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Post by deepdark on Sept 5, 2015 9:37:51 GMT -6
Hi
I just make a redd47 and so far, voltges are all spot on. My B+ is 305v. But one thing weird is that 8K2 5W resistor get pretty hot after 2 minutes and begin to smoke a little. Voltages at E88CC are all spot on, too. Is it possible my wire feeding B+ is too smal (22ga, rated 300v) to handel it? The power supply is a simple 5 stage rc filter made of 1K-1W resistors and 47uf caps.
On another note, is there a tricks to make the caps discharging quickly while power off the unit. A kind of bleeder resistor?
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Post by EmRR on Sept 5, 2015 10:05:26 GMT -6
it means the tube is drawing too much current, assuming that's the right sized resistor. Sounds like it is. It's a regulated supply, so voltage will not fluctuate.
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Post by deepdark on Sept 5, 2015 10:16:14 GMT -6
I don't use the original supply. It's only a rc filter made of 5 stages, so not regulated
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Post by deepdark on Sept 5, 2015 10:21:48 GMT -6
I found a missing link at the gain selector. The plate wasn't linked to pin 3 on the switch, so probably c5 couldn't discharge and accumulated current. Can't test for now though.
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Post by deepdark on Sept 5, 2015 10:39:11 GMT -6
Another thing a found is that 1m6 resistor and 330k don't read good on my dmm. 1m6 read about 330k, but it's the good value resistor and 330k read 270k. So that is why i suspect a missing wire.tube plates are spot on. The trouble must lie between e88cc plate and ef86 plate (1m6 resistor and 330k resistor) and c5. C5 go to the gain selector plate/pin 3 which has that link missing.
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Post by deepdark on Sept 5, 2015 10:50:37 GMT -6
Damn, i just thought about the fact i just not install yet any input transformer (didn't receive yet). So input tube grid as no reference to ground. Might be the trouble here i think, if we inject current at anode but there is no reference to gnd at the input grid, no load, i guess current build up inside the tube And it could explain why my psu filter caps won't discharge totally, because at one point, current cannot return to 0v (in my case, input grid), so caps get charged. Right?
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Post by deepdark on Sept 5, 2015 12:22:10 GMT -6
Hmmm i tried what i said but no luck. One weird thing is that heaters measure 0,2v...really weird. Any idea?
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Post by jazznoise on Sept 5, 2015 15:54:38 GMT -6
Can't give any direct advice, but I will say that it's common for components to measure differently to their real value due to the surrounding circuitry. Thevenin equivalents and all that.
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Post by deepdark on Sept 5, 2015 16:07:17 GMT -6
Can't give any direct advice, but I will say that it's common for components to measure differently to their real value due to the surrounding circuitry. Thevenin equivalents and all that. [br Yeah that is right. I just tried the other main board I had (I'm building 2 redd47 and I had a main board stuffed but not connected yet) and I measure exactly the same result. So the culprit isn't there. For now, I disconnected the phantom supply from the main, disconnected the ht from the main board and took off the tubes, to test the supply unloaded. I got 7,85v at filament (which is good, given the fact it's unloaded). B+ gave 445v after the rectifier, which I guess is ok, since we are unloaded. Quick one, if I'm unloaded, then I'll got the same voltages after the rectifiers than the last dropping resistor, right? If I'm right, I would say my main transformer is ok, as well as my psu. Next step, I'll try to load B+ to the main circuit, but without the tubes. If I don't smoke anything, then I'll try with the output tube, if t smoke, then the trouble should lie around that one (or the tube itself). If it doesn't smoke anything, then I'll insert the input tube. Is it the good way for troubleshooting that kind of issue? |
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Post by deepdark on Sept 6, 2015 6:43:58 GMT -6
Oh and one thing i'm trying to understand. If my voltages were spot on, but e88cc plate came really hot (when touching it) and a light smoke came out, how can this circuit drawing out too much current? The exces of current is evacuate in form of heat? What can be the cause, given the fact all component are good values, and continuity test show no layout error along the schematic. Bad tube? It's a brand new JJ.
