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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 9:12:41 GMT -6
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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 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 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 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 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 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 10:21:48 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 10:16:14 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 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 deepdark on Aug 23, 2015 13:14:38 GMT -6
Anyone?
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Post by deepdark on Aug 22, 2015 14:45:15 GMT -6
Hi.
quick one for you. I'm making a p2p redd47 with phantom power. The original schematic recall for a 100ma fuse but on the dc side. It will of course be higher in the ac side. The unit consume sbout 20ma, phantom power about 10-15ma and heaters 500ma. Am i right to think about a 250ma fuse or i should get something higher?
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Post by deepdark on Aug 16, 2015 4:29:12 GMT -6
Other than that, do you have anything else in mind of trouble lie somewhere into what i already think?
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Post by deepdark on Aug 14, 2015 9:08:56 GMT -6
and concerning my psu, with the 4 large 47uf capacitor, I don'T think it is the trouble we got here (in term of ripples shot into the circuit)!? Maybe too much filtering, though. I could replace the last 47u with something like a 22u.
The way I see it, is that 6SQ7 is controled by the output of V2. A portion of the signal is send from V2 pin 8 (output) to V4 via a coupling cap (C5) and R10 (threshold), which set the how hard we will limit. The amplified signal then exit at diodes plate 4/5, coupled with C6 and go through R11, and then to C1/R1 and attenuator pot. So where appear the motorboating? At the limiting stage, or after the amplification stage of V4, so between output of V4 (pin 4/5) and input stage? If occuring at the limiter stage, so having a good 6sk7 matched pair would help or since we only take output of V2, imbalance shouldn't be an issue?
I just try to figure out where did the motorboating start
Another thing I'm suspecting is a not high enought power resistor. Exept the big 10 watts resistor and my psu ones that are 1w, all my other résistors are 1/2W. For exemple, R7 drop about 51V/27k = 1.89ma. 51v at 1.89ma should gave me a power rated low enought to use a 1/2w resistor. and R8 (current ctrl) is 2 watts. So probably not the culprit here.
one possibility is the shield. Maybe if i strap it straight to the tube socket mounting bolt it will shorten the run and help. Or maybe one of my lytic cap is leaky, or c6.
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Post by deepdark on Aug 14, 2015 8:42:03 GMT -6
Looking now at the 6SQ7 section which is motorboating. Looking first at the voltages, my plate is spot on 140V, so my current shoudl be ok there. I adjust pin 3 at 2.5v via the current control. The only place is the diodes section pin 4/5. I measured -0.8v instead of -1.42v. This is where I think I could have a trouble. Some thought about that part. Maybe C6 is where I got trouble. Maybe I should install it closer to the tube instead of mounting it on the turret board. Maybe distance is important here. If so, the trouble would sit before the 6sk7, so before compression stage, isn't it? Or maybe better 6sk7 tube match would help. basically, the diode are wired to send a half wave signal, so only one portion of the wave is then send to C1/R1, isn't it?
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Post by deepdark on Aug 12, 2015 18:41:00 GMT -6
Houra, I run the unit without the input transformer and it was teh culprit. Frequency is flat as hell. a 3-5 db drop at 50hz and about 7db at 17khz. So now, I need to convince edcor to send me another one XD. I just tested out with another edcor transformer and it is allright. So we find the culprit.
Next step, finding the culprit of the motorboating XD
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Post by deepdark on Aug 12, 2015 9:16:36 GMT -6
allright. I'll plug it into an mic input, which is 3k and that should be a little better for testing. removing the 6sq7 will basically force the signal to flow from input amplifier to the output, no current control, etc. isn't it? If things remain the same with or without, then the trouble of low end loss will not be into the side chain circuit but localised between the input and output stage. And by removing the input transformer, and passing signal straight to the dual gang pot, we will see if thing change according to the frequency response. If not, then trouble is after the input transformer, but before, the output one. If I try another output transformer and things do not change, then the trouble sit between the 6SK7 and 6SN7. Am I allright?
Next time, be sure I'll not buy another one. I'll stick to Cinemag
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Post by deepdark on Aug 12, 2015 8:30:36 GMT -6
oh and I forgot to mention, with the lows lost, came a bump at around 1Khz. Frequency start to fall at about 500hz. This is what I remenber from my test and forgot to list it here.
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Post by deepdark on Aug 12, 2015 8:23:21 GMT -6
I'm being thinking about the fact I'm loading the output at 10K, this is probably not a good thing. If I force my secondary to be 600ohm, ( strapping a 660ohm resistor across the secondary) could it help of it will just fucked it up even more? I don'T think the load will be the exact square root at the primary of the secondary, isn't it?
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Post by deepdark on Aug 12, 2015 7:58:25 GMT -6
holy crap, really? last time I ever got them. I'll try the current balance pot tricks and then, swap out the input transformer, and then the output if nothing change. Now that explain the ridiculous price (though the shipping is real robery)...
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Post by deepdark on Aug 12, 2015 6:14:59 GMT -6
I've just order the wirewound lienar pot and I just got new couplign caps, 0.22u instead of 0.1u. I'll try them out, too, in case one of them (maybe C5) goes in trouble
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Post by deepdark on Aug 12, 2015 5:42:07 GMT -6
I'm thinking about something. Maybe the way I strap the current control and treshold pot have to do with motorboating trouble. Instead of running a pair of wire from 6sq7 pin 3 to the wiper of R8 and pin 1 of R10, I ran it straight to R8 and then strap the wiper of R8 to R10pin 1. Maybe I should run a pair of wire from pin 3. Another one, do R6 need to be close to R8? Mine is on teh same psu board and I run wires from it the the other extremity of the case to the audio board. For now, these are my thought. R8 is adjuste to 2.5v, according to the manual.
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Post by deepdark on Aug 12, 2015 4:41:49 GMT -6
Alright ill try that out. And if it is not the trouble, maybe the trouble came from the circuit between the 6sk7 and 6sn7. Coupling cap, for exemple. They are the right value but we never know. Is it possible one of the transformer just fucked up my lows, just out of curiosity?
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Post by deepdark on Aug 11, 2015 19:48:03 GMT -6
Thank Doug for your help, really. You have no idea how I appreciate it. So, it's allright for the meter, I'll work it out when I'll sort out the motorboarting trouble and the low end trouble. So here, we talked about current balance through the output transformer. So I should implement a curent balance pot and tweek it until got back my low end, which will tell me that I have some sort of balance in there. Just to be sure I'm following you, we are talking about dc current? To be honest, that part is a little obscur to me. Basically, the current balnace pot should be strap at cathode of 6sn7, so pin 3/6, right? If possible, could you explain to me why the imbalance would sucked such a large portion of the frequency? As it acting like a hpf loool. I'll take a further look at the sidechain circuit. Could it be simply the tube which is defective?
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