Bottlehead Forum
Bottlehead Kits => BeePre => Topic started by: ScottAstroNut on July 30, 2020, 02:23:56 AM
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Hi All! I just finished my BeePre build, an have no sound at all coming from the right channel. The left channel seems to be working just fine.
Here's what I've done so far:
1) Checked all connections (interconnects, power, etc,) No issues found.
2) Swapped tubes. No effect. Right channel still dead but left channel works.
3) Checked tube glow. All tubes glow fine.
4) Checked LED's. All light.
5) Inspected all wiring. Found one miswire: I had connected the 10 microfarad 250V capacitor to terminal 50 instead of 51. Fixed that. Found one iffy solder joint, resoldered that. For good measure I resoldered the center output for the right channel.
6) Did resistance tests several times. The only ones out of bounds were:
A4 at 3.0 ohms
B1 at 4.6 ohms
B4 at 5.4 ohms
7) Did voltage tests several times. The only ones out of bounds were:
Terminal 17 at 88.4V
B2 at 88.2V
At this point I am thoroughly flummoxed. Help would be appreciated.
Thanks!
Scott Burgess
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Hey Scott,
I'm no expert, but I had the same problem when I first built my BeePre - I had miswired the A B C D terminals on the selector switch. Have you tried all three pairs of inputs on the BeePre? If that doesn't make a difference, I'd double check all the red and black wiring at the input selector switch and the balance and volume pots. I'd also test whether signal is getting to the grid of the right 300B. With amp unplugged and cold, I'd connect one test probe to A3, set the input selector switch to input 1, set the meter for continuity, and connect/touch the other probe to the center pin of red/right rca input 1. If the meter doesn't beep, I'd try to figure out where the break in connection is -- e.g., leaving one probe connected to the rca center pin, remove the other probe from A3 and put it on D (red) of the selector switch, and then on each of the lugs on the balance and volume pots to which a red wire connects.
If the red signal wiring is all good, I repeat the same continuity test for the signal ground, starting with one probe on terminal 8 and the other on the ground/-ve tab of red rca input 1.
Don;t know wither the above will help, but it's worth a shot.
cheers, Derek
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Thanks Derek,
I will give your suggestions a try.
Scott
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Terminal 17 at 88.4V
B2 at 88.2V
Do these move if you swap the 300Bs?
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Hi Paul,
I will give that a try and see.
Thanks,
Scott
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OK. I did more poking around. In checking the wiring I found one major problem: the orange wire to the right side output was soldered to terminal 9U instead of 8U, and the orange-stripe wire was soldered to 8U instead of 7 U. I fixed this, with high hopes that I had found the problem. However, that did not solve the problem. Instead, I found another.
I did another voltage check, and I tried swapping the 300B's, but saw little difference between the two, so I don't think it's a bad output tube.
However, in touching the heatsinks on the C4S boards, I noticed that the sinks on the L channel were nice and toasty like I imagine they should be, whereas the sinks on the R channel side were much, much cooler. I also noticed that on the R C4S board, the two LED's on the A side of the board were noticeably dimmer than the LED's on the B side of the board. I also noticed that the tube on the R side was running significantly cooler than the L tube.
Redoing voltage checks I came up with the following anomalies:
Terminal 1 at close to zero volts (1.7V)
Terminal 6 at 187V
Terminal 10 at 189V (probably OK?)
Terminal 17 89.1V (probably OK?)
B2 at 88.2V
Something is obviously going on here. That terminal 1 is essentially dead and that terminal 6 is high means something isn't working. The question is, "What?" Ideas?
Thanks,
Scott
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PB will know better, but it looks like there's an issue with the 10V filament supply. It might to helpful to narrow down whether the problem is at the filament supply pcb or after it.
What DC voltage do you read between POS OUT and NEG OUT on the pcb? You should see something close to 10V.
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Hi Derek,
The voltage between POS OUT and NEG OUT on the filament supply is 9.85V, so close to nominal. The boards on both the R and L channels read that same voltage.
To me it seems that the A side of the R C4S board simply isn't getting power. So something before that?
Scott
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More voltage checks.
