Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Foreplay III => Topic started by: Frank Breech on August 29, 2012, 01:08:10 PM
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Hi,
I had my newly built FPIII running for a couple of days and was really enjoying it. I had some noisiness on the right channel. I thought it was in the right SW pot, but then I realized it was whenever the chassis got jostled at all, especially between the SW and the right 12AU7 socket. Then, I noticed that moving the tube or at least the tube socket on the right channel made this noise much much worse. In wiggling the tube around, eventually the sound went away. The LEDs on both 12AU7 sockets do not light up. So, just re-checked resistances. All were ok.
Then just re-checked voltages. The two voltages that are off are Terminal 15 and Terminal 31. Both should be around 75VDC according to the manual. They are now both at ZERO.
Please let me know how to proceed. I feel like I need two new 2.2uF 250V capacitors. All help is appreciated as I'm new to this.
Incidentally, I found a bad solder connection at 12AU7 socket terminal 6, which was probably the cause of my original problem.
Thanks in advance
Mike
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Start by going back and reheating every solder joint, and then trying the voltage check again
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Ok, will do. What do those two bad reading terminals have in common? Is there a single joint or series I can rewet and /or check first?
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Both those terminals are attached to the right and left Cathode Follower Cathodes. With zero volts there the CF stage is not working. Both 12AU7 tube pins 8 should read 22.1k ohms to ground.
The associated plates are tube pins 6 on the same tubes. Are those the right voltage?
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Grainger,
I will check the 12AU7 from pin 8 to ground.
To test the voltage on tube pins 6, where/how should I measure? What should the correct voltage be?
I will try to test this tomorrow. Also, will go for reheating every solder connection but I want to try to understand this thing at least a little bit, so thanks for these troubleshooting tips.
I'll post my results as soon as I can get to do the work.
Mike
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Mike, I was going to suggest looking at and reheating the joints starting around that socket. For some reason that other thread got locked. Glad you re-posted. Im sure Grainger and Doc have you on the right track. They are much smarter guys than myself when it comes to this stuff.
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Mike,
I keep forgetting, the FP III takes voltage readings from the terminals rather than the tube pins. It is safer as close together as the tube pins are. Read to ground, that is the power supply common. The two plates should be connected to the OD3 regulated voltage, that is terminal 21. The plates are attached to terminals 12 and 31. All three should be 150V or there about.
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Grainger,
Ok, got it, thanks for the clarification.
Those readings are fine, that is: in line with what the directions call for. I had only listed my problem voltages. (also, you said "terminal 31" in your last message but I think it was a typo, should be terminal 32, right? Please confirm.
To be sure:
Term: My voltage reading:
12 146VDC
32 146VDC
21 146VDC
Also, to be sure:
both 12AU7 tube pins 8 do read 22.2Kohms to ground.
All resistances checked out, then all voltages checked out except to terminals 15 & 31 (as in the original post). Need to get a few minutes free to reheat all connections. I 'll you know what happens.
Laudanum,
Thanks for the support. Don't be so hard on yourself ;)
-Mike
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Right, 32. See, all those are good. If the cathodes, terminals 15 and 31, are functioning you get some voltage there. First check the resistance from terminals 15 and 31, it should be about 22.1k.
If it reads right go back and touch all the solder joints within the two cathode circuits. Touch up both 12AU7 tube pins 8, terminals 15, 19, 31 and 39. The two red wires and two resistors comprise the cathode circuits.
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Hi, Just did all of this that you mentioned above. Must have been doing it while you were writing. I retouched all solder connections from terminals:
-11 thru 40 (both H & L)
-All 12AU7 Pins that are connected. (except i'm not sure how well I got the center pin, it was a tight fit with my iron tip)
-All Sweetest Whispers Channel A (right channel) since this is where I thought I was hearing the noise originally.
Then Rechecked voltage at 15 & 31, but still getting 0VDC there. Also, the LEDs on the 12AU7 sockets do not light when I power up.
Mike
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Try measuring the voltage at pin 1 and pin 6 of each of the 12AU7 sockets
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So both channels are dead. Booger! If it were one you could swap tubes.
You have a properly regulated voltage at the plates, well at the terminals that feed the plates. Let's try this another way.
Put one meter lead on the Octal socket pin 5. That is the output voltage of the OD3. Measure resistance to tube pins A6 and B6. Each of these measurements should be 22.1k ohms. This would say that the ~150V of the OD3 is getting to the tube plate.
You verified that the other 2 - 22.1k resistors were attached to the respective cathodes and ground. So that sounds good. Checking the plates back to the source where you do have the right voltage checks the other part of the circuit.
And now you tell me that the HLMP 6000s are not lighting. So nothing is conducting. Hmmmmmm.
Stick with us, we can figure it out.
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Doc, Measured Voltage at the 12AU7 pins you suggested:
1A 147vdc
6A 147vdc
1B 147vdc
6B 147vdc
Grainger, Measured the resistances you suggested:
Octal Socket 5 to A6 0Ohms
Octal Socket 5 to B6 0Ohms
however Octal Socket 5 to A7 and B7 are 22.2K (not sure if this info is helpful)
Also, those LEDs have not been lighting since the very beginning of my trouble. When I first lost sound. I wiggled the right tube (socket B) and the LED went on and off. After power cycling once, the LEDs were dim and audio was VERY LOW. Power cycled a second time and neither LED came on and, no sound.
-Mike
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. . . Grainger, Measured the resistances you suggested:
Octal Socket 5 to A6 0Ohms
Octal Socket 5 to B6 0Ohms
however Octal Socket 5 to A7 and B7 are 22.2K
. . .
My mistake when I said A6/B6 I should have said A1/B1. A7/B7 is almost like A6/B6 so your 22.2k is good. Matter of fact spot on to what you should read. With no LEDs lighting in the VA side and the cathodes at ground, passing no current, neither side of the tube is conducting.
I'm convinced it is something we have overlooked, simple but catastrophic to both sides of the tubes.
Something is wrong here and it is both channels and both triodes for each channel.
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Is it possible to ring out my tubes with the mm?
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The tubes should be fine. They should be new EH tubes. The only connection is between tube pins 4, 5 & 9. That is the heaters. All others are isolated by the vacuum in the tube.
Are you asking about ringing out the tube sockets?
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I'm sorry that I don't understand your last question, Mike.
If you have 146 V on pins 1 and 6 the high voltage is getting from the high voltage supply to the tubes. So either the LEDs are shot - not that likely - or more likely the 12AU7 heaters are not getting the correct voltage. Try measuring the heater supply voltage at the 12AU7 socket pins. That would be using the black test lead on pin 9 and the red test lead on either pin 4 or 5, as they are connected together. You should see about 6.0 to 6.3VDC.
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And Dan came up with something very simple that would keep both triodes in each 12AU7 from working.
Plus, if they get warm that indicates some voltage on the heaters. Not necessarily the right voltage but some.
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Hi, Guys,
Thanks for the notes.
I will try measuring the heater supply voltage as you describe.
I will get back to you tommorrow morning. I have the unit in my office. Actually, my boss is on vacation tomorrow so I can devote as much time as need be to this. I'd like to listen to Tom Waits's Heart of Saturday Night this weekend, if possible.
RE the LEDs: While I'm not sure how to tell if they have gone south, I can tell you this ... When I use the continuity tester through them, they do indeed light up.
RE my question about "ringing out the tubes with my multimeter": Maybe that question just plain doesn't make sense. I was thinking maybe the heater filaments (is that the right word?) were blown or something, kind of like a lightbulb, and I could test that with continuity or resistance meter from pin to pin. Is something like this possible?
Thansk again
Mike
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Mike,
You should pull a tube and put your meter between tube pins 4 and 5. Whatever you get there you should read about half that between 4 and 9 and the other half between 5 and 9.
Give that a try. I bet they are fine.
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Yeah, if the LEDs light up with the meter they are OK. It's very unlikely that the heater filaments blew. I suspect a bad solder joint somewhere in the heater supply wiring or possibly a blown diode in the heater power supply. Check the voltage at the tube sockets. If there is not about 6VDC from 4/5 to 9 then start your way back from the sockets to the heater power supply and see if you can find an open connection. Then check across the pins that the blue 10,000 uF capacitor is soldered to pins H1 ( black test lead) and H2 (red test lead) and see if you get about 6VDC there. If not, it could be a bad rectifier diode. Let us know how that goes and if necessary we will investigate the diodes.
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Ok, great. This will be good to get me started tomorrow morning. The only thing I'm not so sure about is when you (Doc) say: "start your way back from the sockets to the heater power supply and see if you can find an open connection"
Does this mean keep one test lead on tube socket 9 and test backwards? If so,(or even if not), I'm not sure which points to touch when working my way backwards. I don't want to short something out. Can you please confirm which terminals trace the route back along the heater supply - or otherwise set me straight?
thanks
Mike
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Follow the wire - it's shielded twisted pair - visually. IT goes from teh A socket to the B socket, so test the voltage B9 to B4/5. From their it goes to the heater supply; check the voltage H1 to H2.
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Ok. Sounds simple. Thanks for the confirmation.
Also want to be sure, would I be tracing this path from tube socket B9? That is, should one lead stay on 9, then as I back track, I'll see where the voltage stops coming through?
Forgive me & thank you
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You will read from tube pins 4/5 to 9 on both tube sockets. Moving the leads from socket to socket. Then move the leads back to the power supply at the back of the chassis where the STP (Shielded Twisted Pair) comes from. If you get the meter leads swapped nothing bad will happen you just get negative voltage read on the meter.
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Ok, fellas...
Socket B:
pin 9 - 4/5 1.8vdc
Socket A:
pin 9 - 4/5 1.8vdc
Heater Supply:
H1 - H2 Zero vdc
I feel like this doesn't even make sense. Is the heater supply upstream of the tubes? If it has zero vdc, how can the tube heaters have anything? I did go back and double check these readings.
What do you think? Is there music in my future this weekend?
Mike
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Bingo ! ! !
We have found the problem.
Measure between the transformer terminals 4 and 5. It should be somewhere around 6.3V AC.
Verify that the black stripe on the 10,000uF cap is toward the RCA jacks.
Go to page 28/29 in the manual and verify that the diodes are in the right direction.
Verify that the wires connecting transformer terminals 4 and 5 to the terminal strip H1 H2 make good contact.
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Measure between the transformer terminals 4 and 5. It should be somewhere around 6.3V AC.
6.1 VAC
Verify that the black stripe on the 10,000uF cap is toward the RCA jacks.
This is NOT toward the RCA jacks. However, the lead closest to the black stripe is definitely connected to terminal H1.
Go to page 28/29 in the manual and verify that the diodes are in the right direction.
Check.
Verify that the wires connecting transformer terminals 4 and 5 to the terminal strip H1 H2 make good contact.
Check, I rewet these.
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If you have 6.3V AC at the power transformer and nothing after the rectifiers its probably a bad solder joint around the rectifier bridge, or equally likely you have a blown rectifier. With the amp unplugged take a resistance reading across each 1N5820 rectifier with the red on the striped end and the black on the non striped end and record the numbers. Then do the same with black on stripe, red on non striped.
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Red on Striped Side of Rectifier: Black on Striped Side of Recitfier:
#1 408 ohms ...........................................60 ohms
#2 380 ohms............................................60 ohms
#3 470 ohms............................................60 ohms
#4 450 ohms............................................60 ohms
I should mention that while the 60 ohms readings are very steady the other readings are fairly variable. They settled to each of the above listed #s, but I did the readings a few times and often got different results. These readings are the most common ones I got.
Also, My MM instructinos say that using the continuity setting, I can perform a diode test. I tried this and can give you those numbers if it would help. I did not hear the continuity beep when testing the rectifiers in either direction.
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OK clip the black lead to H1. Now take a VDC reading with the red lead at each end of the white resistor, H2 and H5.
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H1 to H2 --
1.6VDC (see next post)
H1 to H5 -- 1.8VDC (see next post)
Interesting. Earlier today, when I did H1(black lead) to H2 (red lead) I got a reading of zero. see post Today at 05:20:20 AM Posted by: Frank Breech
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Ok, found a loose connection at the heater.
My I am editing the above readings, the new readings are:
H1 to H2 6.75 VDC
H1 to H5 6.75 VDC
still no light at the LEDs at the tube sockets.
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So you must now go back and see if that voltage is actually at the tube sockets too - 4/5 and 9.
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The voltage is at the tube sockets. The LEDs are lit. The 12Au7s are lit.
I feel that everything should be ok now.
That bad solder at H1 must have been the culprit.
I will bring the unit home and post the result.
Thank you for all the guidance.
Mike
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Now you see why my first post in a troubleshooting thread is most often -
http://www.bottlehead.com/smf/index.php/topic,3284.msg28329.html#msg28329 (http://www.bottlehead.com/smf/index.php/topic,3284.msg28329.html#msg28329) ;)
Carefully reheating every solder joint and visually inspecting it with a magnifier to make sure everything is properly coated with solder and secure in the joint is the best way to start to sort out a "not working" issue, particularly one where the circuit was working initially. It can save a lot of other testing and probing.
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Please refer anyone to me who might doubt this.
I will let you know what happens this evening when I get it hooked up. I'm hoping I'm not back to square one with the noisy right channel. I did rewet all sweetest whispers connections and cleaned the tube sockets with Grainger's method (dental brush and contact cleaner).
I might put on Tom Waits's Heart of Saturday Night on a Friday. Unheard of, but possible.
I did also enjoy the troubleshooting as it got me realizing what was what better that before - even if just a little bit.
Thanks Again
Mike
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I should have described the black stripe on the capacitor differently. I was looking at the first picture on page 28 of the manual. I see now that the input RCA jacks are to the right, the output RCA jacks are to the left. The black stripe should be to the left.
Two things you have measured point to the diode string. You got 0V H1-H2, which is where the cap is, and you got 6.1V AC on the transformer. The diodes are all that connect those two points. Of course the diodes are what make DC out of AC and smoothing it gives you a little more than the RMS AC value.
You are right on top of it now. This has got to be it.
Edit: I now see all the back and fourth that I missed where you and Dan figured out the missing/loose connection at H1.
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Grainger,
Thanks for the follow-up.
I'm at home, the amp is sounding very nice. No more noise on the right channel when touching that side of the chassis. I'm having just one issue (which might even be a hold over, partly, from my original issue):
one channel is softer than the other. In this case it follows the tube. Whichever socket I put the suspect tube into, that channel is about 2 sweetest whispers clicks below the other side.
Any ideas?
I did not check the pins of my 12AU7 tubes as you described to me in an earlier post. I can do that. I'm burnt out for tonight ... just glad to be listening, even with the SW pots at different settings.
Thanks Again,
Mike
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It could be fatigue, but I 'think' the channels are evening out, level-wise. Is is possible that it could take a while for one channel to get warmed up or something to output the same as the other channel?
They are still a bit far off, but better than before. When I attenuate each all the way, but the CD player is still going, I can hear the music through one channel (the louder one) a bit, but cannot hear it at all through the other (softer) channel.
Mike
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It could be that the cathode is still forming - a search on this site will turn up several posts. We seem to have seen this more than a few times, though I don't see much mention of it on other sites. It can take 100 hours or so if that's the case.
"All the way off" means the switch has grounded the output to the tube. If there is a little resistance in the wire, switch contact, or solder joints, then there will be a little leakage. This is the wire from terminal 1 of the Whispers to terminal 16 or 40. It won't affect the balance on the higher switch positions to any measurable degree, so you can ignore it unless it either gets worse or just bothers you.
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Mike, if you swap tubes around and it follows the tube, it is the tube. But definitely follow Pauls advice and give the tubes some run time. That may solve it. Also ... here comes my standard advice ... get yourself a spare or two of each tube. In the case of FPIII, two of the same type 12AU7's and a spare OD3. The OD3's are really inexpensive, literally under 10 dollars for new (old stock) tubes like Hytron and RCA brand. And I paid 3 or 4 dollars for a couple new old stock spares. The 12AU7's are relatively inexpensive for new production tubes (like the EH included with the kit), maybe 15 dollars or less per tube. But you can even find some of the New old stock vintage tubes for less than that. The more highly prized 12AU7's are more but the point is having a couple of spares to troubleshoot or get you up and running should a tube go south. So grab some spares.
ps. If shopping for new old stock tubes, look around and shop wisely (price wise).
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I agree with all the above. As I read the problem I had the same thoughts.
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Thanks, guys. I'll give these tubes some time, get a set of spares, and let you know if is any trouble. I'll bee in touch soon most likely. Going to get started on my seduction.
Thanks a lot
Mike
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Hi Guys,
UPDATE: my FPIII channels are now evened out -- one is not louder than the other any longer and it has been stable for a few weeks.
Thanks for all help.
Talk to you later