Bottlehead Forum
Bottlehead Kits => Eros Phono => Topic started by: Tom228 on July 18, 2013, 03:51:10 PM
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Hello all.
Slowly getting my new Eros put together and I think I have a voltage issue.
I put the power supply in and the output voltages are where one would expect. Checking at the 5w resistor, I measured 362v and at the 6v output it was 6.3v.
Got the shunt regulator installed and measured the output voltages (forgive me, I don't have the manual right handy) off of D1 and D6?? at 260v where the manual says it should be 225v. Is that too high? The tube glowed right nice and purdy. Put off a lot of heat, too.
Thanks in advance for your help and time.
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Yeah, that's not good. It should be 225 +/- 1 or 2% - it is set by 1% resistors. Best give the tube pin voltages (except 4/5/9, they are the heater which apparently is working fine) - also IA, OA, IB, OB on the reg board. Are all four LEDs lit?
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Where would I place the neg lead of my meter when testing the socket voltages?
All 4 LEDs are lit. One side was slightly dimmer than the other.
The voltages coming off the power supply are fine, according to the manual. I looked at page 13 and the resistors listed there are in place on my board. I have verified that the shunt regulator board is in the proper orientation with bA, OB/IB closest to the power supply.
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Here are some voltages:
5w resistor - 276v (this was up around 362 when I did the voltage check prior to installing the shunt regulator)
6.3v output - 6.28v
Red lead off of D6 - 272v
Red lead off of D1 - 257v
d7 - 0v
OA - 270v
IA - 273v
OB - 262v
IB - 274v
I'm not very comfortable with getting into the other pins on the socket with the system on.
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What are your Kreg voltages?
Also, do you have the 12BH7 installed?
-PB
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Hi Caucasian Blackplate - yes, it is glowing real purdy like and is quite warm. I can feel the heat coming off of it from 4-6" away.
kreg closest to the power supply board - 1.86v
kreg furthest away from the power supply board - 1.85v
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OK, that's useful. The low kreg voltages indicate the tube is trying like crazy to sink enough current to pull the voltage down, but the OA and OB voltages indicate it's not succeeding.
Two possibilities are immediately apparent - either the C4S is generating too much current (are the R1 values correct?) or the C4S output OA and OB are not connected to the tube plates (pins 1 and 6). The latter is why the plate voltages are helpful. You may need to unbolt the PC board and push it out of the way to get those measurements.
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Hi Paul.
On the A side R1 is 37.7 and on the B side R1 is 37.5.
Does the orientation of the capacitors (104k) on Cc matter? The text on mine is facing inward. Whereas, the pictures in the manual have the text facing outwards.
I have OB going to pin 1 and OA going to pin 6 and have verified that they are indeed connected. The board is oriented with A on the left and B on the right.
Pin 1: 260v
Pin 2: 0v
Pin 3: 1.87v
Pin 4: 6.28v
Pin 5: 6.28v
Pin 6: 272v
Pin 7: 0v
Pin 8: 1.86v
Pin 9: 0v
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Additionally, if the black wires going to Kreg got switched, this kind of problem would present itself.
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The large amount of heat from the 12BH7 suggests it is indeed conducting a lot of current, which is consistent with the measured voltages. If the R1 is correct and the LEDs are lit (meaning R2A and R2B are correct) the I worry the transistors (the large ones, MJE5731A) may be reversed, or have a solder bridge at their connections.
Here's a test, if you can't find anything along the lines either of us Pauls have suggested: Unsolder the black wire at D3, leaving it connected to kreg on the board. Put your meter (use clipleads!) between D3 and the black wire, and set it for 200mADC to measure the actual current. If it reads 23.5mA then the C4S is good; if it reads a lot more then the C4S is delivering way too much current, and something on the board is either mis-wired, fried, or has a bad solder joint. (Or, as is always possible, there is something else I have not thought of that's gone wrong!) This one is a puzzler.
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I'll give that a try, Paul.
I've removed the board and inspected it real-close-like to verify there's no solder bridges. The 2 transistors are facing the proper way, according to the document (that is, their metal sections are pointing towards each other, looking at the other components on the board).
I checked up the solder joints on both R1's and reseated the 104k's to match the orientation shown in the build guide.
Someone remind me to ask for a solder sucker for Christmas. This wick sucks! :*)
I will try to get that current measurement ASAP.
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Paul - Kreg->D3 = 22mA.
Got it put back together:
d1 - 261v
d6 - 275v
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Hi all.
What do I do now?
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I would recommend posting some quick photos of the PC board and socket wiring, so we can look it over.
-PB
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Here's some I've taken as the build has progressed. I'll get a couple more tonight (no FB login is required):
https://sphotos-a.xx.fbcdn.net/hphotos-prn1/1015018_10201814471342721_1260350501_o.jpg
https://fbcdn-sphotos-e-a.akamaihd.net/hphotos-ak-frc1/1026000_10201597415636464_103837924_o.jpg
https://sphotos-b.xx.fbcdn.net/hphotos-ash4/1008730_10201597352074875_316818426_o.jpg
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Here's the images from tonight:
http://imgur.com/a/QyjGR
Nice shiny high-res ones :)
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I'm not seeing the errors that would cause this.
Can you:
1. Meausre the DC voltage on both sides of the 270 Ohm resistor?
2. Verify that you have MJE5731A transistors on the board (not TIP50's or anything else)
We'll get this sorted out.
-PB
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Hi Caucasian Blackplate.
Thank you for all of your help with this. While I'm pretty good at following directions and putting stuff together, I'm not great at troubleshooting. So, all of the help is most appreciated.
When I measure the DC voltage on teh 270 Ohm resister - is that the big 5w one on the power supply? Do I leave the - probe on the back resistor both times? Do you want that with or without the shunt regulator attached?
I'll post a picture of the transistors tonight.
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With the regulator attached, place the black probe in the ground post at the front of the chassis plate, then use the red probe to measure the voltage on each side of the 270 Ohm resistor.
-PB
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I've got MJE5731AG (AFB43) transistors on the shunt regulator.
Off to re-attach it.
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Ok:
2 -270k resistors:
Resistor closest to the top of the power supply board:
Bottom pin (red band): 142v
Top pin (gold band): -0.001v
Resistor closest to the bottom of the power supply board:
Bottom pin (red band): 286v
Top pin (gold band): 142v
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Sorry, I may not have been clear enough, I'm interested in the voltages on either side of the single green 270 Ohm resistor.
-PB
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Right side - 280v
Left side - 292v
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Hi all.
Can I keep moving along with assembly of my preamp? I'm to the point of wiring up the 3 tube sockets and the stand-offs. Or should I wait until we get this figured out?
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Tom,
I haven't dug into this since you were getting responses. Bottlehead hosted a meet yesterday, so your responders were busy. I'm headed to Church. If you don't have a response when I get home I will open the manual and see what I think.
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Tom,
I'm home. I don't know how we got to looking at the 270 ohm resistor so bear with me as I jump from the instructions to the schematic and think out loud. I see now that PB (Paul Burkeland, AKA Caucasian Blackplate) is looking to see how much current is being drawn through the power supply. I=V/R so he can get a handle on what the circuit is drawing (current).
I think there are three things to verify. First you need a good ground for the power supply board. You tested it on the top of page 45 in the manual. Or at least that is where it is in my manual.
It comes off the board at the top of page 52 on a pad labeled "375V DC -". It is the first instruction on that page. If you measure resistance from this solder pad to the chassis plate it should be less than an ohm.
The 270 ohm 5W resistor is part of the power supply filter. It is between the first and second capacitors in the high voltage DC supply. If the tubes are in, the circuit should be regulating, as Paul Joppa posted. When this happens there is a fixed voltage across this big white resistor. The output of the power supply, before regulation should be about 275V (within 15%). And 225 with a close tolerance after being regulated.
You said, "5w resistor - 276v (this was up around 362 when I did the voltage check prior to installing the shunt regulator)" This is good. The first measurement had no current being drawn, 276V with the regulator hooked up is 1 volt higher than I stated above.
BTW Cc caps don't have an orientation.
When Paul or Paul post back they can give you better guidance as whether the circuit is pulling the right current.
As PB said, we will get you through this and you won't believe the sound you will have created!
Hang in there.
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Hi Grainger49.
Thanks for the tips. While I am jonesin' to get this thing done and off of the bench (read: kitchen dinner table), I don't yet have a TT or a amp. So, it's not like I need to be in a rush to get it done (contrary to a couple of TT having friends who are anxious to try this thing out).
I measured the resistance as you requested. Red measure lead on the negative 375v pad and the black measure lead to the chassis plate and I got 0.2 ohms.
The voltage on the +375 lead has come up a bit during the course of testing and moving stuff around. When I first turned the power supply on, it was indeed showing 362v. I tested it again just prior to putting the shunt regulator back on the board and the voltage had come up to a closer 371v w/o the shunt regulator attached.
My 5w 270 ohm resistor is green and round. Voltage on its pins are (left): 292v (right): 280v with the shunt regulator attached.
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My 5w 270 ohm resistor is green and round. Voltage on its pins are (left): 292v (right): 280v with the shunt regulator attached.
It's not exactly what I predict, but pretty close - close enough to draw the following conclusion:
* The current through the shunt regulator tube is no more than the C4S target
We already know the following:
* The bias on the shunt reg tube (terminal "kreg") is as low as the 431 can make it.
* The bias voltage for a new tube should be at least 7 volts.
* The plate voltage on the reg tube is closer to the supply voltage than to the target 225v regulated
* The shunt reg tube is getting adequate filament power (the heater glows visibly, the tube gets hot, and the measured 6.3 volts is correct)
Based on these observations, it sounds like the 12BH7 tube is just not conducting enough. Contact Eileen on Monday and get a replacement tube - mention this thread and someone should test the replacement before shipping it.
It is possible the cathode was poorly formed at the factory and it will eventually conduct better - typically 50 to 200 hours of running will do that. However, the tube should not be run for any extended time without the rest of the circuit - it will be get too hot - so I cannot recommend doing this in the Eros circuit.
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Thanks Paul! I will give her a call tomorrow.
Is there any way I can test the tube? Or do you need special gear for that?
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Good news everyone!
The new tube came in. Installed it and checked D1 and D6 and WAMMO BLAMMO! 223v! :)
Soldered D1 and D6 into their homes, completed the circuit checks and then the big moment came. "Please don't catch fire, please don't catch fire" I chanted as I plugged the cord into the wall.
No fire! And all of the voltage checks came out in spec!!!
I could not see the two X79 tubes glowing. But I know they had voltage. Is that normal? The center tube was glowing. May have to wait until it gets dark to see the glow.
Sadly, I have nothing to hook the preamp up too at the moment. :(
I picked a ProJect Experience 2 from the Needle Doctor. It should be here later this week as should the new AVR (Denon 4520). Hopefully late this next weekend I'll be enjoying it all! Thanks very much to everyone for their help!!