just before the anode glows. That may make them last a bit longer.
Chinese valves, don't you just love them.

Aren't the "KT" tubes made in Russia? My KT120's all have Made in Russia printed on the base.
 
Hi, To add to the fury.... A licensee in the UK of some of our company's designs has reported the same thing. The tubes are used in push-pull with a CCS and are well within spec. Red anode stripes and glow are being reported on KT120 and defective tubes (new) right out of the box for KT150. This does not inspire confidence. Our company had initial issues with the distributor elsewhere mentioned but apparently that has been resolved after we kept send tubes back.
 
Hi All,
Yes, as Bruce says I had four KT120s that showed red at 60 watts total dissipation right out the box. I then returned these and swapped them for 8 x KT150s and of these:

-4 work with no red showing but of these two have quite deformed glass bulbs
-4 were defective. 2 of these showed red, while of the other pair, one made loud cracking noises out the box and both valves in that pair could not be balanced for dissipation.

So quality is a serious issue with these Russian tubes. I have had similar problems with Electro Harmonix and Sovtek output tubes too. Strangely enough I have had no problem with their small signal tubes.

I will continue to get these tubes from a sympathetic dealer who replaces them and credits return postage if there's any problem until I get satisfactory tubes.
David
 

wfmali

Member
2003-05-09 8:15 pm
Hi all,
seems that indeed the manufacturing quality is not entirely stable. Would also guess that missalignment might be the issue. If I change my KT150s for KT120s with the exact same settings (460V/110mA) there is no indication of any red plating..might be unlucky with my 150s, but lucky with my 120s :)
Marcus
 
All these KT tubes are commercial tubes,
no commitment to reliability or long life ((

I fear to use these tubes, they looks real fragile,
glass is thin, metal plate is thin, the whole tube
weight almost nothing, only price is heavy.

This is evidenced by the net weight of these tubes:
KT120 = 120 grams
KT150 = 130 grams

Otherwise Russian military tubes weight more:
6C33 = 200 grams
GM70 = 280 grams

http://www.thetubestore.com/lib/thetubestore/TS-KT120.pdf
http://www.tubeampdoctor.com/images/File/data sheet KT150 Tung-Sol.pdf
http://www.jogis-roehrenbude.de/Russian/6C33C/6C33C-B-6S33S-VExtendedDatasheetMB.pdf
https://frank.pocnet.net/sheets/084/g/GM70.pdf
 
Interesting. Sounds like the KT150 experiences are mainly down to compatibility. It's a shame one factory has a monopoly on production, so you wd think a EH KT150 cd be produced, seeing as its under the same parent brand. It wd certainly increase popularity for this tube.

Over the weekend I arranged audition's of what are probably KT88 SETs adjusted for 150's. I will listen midweek.. the amps are not high end parts but look pretty well made. One I believe is a TS Audio, the other is by a company called Mark Audio. There is also SAC Glowmaster, but their prices are beyond my budget.
What I really wanted was an amp tailor made for me, but being Thailand it looks like I now have to get mods done post purchase.
 
Last edited: