Bottlehead Forum
Bottlehead Kits => Eros Phono => Topic started by: Steve Reese on January 19, 2013, 05:22:06 AM
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I'm on step where you install the 12BH7 in order the measture the voltage from D1 and D6. At first I didn't get anything, and this morning I resoldered all red wires and the two large resistors on top of the board that are twisted together since they had some dark matter in them somehow... one even had came apart somehow. Retouched it and tried again, and wow, I got the 225V... the 4 diodes were glowing and the tube was glowing. I turned it off, unpluged the power cord, switched to red clip to the wire attached to D6, and now it stays steady between 330 to 335. I've retouched D6 and D4, and some more connections... I don't know what else to try. If anyone has any suggestions, I'd greatly appreciate it. Thanks to all who may reply.
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You did not say, but I guess you got the 225v at D1 at first, then failed to get it at D6. Am I correct? If so, that indicates one channel's regulator is working and the other isn't.
Measure voltages on the 12BH7 socket pins 1-2-3-6-7-8. That will tell us what the tube is doing, and might lead to where the problem is.
Incidentally, you said "...switched to red clip to the wire attached to D6" - be aware that wires are only attached if the solder connection is good, and it is sometimes necessary to measure at the actual socket lug instead of the wire that appears to be attached to that lug. I only stress this point because such a large proportion of wiring problems end up being solder joints that appear good but aren't.
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Sorry it took me so long... had family obligations. Here are the measurements:
D1 - 352
D2 - 0
D3 - 0
D4 - 0
D5 - 0
D6 - 352
D7 - 0
D8 - 1
at the 270 ohm it's 352: at the 6.3V both red and black are 0. It's strange how all of the of the voltages were spot on, then only to switch wires, I powered off, switched to D6, and then nothing was right, or as it is now. Here is the problem I had early on in the construction http://www.bottlehead.com/smf/index.php/topic,3671.0.html
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Looks like neither triode is conducting. My first guess is that the heater are not getting any voltage. You should be now have confirmed that the 6.5v heater power is being generated, so look to see if there is an orange glow inside the tube, and if not look at the wiring to tube pins 4/5 and 9.
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Okay, I will, thanks Paul... I'll post after I check them out.
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Okay... I basically rebuilt D tube socket and reattached the shunt regulator board, and I'm still getting a reading of around 330V. When I first turn ON, it will hover around 300, then it slowly goes up to 300V. Is there any readings I can take on the board to see what might be the problem?
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Do you have orange tube glow? (For that matter, is the 12BH7 in the socket?)
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yes, the tube is in the socket, but has no glow... I'm wondering if the pins are spread too wide or something. It does go into the socket pretty easily.
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This is good information. There is a shielded twisted pair wire that goes to pins 4/5 and pin 9 on that socket, they feed the voltage that lights the tube.
On the power supply board, there is a pair of pads that say 6.3VDC + -, can you measure the voltage at those pins?
If you have 6.3V there, there should be 6.3V at the tube socket.
If you don't, let us know what you do have at those pads.
Any other messing around with the C4S board at the tube socket is a waste of time until this is sorted out.
-PB
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Sorry it's taking me so long to get back.... i'm in the beginning stages at work with a company wide computer hardware refresh, so my evenings are taken with that and home duties. I just tested at the 6.5V, and it had nothing. At D1, it was 335V.
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Ok, if there is nothing at the 6.5, there is an error in the components on the power supply board, or there is no AC going to the low voltage supply on the PC board.
The MJE5731A and the LT-1085 chips look the same, can you be sure it's the 1085 that you have soldered to the board and connected to the heatsink?
Also, measure the AC voltage coming into the board between the pads T4/T5.
-PB
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The chip mounted to the huge heat sink is the LT1085, and T4 & T5 are both 5V which make no sense since they were both tested at 9.7V when it's ask to measure them on pg 42 of the instructions.
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Measure the AC voltage between T4 and T5, not the voltage between each of them and ground.
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Both T4 AND 5 read roughly 2.5 VAC. That's with meter ground mounted to #23 ground and reading T4 and T5 individually.
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Put the black probe on T4 of the PCB, put your red probe on T5 of the PCB, then measure AC voltage.
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It reads 7
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Ok, next, double check all the 1N5820 diodes and their orientation. With 7V AC in, the DC voltage coming out will certainly be greater than 0.
After that, set your meter to DC and put the black probe back on ground, then measure the DC voltage present at the banded end of one of the 1N5820 diodes that's closes to the 6.3vDC pads. This will tell you your DC voltage available to the regulator.
-PB
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It reads 9V
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OK, so far this is a good sign, you have the AC coming in, you're making into DC (and enough DC at that), but you have no output from the regulator.
The next step is to triple check the two resistors that nestle up to the 1085 regulator, as they set the regulator voltage.
I would also flip the PCB over and touch up the seven solder joints (2 on each resistor, three on the 1085).
Additionally, the two yellow capacitors on the outside of the PC board are polarized, it's possible that one is in backwards.
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I touched up the 7 resistors and check and verified that the two outer yellow resistors are oriented correctly. Did a voltage check and still no light on Tube or diodes.
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Can you post a photo of the top and underside of the PCB?
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Are these good enough to see?
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If anyone would read this, http://www.bottlehead.com/smf/index.php/topic,3671.0.html, could another big resistor may be compromised?
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Its hard to tell from the photo, but some of those solder connections especially in the middle of the PCB look like they might bridge two traces. I just think it might be a good thing to check with a magnifying glass while waiting on PB and others who are more knowledgeable than me respond.
Ken
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I reviewed the whole thread this evening, since it's gotten rather long. I notice that the regulator 12BH7 was working initially, so the lack of heater voltage now is probably something simple - hopefully, just s single bad connection. Until we get the heater power restored, there is no point in looking for other problems, in fact it's quite likely there aren't any.
I can't tell from the picture whether all four 1N5820 diodes are pointing in the same direction. I'm looking at that because you read 7vAC between power transformer terminals T4 and T5 (or perhaps where they connect to the PSU board, with the same labels). There should be more than 9vAC between those two points. I do not actually think this is the problem, but it's best to be certain. If you still get 7 volts, I'll have to ask if your meter is accurate - test a fresh 9v battery (on DC) to confirm.
There should also be around 9vDC at the forward ends of each of the two diodes that lie nearest the output terminals on the board. I specify both of them in case one is not soldered well - like the large chips, these diodes can absorb enough heat to slow the soldering process.
The terminals on the board labelled 6.3vDC should have 0 volts on the negative terminal and +6.3v on the positive terminal. If the positive voltage is zero, then it may be worth the trouble to attempt to measure the middle leg of the '1085 regulator - be careful there, since it is probably only accessible with a probe, and you don't want to slip and short the pins! Pin 3, which is the one closest to T4/T5, should have 9vDC on it.
I'm afraid those are all the test points that seem to me to be accessible within reason. Make those measurements, in that order, and we should be able to make a good guess as to where the problem is.
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Okay, again sorry it took me a while... I retouched the diodes, and yes, they're all pointing the same direction. After attaching the wires, I measured T5, and it measured just over 9VAC. I measured the outer most diodes, and they measure just over 10VDC. I measured the +6.3 post, and it didn't even read a volt. It has what I think is a solid connection. I then measured what I thought was pin 3 on the 1085 regulator closest to T4,5, and it read just a hair over 9vDC. I just don't get why I'm not getting 6.3vDC......
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My best guess at this point is a cold solder joint on the 1085.
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Okay, I reattached the wires once more and before hand retouched the 1085. And I got the same thing. I wonder when that 100uF 450V cap blew that is also ruined the 1085....?
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The high voltage supply is extremely unlikely to have an effect on the low voltage supply.
Before going to the trouble of removing and replacing the 1085 (it will be neither easy nor fun!), check the voltage at its middle pin as suggested. In fact, check the voltage at each of the three pins - you've already got the right input voltage at pin 3; let's be sure about the others.
The reason I suggest making these measurements is that it worked before, so the 1085 was not "dead on arrival" and it's not that easy to damage it. That makes me think that merely replacing the chip won't address whatever the real problem is. But if measurements can't resolve this, that would probably have to be the next step.
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Sorry.... I didn't read it correctly. Pin 1 reads .4vDC; Pin 2 reads .78vDC; and Pin 3 reads 10.83vDC
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OK, looks like the 1085 is dead all right. Contact Eileen on Monday and she'll send a new one; there's at least a good chance that will fix whatever was wrong.
Meanwhile you can try to remove the old one. Once it's out, read the resistance to ground from pins 1 and 2; they should be 499 and 623 ohms respectively - you'll have to pull the tubes in order to make these measurements (the heaters will short these resistors, which are the voltage divider that sets the 6.3 volts). This check will help assure that this portion of the PC board is working correctly, giving I hope increased confidence that the new 1085 chip will work when installed.
I still have no good theory what happened to the chip, but if a new one works then you don't have to care!
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Paul, let me see if I understand this correctly... Once I take out the 1085, you want me to do an ohm test on it, or once I have the new one in place, that's when I do an ohms test. Cause you're talking about making sure the tube is out cause the heater will short the resistors. Or am I to take the readings from the power supply Pins 1 and 2...?
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You want to take readings on the PC board with the tube pulled out.
