Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Foreplay III => Topic started by: Steve Reese on February 14, 2011, 04:52:04 AM
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Yesterday evening I finished installing the Extended parts into my Foreplay III. I did a visual check, and found a few mistakes on the A tube side. Did another once over, then put the tubes in and hooked up the power cable. Flipped the switch, and it started smoking on the B power supply side. It was on maybe 3 seconds before I turned it off. I had to look really hard on that power supply side before I found it to be the 220 UF 250V that's attached to 5U (striped) and 10U wasn't soldered completely on 5U. I resoldered, put the tubes back in, and put the cable on, then flipped the switch. No smoke, but diodes on B C4S light up on on the B side of the board. If I recall, the power shunt regulator board has no lights on the diodes. The A tube side C4S has all four diodes light up, although the A side of the board is much brighter than on the B side. I powered it off being afraid I would ruin more parts. Any suggestions will be greatly appreciated on where to look next.
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Hi Steve,
Now that you have got it to where it won't smoke when you fire it up, go over your resistance and voltage measurements again, and note here any readings that are off from the manual.
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Thanks Dan I will. Most likely will be tomorrow evening before I can get any readings taken.
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I'm just guessing, but if I'm looking down at the preamp with the wires exposed, I'm referring to the tube on my right as A. Please correct me if I'm wrong.
Here are the readings I got last night:
Terminal Voltage Resistance
H1 5.83 30.1
H2 12.81
H4 4
H5 12
1 (A) 88 (B) 91
2 (A) 0 (B) 0
3 (A) -0 (B) -0
4 (A) -0 (B) -0
5 (A) 0 (B) 0
6 (A) 70 (B) 90
7 (A) 187 (B) 221
8 (A) -0 (B) -0
9 (A) 199 (B) 223
10 (A) 190 (B) 218
11 0 468K
12 33 82K
13 -0
14 -0
15 4 0
16 0
17 0
18 -0
19 -0
20 -0
21 32 83K
22 5 30K
23 -0
24 0 0 ohm
25 0
26 0
27 0
28 -0
29 -0
30 -0
31 181 Infinity
32 187 150K
33 -0
34 -0
35 -0 474K
36 -0
37 -0
38 -0
39 0
40 -0
The PCB board B has no lights on section A, but B has lights.
Power Shunt Regulator PCB board section A has lights, but B only has it on the right diode.
The PCB board A has strong lights on A, but faint lights on B.
Thank you all who offer any advice.
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The readings from 1 to 10 look about right, so it would seem that the power supply parts are working OK. What you have labeled as the A side looks like some current is being drawn downstream of the power supply, that is pulling the numbers below spec. I think we actually label the tube sockets the other way around in the FPIII manual, i.e. as you look at the underside A is the far left one and B the far right one. Looks like the shunt regulator board is not working, so that is where I would suggest looking first for any missed solder joints or mis-wires. It might also be worthwhile to check the transistors. I think I must have posted how to do that a few hundred times, but I don't recall a specific repository for the directions. You want to measure resistance of each pair combination of the three leads on each transistor. If any combo reads really low like 100 ohms or less the transistor is toast.
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While Dan's away, I'll see if I can keep this moving... :^)
First question, do all the tubes light up, that is, are their heaters getting power? Especially the center tube which is the regulator (socket "R").
If the tube is working, then it is not regulating but it is getting power. The regulated voltages are on T21 and T32, and both should be 150v - you are getting 32 and 187v respectively. Can you measure the voltages on R1, R2, R3, R6, R7, and R8? That will tell us something about how it is not regulating. (The 32v at T21 is the reason H1 and H2 are off.) You may need to unscrew the A and B socket PC boards and move them to the side to access the R socket pins - we'll do something with those sockets eventually; I just want to focus on the regulators right now.
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Thanks Paul, here are the readings I get on the R socket:
R1 - 177
R2 - 0
R3 - 2
R4 - 11
R5 - 33
R6 - 0
R7 - 0
R8 - 0
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R4 and R5 should be soldered together - see the top of p.28 in the manual. These are the heater terminals, and this is the reason I asked of the tube was glowing. Presumably it is not, or at least only one half of it is glowing.
I see that R5 is at the T21 voltage, which should be connected to R6. I'd suggest carefully going over the connections to ALL the R-socket pins, but it is possible that these two errors could explain all the R-socket voltage anomalies.
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sorry... both A and B tubes are glowing, but the regulator doesn't show, but feels hot. I was in a hurry this morning before I had to leave on a beer run trip out of state.
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... I was in a hurry this morning before I had to leave on a beer run trip out of state.
Ah! A man with priorities!! I'm a wine man myself, but I can respect that :^)
No sweat; post again when you've checked out the suggested items.
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Okay, I removed the screws from the PCB board on the regulator tube, and in fact the readings on R4 & R5 are at 5. R6 is in fact attached to T21 and is reading of 33.
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OK, now we have new data and can try a different theory.
