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Old 16th February 2013, 09:11 PM   #41
midmoe is offline midmoe  United States
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ketjie, again, thank you for the lovely drawing...I did notice that there were no 120 ohmers in series between the screens. (probably don't need them now anyway) Forgive my badly photographed, blurry pencil drawings. I shall upload power supply and short movie soon..... midmoe

Last edited by midmoe; 16th February 2013 at 09:17 PM.
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Old 16th February 2013, 09:22 PM   #42
cnpope is offline cnpope  United States
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chris each tube looks exacly as the brighness level as if in 6.3 vac setup.....regardless of what the meter says, if the fils glow just right, the voltage has got to be right. (each tube shows 10vdc on my vom meter)
Well, as I mentioned before, you won't necessarily get a very meaningful result from a simple measurement of voltage, for the chopped sinewave. However, if your voltmeter is a "traditional" one with an analogue mechanical meter, then on DC it is probably giving a reaonable representation of the time-average of the voltage. The voltage on one of the nominally 12.6V tubes will be a chopped sinewave with a peak amplitude of about 34V, and that time averages to about 10.8V, which is indeed roughly consistent with your measurement.

However, the rms voltage for the chopped sinewave comes out to about 17V, and this is what matters as far as the heating effect is concerned. So you are in fact running the tubes at the equivalent of roughly a 17V rms sinewave. This is considerably higher then the 12.6V they should be getting.

As said before, inserting the diode halves the power to each tube. If you shorted out the diode (not recommended, of course!), each of those tubes would be getting about 25V rms and therefore four times the proper power dissipation. Restoring the diode means the power dissipation is therefore instead twice what it should be. So they are definitely being considerably overrun.

Chris
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Old 17th February 2013, 12:10 AM   #43
midmoe is offline midmoe  United States
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chris. I would suggest you build a similiar lineup and see...it simple enough. I've been in electronics long enough to see a normally lit tube, from a distance of at least 25 feet. Now, whatever the meters or guides say, this thing sits here and looks fine to me. How can this be reconsiled? Seriously, build it and prove me wrong...I'd like that....midmoe
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Old 17th February 2013, 01:08 AM   #44
midmoe is offline midmoe  United States
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apparently I had my sunglasses on when conducting series string experiment...a thousand apologies...switching to regular prescriptions has proved I am wrong..midmoe
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Old 17th February 2013, 02:27 AM   #45
cnpope is offline cnpope  United States
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apparently I had my sunglasses on when conducting series string experiment...a thousand apologies...switching to regular prescriptions has proved I am wrong..midmoe
Glad to hear the law (of physics) is being upheld! Add another 25Z5 in your chain, and all should be just about right...

Chris
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Old 17th February 2013, 04:18 PM   #46
midmoe is offline midmoe  United States
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laws of physics are temporary approximations...25Z5 ? I am out of addl. 25Z5s, will chech this out. Probably will end up getting some nichrome wire from edmund scientific and build my own ballast "tube" as, ascetically I want only one more opening in the top. thanks. was thinking I might be "series strung up" in here when discovering when I had rushed back to the terminal to erase previous entry...and began deserved intellectual "woodshedding" as the little edit icon was gone. what about the whole voltage depth/ current depth thing? Am I again out of my "depth" ? transistorificationing some innocent tube?
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Old 17th February 2013, 05:46 PM   #47
cnpope is offline cnpope  United States
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Originally Posted by midmoe View Post
laws of physics are temporary approximations...25Z5 ? I am out of addl. 25Z5s, will chech this out. Probably will end up getting some nichrome wire from edmund scientific and build my own ballast "tube" as, ascetically I want only one more opening in the top. thanks. was thinking I might be "series strung up" in here when discovering when I had rushed back to the terminal to erase previous entry...and began deserved intellectual "woodshedding" as the little edit icon was gone. what about the whole voltage depth/ current depth thing? Am I again out of my "depth" ? transistorificationing some innocent tube?
I'm not sure I'm catching all the nuances here...

Anyway, all you need is that a 120V rms sinewave becomes about an 84V rms chopped sinewave if you stick a diode rectifier in series. The rms voltage is what matters as far as heaters are concerned, regardless of the shape of the waveform. So a 12AU7, two 12BH7's, and two 25Z5's would, for example, be about right. Or anything else you care to string together (all the same current), as long as the total is about 84V.

Chris
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Old 19th February 2013, 02:18 PM   #48
midmoe is offline midmoe  United States
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correction and revision
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File Type: jpg Picture revision and correction.jpg (473.7 KB, 150 views)
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Old 19th February 2013, 04:46 PM   #49
cnpope is offline cnpope  United States
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correction and revision
It's a bit hard to read the schematics you've posted. Is that a pinhole camera you are using?
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Old 19th February 2013, 06:09 PM   #50
midmoe is offline midmoe  United States
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no, just a pinhead cameraperson. Also failed to upload correctly short video...it seemed to go in alright, but should be here by now...wierd thing, when I was playing it back the sound went at speed, but video was on different time reference, maybe 1/3 speed.....was afraid something wasn't going work, as was first video upload attempt. I did the remake of the screen ckts...seems to have made no problems, but difference too small to detect by ear...creeping towards perfection... Plus I corrected a connection drawing problem in the grid of the lower, last, BH7....from first schematic...ketjie fixed it in her's.....the 14 megapixel camera I just bought took a pretty good video, if it ever gets there.....midmoe
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