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PostPosted: 12 Apr 2017, 20:47 
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Hi, Well, three out of 4 is better. It was nice to think the problem was at an end. :bawling: Still they should be easily able to handle 50W. I would expect 60 to not be a chore either for a KT150. The standard dissipation in the kit amps for KT120s is 52 watts (combined screen and anode). My test pair here (for tube longevity and such) are at 56 watts.

Good listening
Bruce

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PostPosted: 13 Apr 2017, 12:37 
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Juancho wrote:
:eek: :eek: :eek: One redplates badly........the others not at all at 123ma dissipation (approx 50 watts)


OK.
One last suggestion before I retire from this discussion. It will involve removal of the OPT, and you will need 25 & 50-watt lamps at the appropriate voltage for your location.

Connect the *PRIMARY* of the OPT to mains voltage with the 25-watt lamp in series. This should be putting about 1/10 A on the primary at 240 VAC. Not a lot of current. And less, surely, than actual B+ and amperage in operation.

Monitor the temperature of the OPT and if there are any changes in secondary voltages.
Monitor the actual current on the primary. If this remains constant for an hour, install the 50-watt lamp. You could take this to whatever level you think is safe for the OPT - as in within its rated current/voltage parameters.

The idea is to discover if there are any temperature/current related faults.

Assuming (dangerous) that you have established that 100% of the passive components in all the problem children are good both on the bench and at full operating temperature.

I keep a heat-gun ( http://i.ebayimg.com/00/s/NTAwWDUwMA==/ ... G?set_id=2 ) to look for hot-spots. They are quite useful.


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PostPosted: 15 Apr 2017, 03:27 
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Joined: 25 May 2016, 16:30
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Yet well I ken the circuits where tubes glow,
Have traced the fount whence streams of electrons flow.
Glow, O ye tubes! Glow for whom ye may,
For me ye glow not! Merrily,redplating away

So for the latest batch after early promise three tubes glow very significantly. As always, adjacent to Pins 1 or 4


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PostPosted: 15 Apr 2017, 08:10 
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Joined: 06 Jun 2008, 18:23
Posts: 4918
Location: Australia
Fight ye not the red devil
Yet his strength in numbers grow
Find the heart of the devil himself
To stop his evil glow.

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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
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PostPosted: 15 Apr 2017, 15:16 
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Forsooth, What specters of gloom and doom hath I created? :king: I may henceforth have to give up on the incandescent devices and start playing in the sand. :bawling:

Good listening
Bruce

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PostPosted: 15 Apr 2017, 17:46 
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Location: Chilliwack, BC
King of the Glass, as it came to pass,
Thought his heart may glow no longer,
But his skills he sought to make stronger,
To study and learn, iron at the ready,
To control the sand like Paul Atreides

(gawd, only in geekdom can we start with a "mayday" and end in really bad poetry :D )

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* Ratings are for transistors - tubes have guidelines*
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PostPosted: 16 Apr 2017, 04:50 
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[quote=
(gawd, only in geekdom can we start with a "mayday" and end in really bad poetry :D )[/quote]

A pleasant diversion! I'll report back when I've completed the next build in a few weeks.


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PostPosted: 17 Apr 2017, 13:03 
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So I've had 20 KT150s and 4 120s. Of these:
-four are good at 122ma or 51 watts. Any redness is at the absolute margin of visibility
-four more were similar but with a tad more redplating and the base on one broke as it was very weak
-the remaining 12 150s redplated very badly as did the 120s


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PostPosted: 18 Apr 2017, 05:21 
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The attachment shows one of the three faulty 150s redplating at night. The redplating is also clearly visible during the day


This post has a file attachment. Please login or register to access it. Only Registered Members may view attached files.



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PostPosted: 18 Apr 2017, 17:19 
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Hi, A picture is worth a 1000 words. Ugh. The fact that some tubes work and many don't makes me think there is a problem with the tubes. If all did it then the finger could point somewhere else. Keep us posted on the pending build and whether or not the problem occurs there too. If it does then I would conclude that TS is making junk. There are too many successful diy and kit builds out there to expect a circuit issue. And as always there is no way to get more heat out of a tube than the amount of energy you put in. It can't dissipate more than you feed it and if it gets red below the rating then they are IMO defective. Unfortuantely this leaves us with a dead end as there is only a sole source. I may have to design a quad KT88 amp to get the power level desired and stuff the 120 and 150s in the bin.

Good listening
Bruce

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