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Post by jazznoise on Sept 6, 2015 8:20:38 GMT -6
Well I don't know what schematic you're using, so I'm reluctant to make comments. The one I have here has current readings and test points. If you have the test points that will let you know just fine. Please post the schematic you're using, otherwise we're flying blind. This one seems to suggest that it's an 82K resistor and not an 8K2 resistor.  |
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Post by deepdark on Sept 6, 2015 9:00:01 GMT -6
This is the schematic i use, but mine has 8k2. With ohms law, we know we have to drop about 160v ghrough the resistor. 160v/18ma gives about 9k. 82k would give a 1/10 current (1,8ma)
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Post by deepdark on Sept 6, 2015 9:12:41 GMT -6
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Post by jazznoise on Sept 6, 2015 9:38:05 GMT -6
Yeah I thought the 82K value was ridiculous, simply because of the voltage noise alone. Have you tried measuring the current? I know you'll have to break the circuit (can't do current measurement in parallel) but with R2 and R10 in parallel it's always going to measure an incorrect value, and this is the only way to really confirm if R10 is doing its job or not.
If the reading is (much) higher than what's stated, make sure C5 is blocking DC or it's going to barf current through the primary of T2, likewise C4 being shorted will screw up the tube bias. Check polarity too, obviously.
After that it's a case of going from the start(from a DC perspective) and checking the voltage drops across everything and seeing if they're correct. That's when troubleshooting gets *really* annoying.
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Post by svart on Sept 6, 2015 9:46:06 GMT -6
I see the original schematic show 290v through 8.2k with a drop of 152v to 138v at 18ma..
What is the voltage your power supply produces at the input of the 8.2k resistor while loaded?
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Post by deepdark on Sept 6, 2015 9:45:57 GMT -6
Thanks. I'll see what happen while starting with tube but b+ not connected to the circuit. If heater looks good, then i'll add b+ without tube. From there i'll put tubes from output to input one at a time. I'll also disconnect one side of r11 to measure current (in serie of course). Thats what you were saying, disconnectin r11 from obe side to check current at the resistor?
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Post by deepdark on Sept 6, 2015 9:46:59 GMT -6
While loaded it's about 310v
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Post by deepdark on Sept 6, 2015 11:35:02 GMT -6
ok I make some more test. Put the B+, with no tube, it's the same as running unloaded, no smoking resistor, of course. Then. after discharging the psu caps, I pull in the tubes and make some measurement. As I said, all voltages are spot on.
E88CC plate = 143v
E88CC cathode = 3,9v
EF86 Anode = 82v
EF86 grid 3 (pin 1) = 101v
Ef86 catode = 1,6v
R11 vdrop = 165v
R7 vdrop = 83v
R2 vdrop = 136v
R12 vdrop = 116v
R9 vdrop = 43v
R14 vdrop = 8v
8K2 didn't make smoke that time, but it remains pretty hot and there is a burning odor. It's a wirewound with a flame retardant coating on it.
What do you guys think about those values?
E88CC side of C5 is 143v, the other side read 0v (so C5 bloc all dc current)
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Post by deepdark on Sept 6, 2015 12:39:59 GMT -6
By the way, according to maths, my power cunsumption acriss 8k2 loks to be 3w. According to what you think, i'll have to check current between psu and the juction of r11 and r7' to be sure to read about 20ma. And current after r11 to the joction of plate/r9/c5. Should be about 18,5ma. If i consume more than 3w, let's say 6w through r11, then i should read about 35ma.
but i'm pretty sure b+ will be right for one reason. My psu is RC topology made of five section of 1k resistors/1w and five caps of 47uf. After the rectifiers i got 395v and i need to drop about 95v, at 20ma. 95v/20ma gives 4700k/5 = 950ohm each. Total piwer is 95v x 20ma = about 2w. Less than 1/2w per section and i put 1w resistors.
Is the wire i used can be the culprit? I put some 22ga/300v rated.
And my heaters are at about 7,3v
lastly, how long after shutting off filter caps take to discharge? Do they fully discharge over time?
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Post by NoFilterChuck on Sept 6, 2015 15:21:23 GMT -6
You should be asking this on group DIY on the redd47 thread.
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Post by deepdark on Sept 6, 2015 16:16:46 GMT -6
Yup, once the maintensnce will be finished
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Post by deepdark on Sept 6, 2015 16:36:56 GMT -6
One thing i'm thinking. First start up, i wired b+ the other side of 8k2, so straight at the anode. I'm wondering if i damaged the resistor or something else
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Post by jazznoise on Sept 6, 2015 16:47:46 GMT -6
Since you said it was measuring 7K, that's unlikely. The drop in resistance is almost definitely due to the multiple parallel paths from B+ to ground.
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Post by deepdark on Sept 6, 2015 16:58:14 GMT -6
Since you said it was measuring 7K, that's unlikely. The drop in resistance is almost definitely due to the multiple parallel paths from B+ to ground. What do i said measuring 7k? |
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Post by jeromemason on Sept 6, 2015 20:22:17 GMT -6
You tried another tube right?
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