R1-R2-R3 is one regulator triode (plate-grid-cathode), and I see that the cathode is at 2 volts. I'll assume that is 2.0 volts, which as about as small a voltage as the 431 regulator chip can produce. The plate voltage, at 177, is well over the 150v. It is hard to make conclusions until we know what the "B" tube is doing - I think you said it shows no LEDs on the "A" end, so there is something wrong there. We'll get to that after we finish learning what we can from the regulator situation.
R6-R7-R8 is the other triode. It has 33v on the plate, and zero voltage on the grid and cathode. This regulator feeds the "A" signal tube, whose PC board has all four LEDs lit, so it may well be working correctly. In that case, the zero volts at the cathode (R8) indicates a wiring error or a shorted (blown) 431 regulator. There should be a black wire from R8 to the "K" pad on the B end of the board - check the locations and the solder joints. Also inspect the PC board for solder bridges around the 431 chip.
Now getting back to the "B" signal tube, check the voltages on the tube pins 1-2-3-6-7-8. This will tell us a lot about whether the C4S loads are working correctly on that tube, and once we know that we can finish diagnosing the regulator on that side.
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Here are the readings for tube B:
1 - 9
- 2 - 0
3 - 1
4 - 0
5 - 12
6 - 32
7 - 8
8 - 3
You didn't ask, but 9 - 5 to 6.
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Let me rephrase... the tube socket I'm referring to is on my left.... is that not Tube B? It's the one that the PCB board that only has lights on the B side of the board. What I'm calling A on my right side reads as follows
1 - 172
2 - 0
3 - 1
4 - 12
5 - 12
6 - 177
7 - 173
8 - 172
and 9 - 6. This is the side that all of the lights on the PCB board that works.
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OK, now I am confused! Please see Doc B's post in this thread where he repeats the tube identification from the manual, which is:
Looking at the chassis upside down, with the controls closest to you and the input/output jacks furthest away from you, the tube on the left is A, middle is R, right is B. (Also, all the PC boards have their "B" end closest to you, with the "A" end towards the jacks and power supplies.)
You can probably ignore anything I said about the signal tubes (A and B) after that post, since I was assuming you had corrected that mis-identification. I've been drawing conclusions from erroneous data after that post.
Bottom line, the regulators are not working correctly, and the "tube on the right" that has the high voltages and the lights that work, is also not functioning correctly. I can't tell about the other tube until its regulator is working and supplying voltage to it.
Right now I have a terrible cold and low-grade fever, and I'm sleeping about 15 hours a day. This has become too complex for me to deal with effectively. I'll take another shot at it in a couple days when I feel more competent. Meanwhile, would you summarize the tube voltages with the correct designations, and if your meter allows it measure the smaller voltages to 2 or 3 places? This is particularly important for the cathode voltages (pins 3 and 8).
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I apologize Paul for the confusion. The colds/sinus infections have went through all of us here at my house. Here are the readings from Tube A:
1 - 9
2 - 0
3 - 1
4 - 0
5 - 12
6 - 32
7 - 8
8 - 3
You didn't ask, but 9 - 5 to 6.
For Tube B, the readings are:
1 - 172
2 - 0
3 - 1
4 - 12
5 - 12
6 - 177
7 - 173
8 - 172
and 9 - 6. This is the side that all of the lights on the PCB board that works.
I hope you feel better soon.
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Would you like for me to get any voltages from the boards?
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!^@%#$*$&^
Sorry, I just wrote a really long and detailed post, and failed to check whether it posted. It didn't because you were posting at the same time! OK, guess I feel better but I'm not fully functional yet.
I'm not going to repeat the analysis. Suffice it to say that I think both regulator C4S's are blown, and at least on of them on the B tube. The regulator socket has a short from pin 6 to ground, which may or may not be on the board.
Usually this means it will be much faster and more reliable to simply replace all three boards with new ones, using new components, and being very careful to get the right wires to the right tube pins. Take it extra slow and easy this time, because once you have made any wiring errors, they become very difficult to see afterwards. Believe me, this is the voice of (bitter) experience talking! :^) If you can get another set of eyes to check your work, do it.
Contact Eileen or Doc B, they'll fix ya up.
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Thanks Paul... that's how I was leaning towards deciding on. I do hope you're feeling better, and thank you very much for your time and effort.
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All resistances test good
H1 - 39 H2 - 46 H4 - 39(?) should be 0 H5 - 46(?) should be 0
1 - 91 should be -
2 - 0
3 - 0
4 - 0
5 - 0
6 - 81 should be 0
7 - 221
8 - 0
9 - 217
10 - 214
11 - 0
12 - 219 should be 150
13 - 0
14 - 0
15 - 76
16 - 0
17 - 0
18 - -
19 - 0
20
21 - 220 should be 150
22 - 39
23 - -
24 - 0
25 - -
26 - 0
27 - 0
28 - -
29 - 0
30 - 0
31 - 78
32 - 213 should be 150
33 - -
34 - -
35 - 0
36 - 0
37 - 0
38 - -
39 - 0
40 - 0
what worries me are terminals terminals 1, 6, 12, 21, and 32. The lights on the regulator are very dim. Is that normal? Should I go ahead and hook it back up in my system? Much thanks to all who may reply back.
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The regulators are not regulating; otherwise it looks good.
