Putz, I sorry you are having only around 1K hours.
I sure If you would afford use a soft start and a afew time of pre-heating you will had multiple thousands hours as Joule-Electra.
J-E claim its 6C33 tubes last 5K to 10K hours in its OTL amps, the power on procedure are detailed in this test(very simple, since the amps use a Variac):
Knowing that, I would turn the dial for 10-15 seconds until I reached that point, then use the voltage readout to pinpoint the precise placement for the beginning of a listening session. As the tubes heated up, I would go back in 30-60 minutes and fine-tune the voltage... no problem at all. Very quick and easy, once you got the hang of it.
joule
I more confident the now the Michael Boele datasheet procedure is the way to go.
Thanks for informing.
again >1000 😀
btw there is a difference between a working tube and a tube with the same spec as original and still working
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Just found this info at page 65 of RCA Transmiting Tubes book as a general rule:
FILAMENT HEATING TIME
Voltage should not be applied to the plates or anodes of vacuum, etc tubes until the filaments or cathodes of the tubes have reached normal operating temperature.
http://www.tubebooks.org/tubedata/tt4.pdf
The second paragraph of this topic is also interesting.
FILAMENT HEATING TIME
Voltage should not be applied to the plates or anodes of vacuum, etc tubes until the filaments or cathodes of the tubes have reached normal operating temperature.
http://www.tubebooks.org/tubedata/tt4.pdf
The second paragraph of this topic is also interesting.
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Actually, that wasn't a general rule- your substitution of "etc" for the actual words is... interesting. Further, the text that you excised states that any necessary delays are given in the Data section. The 866 data section is a perfect example of that restriction in the context of the chapter you cited (which was about rectifiers, not signal tubes).
In the rare cases that tubes need to be preheated, their datasheets indicate this fact. Your "cite" is completely consistent with that.
It's not a general rule. If you quote something, quote it right and don't leave stuff out to support your own personal argument. The actual text says "(except receiving types)", plus it's in the 'rectifier considirations' chapter. Not general at all.
Pretty much. The text you quoted is from the 'Rectifier Considerations' section of the handbook, specifically states 'except receiving types', and further specifically states that minimum heating times for the individual tubes are given in the tube types section.
-Pat
These claims are useless.
If is not a general rule, it means nothing against the conservative principle of good care to obtain a long tube life.
When they're based on blatantly dishonest quoting to try to support an incorrect argument, yes indeed, they are useless.
The issue is real but the effect is insignificant for a low power tube. Once you get into tubes that use kilovolt class power supplies the effect becomes important. These would be radio transmitting tubes. Audio tubes, even big ones never have a problem. And these preamp tubes never really get very hot.
If you want to make the tubes last nearly forever simply keep the heater voltage just under 6.3 volts. The tubes are spec'd for pls/minum 6.3 volts so 6.0 volts is fine. At that voltage you can run them 24x7 for decades.
Don't worry about "thermal shock" on a device that takes under normal use 30 seconds to warm up. Trust that the engineers designed the thing correctly. The fact that it takes a full 10 to 30 seconds kind of tells you they thought of this and got it right.
Transmitting tubes that operate north of 1000V, and that have W-Th filaments. In that case, cathode stripping can be a problem. It's not a problem at all with small signal types, and most audio types operating at 400V or lower voltages. Here, cathode stripping is never a problem.
For audio applications that operate off much lower voltages, the only reason to preheat is SS power supplies, and the need to avoid over voltages in DC coupled stages while cathodes are cold. If your PS uses vacuum diodes, then there is no need to preheat even if you DC couple.
Some types need to preheat, but the spec sheet will tell you if that's the case. One such type is the 6AS7 -- a series pass device with unusually heavy insulation between the cathode and heater since it needs a high Vkh tolerance, as the cathode is way above the heater when using it for its intended purpose.
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That is 100% true. But look where it was printed in the TRANSMITTING tube book. There is no such warning in the recieving tubes book.
If yu want the definitive answer about tube life and failur causes read this book:
http://www.tubebooks.org/Books/Atwood/Tomer%201960%20Getting%20the%20Most%20Out%20of%20Vacuum%20Tubes.pdf
I think it is the only definitive collection of what is known on this subject.
The short answer for those who don't want to read: "keep the heater voltages down near the low end of the specified range." This alone matter more then everything else as it lowers the operating temperature. But do stay within the +/- 10% range or whatevr is spec'd for the tube
That said, I've experimented with 12A*7 type tubes and found they run just fine at 5.5 volts. They are spec'd for 5.67 volts. I typically run them in amps I build at 6.0 volts so there is room for some "sag" in the AC mains. You can adjust the voltage with a big power resister of (say) about 0.1 to 0.47 ohms in series with the heater loop.
I build the amp normally then power it up and wait for it to warm up and even put a signal on it. Then measure the heater volts and the AC mains volts and then decide on a resister value and take care that the system will still be in spec with the lowest expected AC mains voltage. I like to think the heaters will be at 5.7 volts if the AC drops to 110 volts. But some time compromise but never allow the volts to go over 6.3. Over voltage is common if using older transformers so check.
There is a lot of misinformation on the web and VERY few people who post on the forums have measured anything themselves. I doubt anyone here has a statistically valid sample size for tube life. Few people have run hundreds of tubes for tens of thousands of hours. Read the book it was written back when people actually did those kinds of tests.
But with heater voltage that low, it would be expected that the tube will behave differently?
The 12AX12 data sheet says 6.3 volts plus or minus 10%. This means the tube will run and meet all the data sheet performance graphs if the heater voltage is between 5.67 volts and 6.93 volts
I will say that at 5.7 volts the ones I tested work fine. I set them at 6.0 so that I have a 0.3 volt margin. This is 5% under 6.3 and well within specs.
I have tested them in a breadboard setup and found that 5.5 volts works too but I would not suggest it. Perhaps the tube I tested was special?
The reason to run the lower voltage is simply to make them last even longer.
Read this page where is says "Voltage Considerations"
The Valve Wizard
Thanks for the link, I already had this book in paper, but I will download it now for more find facility.
Appreciated.
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