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Post by jazznoise on Sept 7, 2015 0:16:38 GMT -6
Welp, my brain imagined that I see. My bad!
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Post by deepdark on Sept 7, 2015 6:51:19 GMT -6
You tried another tube right? Note yet. I wanted to be absolutely sure my circuit is ok before swaping tube. Is a damaged or non working tube could increase current at thé anode resistor? Even voltages are OK? Thé resistor will evacuate thé over current on form of heat? |
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Post by deepdark on Sept 7, 2015 6:53:04 GMT -6
Welp, my brain imagined that I see. My bad! No trouble. Thanks for thé help by the way. |
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Post by jeromemason on Sept 7, 2015 11:00:47 GMT -6
You tried another tube right? Note yet. I wanted to be absolutely sure my circuit is ok before swaping tube. Is a damaged or non working tube could increase current at thé anode resistor? Even voltages are OK? Thé resistor will evacuate thé over current on form of heat? Tube would be the first place to start if your voltages are OK. Especially if you're seeing the correct drop over the resistor. My guess would be a short in the plate, causing it to draw to much current. You said 3 watts was coming across that resistor, so if your voltages are correct current is your next place to look, the plate is directly connected to 8k2. Start w/ the tube IMO. |
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Post by deepdark on Sept 7, 2015 11:21:52 GMT -6
Thanks. You're right. I tend to suspec the layout 'till i test all voltages and current. Yes, voltages drop are all good, with ohms law, it gave good current guess. I calculate 3 watts across 8k2 given the reading voltage drop i got (about 165v) which give about 20ma. 165v through 20ma is about 3,3W. So were trouble may be occuring is between 8k2 and the plate? If a short at the plate of the tube is occuring, then what, current will flow from plate to the resistor, or current will build up at the plate resistor? As i said, all voltages look good and ohms law tells me current across resistor looks fine.
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Post by deepdark on Sept 7, 2015 11:32:04 GMT -6
Oh and by the way, is it possible a tube consume, say, 20ma instead of the 18,5 ma? So about 1,5ma. Not a big deal. I guess different batch, brand, different reading and the fact resistors never read exactly the right value, right?
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Post by jeromemason on Sept 7, 2015 11:41:09 GMT -6
If the tube has a short, or there is something damaged around the plate and you're running 165v into a dead short it will demand more current through that resistor and cause it to overheat. I would almost guarantee it's the tube because when you removed it the resistor was fine.
What was your reading at the Cathode?
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Post by deepdark on Sept 7, 2015 11:42:39 GMT -6
Cathode was about 3,8 or 3,9 v. Schematic recall for about 3,7v oh and c5 (1uf) block all dc so no leakage here
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Post by jazznoise on Sept 7, 2015 11:50:38 GMT -6
Doesn't sound like a dead short if it's only drawing 1.5mA higher than it normally should,though, does it? That's only 10% error. Still if the 5W is still producing smoke that would imply the current going through it is much higher than 3.3W Something is amiss here.
If you've a spare tube it's definitely worth trying it.
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Post by deepdark on Sept 7, 2015 11:53:53 GMT -6
1,5ma is only a rought calculation within ohms law. I didn't measure it yet. Its only the consumption given the actual vdrop and the resistor value. So yes, it could be a dead short because vdrop is allright and all other one. So excess curent would evacuate in form of heat i think.
1,5ma could be explain by the resistive parts of the circut, the layout, the fact tesistor never has the exact value they are rated,mthe tube itself, etc.
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Post by jazznoise on Sept 7, 2015 12:00:12 GMT -6
You didn't say that.
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Post by deepdark on Sept 7, 2015 12:04:59 GMT -6
Oh and by the way, is it possible a tube consume, say, 20ma instead of the 18,5 ma? So about 1,5ma. Not a big deal. I guess different batch, brand, different reading and the fact resistors never read exactly the right value, right? That is what i said. The 20ma was a rough calculation of 165vdrop across a 8k2 resistor. Then comparing with the schematic value, i was simply thinking about the fact that different tube brand and batch, nos or brand new, could cousume more or less of the specified current. |
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Post by deepdark on Sept 7, 2015 12:06:14 GMT -6
Oh and the fact my b+ is a little higher than the schematic could also influence that.
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Post by jeromemason on Sept 7, 2015 17:40:24 GMT -6
You replace the tube and I bet your issue goes away. If your B+ was 30 or 40v higher than rated then I would understand it getting warm.... but with a normal B+ everything should run cold. Simple fact that you taking the tube out eliminates the heat is a dead giveaway something is screwy there. 8k2 is directly connected to the plate....
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Post by deepdark on Sept 8, 2015 15:02:47 GMT -6
No luck with the tube. I replaced the e88cc and it is still hot and smell. Mo more fume, thought. C4 and c5 bloc dc, all voltages are spot on. B+ is 305v. I'll have to test current before and after 8k2 to see of there is something weird.
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Post by EmRR on Sept 8, 2015 15:08:14 GMT -6
anything is possible. suspect everything.
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Post by deepdark on Sept 8, 2015 15:24:07 GMT -6
Allright. Basically, since voltages looks good everywhere, i'll have to check current at some point around e88cc i guess, once i get where it all screw off things?
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Post by deepdark on Sept 8, 2015 15:25:55 GMT -6
Is heaters can have something to do? Exemple, if they are at 7,3v?
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Post by deepdark on Sept 8, 2015 16:44:39 GMT -6
One thing i'm thinking. The original schematic recall 30ma for a 400v dc psu. After the rectifier i got 395v. Maybe i'm about 30ma and the excess of current is heated through the 8k2 which set it to the edge of it's limit. Just some thoughts here.
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Post by jazznoise on Sept 8, 2015 17:19:15 GMT -6
I know it's annoying, but measure the currents. Speculating won't get you much further than you already are.
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Post by deepdark on Sept 8, 2015 18:30:15 GMT -6
First current measurement, power supply to the junction of 8k2 is 21,4ma. Looks pretty good so far. I changed the ef86 tube, change 8k2 for another one, changed C5. No luck for now, I'm waiting for the caps to discharge before taking current straight after 8k2.
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Post by deepdark on Sept 8, 2015 18:51:55 GMT -6
other side of 8k2 is 19,6ma, pretty spot on, too...
I let it run for about 5 minutes, 'till the resistor began to smoke and there was no change in the current value. It wasn't increasing.
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Post by deepdark on Sept 8, 2015 19:36:18 GMT -6
Now I took current between R11 and R7, I got 1,7ma. Again, pretty spot on.
C6 has been changed, just in case, too.
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Post by deepdark on Sept 8, 2015 20:02:04 GMT -6
Curent after R9/jonction of C4 and R8, read 0 (my dmm isn't that precise). I calculated before a drop of 43v through R9 (1M6) which gave a pretty low current, so here it looks to be right, too. I begin to suspect my sanity lol. But seriously, I really don't see what happen here.
Current is right, at least around e88cc. current is spot on before and after 8k2, so how can we eat up such power if current reading is correct? Wire gage? There is no sign of dc after each caps, too.
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Post by EmRR on Sept 8, 2015 20:20:38 GMT -6
If the wire ate the current, there'd be nothing for the resistor to smoke. The resistor is about all that's left from your poking, so why trust the resistor? Get a different type, get a higher wattage, whatever, those may be counterfeit or mislabeled. 2x current is always recommended minimum in power resistors, and you are under that.
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