Do the heaters on the regulator tube (center tube) glow? You said something about the "lights" but I don't know whether you meant the heaters inside the tube, or the LEDs on the regulator board. If the tube filaments are not getting power, then the regulators won't regulate.
If they are getting heater power, try swapping with one of the signal tubes, A or B. That is just to confirm that it's not a bad tube. Unlikely, but best to be sure about assumptions.
If the tube is good and is getting heater power, then it must not be connected to the regulator board correctly, or there is a problem on the board. If the resistances at 21 and 32 are correct (83K and 150K respectively) then the voltage divider string on the board (R3 and R4) are correctly connected to the circuit. That leaves two possibilities I can see - tube pins 3 and 8 are not connected to the board, or the TL431 chip is inserted backwards.
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Paul, I have removed the regulator board and examined every solder connection. The chips are inserted correctly. On the board both R3 and R4 are connected correctly. I rechecked their resistance, and R3 is what it's supposed to be at 2.49K, but R4 on both sides A and B is off for some reason. Their color code is correct, and I know that they were the correct resistance before I installed them. But on the B side R4 reads at 82.5K and on A is reads 115.3K. Another strange reading on both pin R3 and R8 reads 1 volt instead of 0. What I meant about the lights, is that the diodes glow is really low. On the tube compared to the other tubes, there is no glow at the bottom of the tube. And the tube is cool to the touch.
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No glow, and a cool tube, suggests that the heater is not getting power. Since there are two heaters in parallel, it is unlikely that they are both broken, but swapping in another tube would test for that.
The tube should have pins 4 and 5 connected together, and wired to the 6.3vDC heater supply that powers the other tubes as well. The other side of the heater supply goes to pin 9. Ypou should be able to measure 6.3vDC between tube socket pins 9 and 4-5, on each of the three tubes. If you don't find a bad or missing connection that way, it is always possible that the socket itself is not making good contact with the tube pins. Others have posted ways to deal with that problem; and have more experience with it than I do - hopefully if you determine that is the problem, one of them will contribute! (Grainger?... :^)
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Steve,
If it does indeed turn out to be the socket I first go through the insert, remove, insert, remove scenario. Try it 6 times first. Not only does it work 50% of the time it sounds dirty too.
If that fails turn it off, wait a couple of minutes and flip it over. Then I use a sewing needle to coax the tube socket receptacle more closed for the offending pins. Do it gently and the socket will really grab the tube pins. Do it roughly and you might end up with a broken ceramic socket. Just keep your eye on the metal inside the socket.
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After reading Paul's last post yesterday afternoon, I immediately began searching over in Audio Asylum to try and find out how to "tighten"the tube sockets. I went and found a saftey pin and began trying to push the metal pieces together. Socket 6 through 9 were no trouble, as was socket 1 and 2. But 3 through 5 was much harder for some reason, and I was just about ready to give up after powering up, taking readings, and seeing no lights on the regulator board. So this morning I read Grainger's suggestion about using a sewing needle, and after asking my patient wife where they were, I went back at it. The first time I didn't see a change, so I repeat inserting/removing the tube at least 8 times. Last week I had tried different tubes I have around, but this time I bought out an Ameperex industrial looking 12AU7 with weird shaped grid plates. Sanded the pins, and once again, I inserted/removed the tube... No luck. I took the sewing needle and began messing with all the sockets, but paying more attention to socket 3 through 5. I turn it on... and no lights. I was taking reading on all of the pins on each tube, when I look over at the regulator board, and man they were shinning bright!! They were brighter than either A or B side. I took the voltage readings, and they were spot on. I let it stay on for about an hour just to make sure it wasn't going to short out or anything.
After that, I took it back upstairs and hooked it back up in the system. My first impression was that it sounded more precise. As what has been my source CD throughout the years, Frank Zappa's One Size Fits All, the highhat and cymbals reminded me how Klipsch Hersheys sound... with air. That's how my Straight 8's sounded. On the third song, Sofa #1, a bass Moog drops maybe down to30 some hertz. The bass was tight and precise along with the Dan and Paul Sub that they graciously gave us all the plans to try. Now mind you, our 5 year old daughter stayed home with me as my wife ran some errands, so to say I was distracted some is putting it mild. So after Zappa was done, I put in one of her favorite CD's They Might Be Giants -- Here Comes Science. I went into the kitchen to do some stuff... then she'd run in and say 'Did you hear that (now imagine a 5 yr old making an instrument sound). She's only heard it in both of our cars so..... She had a good time... plus I also allowed her to make some basic solder connections with some spare wirel...
I want to thank Dan who began trying to help me, but I can't thank Paul enough. You two have been blessed with patients of a saint. And Grainger, thank you, I always love reading your insights... the sewing needle... can't wait to tell this over some pints later with the guys... And now the addition is back.... with a vengence...
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This one has been a long road getting there, I'm so happy you were able to fix it yourself - feels so much better than throwing in the towel and hiring someone. Congratulations!
Also I'm happy it got resolved before I left town, I just hate to leave things like this unresolved. :^)
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I'm always happy to help and amuse.