-PB (the other Paul)
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oh, where Pins 1 and 2 are respectively... and powered off correct?
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You can find the pin assignment on page 2 for the TO-220 package:
http://cds.linear.com/docs/Datasheet/108345fg.pdf (http://cds.linear.com/docs/Datasheet/108345fg.pdf)
The drawing assumes that the writing on the chip is facing up, so if you have the writing facing up and the hole in the metal tab facing left, the pins go 3, 2, 1, down the right edge of the chip.
-PB
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Okay.... I have tried like crazy to get that huge heat sink out, but no luck. I've tried to remove the two small resistors near the edge of the board, but can't get them out cause for me it's hard try to heat two leads in order to remove them because my thought was to get those out then clip out the 3 pronged 1085 resistor. If anyone would have any experience in removing these parts, please share. I've been out of town for while but plan tackle this again when I get back. Thanks.
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I'd leave the heatsink there, it doesn't need to come out.
Go buy a spring-loaded solder sucker and suck all the solder out around the pins on the 1085, then remove it (removing the hardware that holds it to the heatsink as well).
Same for those two resistors, you can suck the solder out around them, then pull them out.
-PB
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Okay... I've gotten the 1085 resistor in place, along with the two 10uF capacitors which I had to have Eileen send me some after basically destroying them trying to get them out. Tried to get a reading, and once again I get the same high reading on D1. It hovers around 307 for a good 5 seconds, then stops between 325 and 332. It gets the same when I remove the tube. I'm at a loss.
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Okay, I'm begging now... if anyone has an idea what I should check next, please tell me. I keep looking at the big can capacitors wondering if something may be compromised with them. I didn't do anymore checks other than D1 and D6 which were same, so I thought that any other readings I'd be asked previously would also be the same. Any thoughts are welcomed. Thanks.
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Hi Eros fans --
I've built from scratch and modded more gear than I can remember. I'm now in the process of smoke-testing an Eros kit I built for a friend. I would think that following Bottlehead's extremely well-documented manual would result in a first-trial success story. Uh, not quite. :o I'm at a point where I can't seem to see the forest for the trees. :(
The left channel uses the led-biased input stage (to experiment) while the right channel follows the original Eros servo design. I have 1.8v at the L cathode; the R sits at 1.5. The plate voltage on the left is 97, the right is 94. A bit low in each case. BUT, the plate voltages on the EC88 are both 107! That's way off!!! B+ from the power supply card is 221 and filaments are at 6.2. Close enough.
My wiring appears to be spot on. So, what is my problem? ??? (Besides the likelihood of overlooking something all too obvious)
Atom
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So, what are the grid and cathode voltages on the ECC88? And the screen voltage on the EF86's? This is a direct coupled two-stage amplifier, and all the voltages interact.
One possibility, for example, is the bypass capacitor on the triode cathode, which if reversed (it happens!) will drive the tube into saturation. The voltages will give a good hint.
Incidentally, 1.8 volts is high for an HLMP-6000 LED, which is normally around 1.55 volts. 1.55v is a good bias for an EF86 that meets the original specs, but many modern tubes sold as EF86s need an actual bias that is lower; I believe I've seen as low as 0.8 volts. That's why there is a servo in the stock design. Direct coupling is a pain!
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So, what are the grid and cathode voltages on the ECC88? And the screen voltage on the EF86's? This is a direct coupled two-stage amplifier, and all the voltages interact.
One possibility, for example, is the bypass capacitor on the triode cathode, which if reversed (it happens!) will drive the tube into saturation. The voltages will give a good hint.
Incidentally, 1.8 volts is high for an HLMP-6000 LED, which is normally around 1.55 volts. 1.55v is a good bias for an EF86 that meets the original specs, but many modern tubes sold as EF86s need an actual bias that is lower; I believe I've seen as low as 0.8 volts. That's why there is a servo in the stock design. Direct coupling is a pain!
I made a voltage chart, Paul.
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Thanks, Atom. You are right, this is strange and something is not working right. It's still hard to tell what, because the voltages and currents don't add up.
So ... some possibilities:
* I assume since you haven't said anything to the contrary that the LEDs on the C4S boards are all lit with similar brightness - a little brighter on the A side than the B side.
* If the R1 resistor on the C4S boards is off, that would change the current. Check the resistances, R1 (A side) and R1 (B side) which should be 113 and 301 ohms respectively.
* If the resistors are off, that would cause the currents to be off. Check for 27K from C3 to ground, and from C8 to ground - these are paralleled with the 100uF / 160v cap, so it will take time for the resistance reading to settle. Make sure that cap is correctly oriented (yeah I know - you've probably already done that several times by now. But it's still a significant suspect.) Then check the 47K resistors, C1 to ground and C6 to ground.
* Long shot - you posted several times "EC88" which is a single triode - not useable in Eros. I have assumed you meant ECC88 which is also called 6DJ8. The circuit is actually designed around the 6922 or 7308, though the 6DJ8/ECC88 is similar enough that it ought to work.
OK, it's nearly midnight and that's all I have right now.
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Thanks, Atom. You are right, this is strange and something is not working right. It's still hard to tell what, because the voltages and currents don't add up.
So ... some possibilities:
* I assume since you haven't said anything to the contrary that the LEDs on the C4S boards are all lit with similar brightness - a little brighter on the A side than the B side. [ ------------------ By my subjective observation, Paul, they all look very much alike.]
* If the R1 resistor on the C4S boards is off, that would change the current. Check the resistances, R1 (A side) and R1 (B side) which should be 113 and 301 ohms respectively. [ ------------------------ I measured every resistor on the C4S boards and all were within fractions of their indicated value.]
* If the resistors are off, that would cause the currents to be off. Check for 27K from C3 to ground, and from C8 to ground - these are paralleled with the 100uF / 160v cap, so it will take time for the resistance reading to settle. Make sure that cap is correctly oriented (yeah I know - you've probably already done that several times by now. But it's still a significant suspect.) Then check the 47K resistors, C1 to ground and C6 to ground. [ -------------------------- All OK there. ]
* Long shot - you posted several times "EC88" which is a single triode - not useable in Eros. I have assumed you meant ECC88 [ ---------------- Yup! Definitely an ECC88. ---------------------- ] which is also called 6DJ8. The circuit is actually designed around the 6922 or 7308, though the 6DJ8/ECC88 is similar enough that it ought to work.
OK, it's nearly midnight and that's all I have right now.
Well, Paul, thank you very much, that was lot of good late night advice. I ultimately found my problem! The resistor check had me stumble over it.
I'd said previously that following the manual's instructions (kudos to its authors) should result in a first-attempt success at a functioning Eros. I still strongly abide by that.
In MY case, however, I didn't quite follow some important details. ::) The MPS4250's are to be installed so that "the flats of the bodies [are] facing in toward each other." Those words and the associated picture make it quite obvious how these li'l guys should sit on the card. But, n-n-o-o-o-o-o.... I had to do it differently. I mounted both A-Q1's so that they're marching off the card in the same direction as the B-Q1's. Wrong! What a bonehead!!! :-[
Correctly reinstalling the two transistors brought everything up to spec. Almost. (Both channels sound very good!) The cathodes' led bias and servo bias both sit at 1.56. But my B+ only came up to 158, still short of the designated 170. I'm wondering if the transistors took a beating by being installed backward.
I'm so close! :) :)
Atom
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Here is one Dan didn't include. I need often myself:
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi244.photobucket.com%2Falbums%2Fgg7%2FGrainger49%2FSmiles%2FSlapHead.gif&hash=e5c580c3cfdf525c26703ae0328aefb586b04de5)
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158v at the 6922 (or equiv) plate is a bit low, but the critical voltage is the grid to cathode voltage. That should be nominally the same 1.55v; if it falls below 1.3 volts or so then the triode grid may be sucking enough current to kill the bass.
Among the half dozen or so tubes that I measured some years ago, the 6DJ8 varieties were more prone to this than the 6922 types. I think it has to do with the metallurgy of the grid and cathode parts. Anyhow, that's why I built the circuit around the 6922.
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158v at the 6922 (or equiv) plate is a bit low......
Any thoughts, Paul, as to what might be the reason?
Atom
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I think he is saying it is tube dependent. Try a Soviet Military Surplus 6N23P (6Н23П, USSR Surplus, the -EV sounds better to me). They are inexpensive versus the high price spread and sound much better than the run of the mill 6922.
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158v at the 6922 (or equiv) plate is a bit low......
Any thoughts, Paul, as to what might be the reason?
Atom
If everything else is good, then a tube with more transconductance than average will require less plate to cathode voltage to obtain the same current.
Seduction operates the tube at the same operating point, nominally 3.8mA and 70v plate to cathode at 1.55v bias. Some tubes would exhibit low plate voltages, 55 or 60 v instead of the design value of 70v; this was with LED bias on the tube so you KNOW the bias is 1.55v. Eventually as the tube ages it will lose some transconductance and the plate voltage will rise.
That caveat above, "if everything else is good," means that the bias voltage as I described earlier must be adequate to prevent grid current.
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Thanks for everything, Paul. The Eros is on my bench getting a good inverse RIAA work-out. The 'scope display confirms what I'm hearing (and vice-versa). True Hi-Fi!!!
Atom