The transformers are putting out the appropriate 213V (terminals 22 and 25, and 40 and 43), and both IA and IB seem to be getting about 180-190V each, measured directly on the board. OB is reading zero. OA (terminal 6) is reading a little high at 186V or so, on the R channel. The L channel reads nominal.
If OB is zero, why is it that the A side LED's are dim, whereas the B side LED's are bright?
Scott
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I can't really speak to the C4S question, except to hazard a guess that the B+ regulation needs to be loaded by a conducting 300B, and your right side 300B is not really conducting b/c the filament isn't getting the voltage it needs -- but again, this is just a guess regarding the C4S/B+ issue.
But regardless of whether the filament supply issue is related to the B+ issue, I think you have a filament supply problem. If the right side 10V DC filament supply was working properly, you'd see approx. 5V DC at terminal 1 relative to ground -- regardless of what was happening with the B+ circuit. They are two different circuits. The fact that you see some voltage (approx. 1.7V DC) suggests a flaky connection somewhere between POS OUT, PINS A4 and A1, and terminals 1, 4 and 5. If I were you, I would remove the board covering the A-side 4-pin socket and resolder all those connections.
cheers, Derek
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Thanks, Derek. You certainly understand this circuit better than I, and I appreciate your wisdom.
I will go ahead and resolder the 4 pin socket.
Scott
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Resoldered the four pin socket. No change.
Terminal 1 reads 4.86V and terminal 2 is still reading close to zero.
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Do you have the fat pins on the 4 pin socket on that side installed in the correct position?
You have the Neg Out and -reg jumper on each board correct? How about the red wire that leaves POS Out and goes up to the 4 pin socket? On one side, it will go to pin 1 and the other side pin 4.
On each side, there should be a wire leaving the other empty filament socket (either pin 1 or pin 4) and going to the paralleled pair of 10W resistors.
There's a connection in this system that isn't well soldered, or there's a miswire, but it's not easy to tell which. If you were 100% certain that this voltage issue wasn't around before, I would say it's just a flaky connection that needs to be resoldered, or possibly a broken wire.
100% you need to focus on the low voltage side of things before worrying about the other issues that you have.
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Terminal 1 reads 4.86V and terminal 2 is still reading close to zero.
I would resolder the high current C4S board on that side. You could also consider posting some build photos, as we might be able to spot something.
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No wisdom, and very little understanding, I'm afraid. For that you need PB. I've just played around with the filament supply a lot.
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I have checked the tube socket, and it is oriented correctly. I also checked my wiring and didn't see any miswires. I resoldered all the connections around the 4 pin socket, the entire C4S board, all the connections around the power transformer under the filament board, as well as a couple of suspect joints on the filament board itself.
Put everything back together. Applied power. No changes. Terminal 2 still reads close to zero, and terminal 6 reads high. LED's on A side of the C4S board on the R channel still don't light.
I am enclosing pictures for you to help me spot any problems. Perhaps I have just looked at the same circuit too many times to see my faults.
Thanks!
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More pictures.
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Still more pictures.
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Could I get the IA, IB, and OB voltages of the high current C4S board on the side that's not working?
After that, can you repeat those measurements with no 300B in the socket on that side?
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Hi Paul,
Here you go...
With 300B Tube:
IA = 189V
IB = 186V
OB = -0.4V
With 300B Tube Removed:
IA = 192V
IB = 189V
OB = -0.5V
Thanks!
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You can try swapping the high current C4S boards. If the bad voltages follow a board, then we can focus on that. If they stay on that side of the amp, then you know the board is OK at least.
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I swapped the C4S boards. An immediate change I noticed was that now all the LED's were lighting up. However, I also noticed that whereas the R channel C4S previously had been cooler than the L, now it was the other way around. The same "cool" board stayed cool.
Checking voltages, the bad voltages migrated with the change in position of the boards. Terminals 2 and 6, which had previously read as 1.7V and 187V, now read 90V and 146V, just as they should. However, now terminal 11 reads 185V and terminal 17 reads 0.1V.
So the problem is with the C4S board?
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As a further note, I had previously resoldered the entire "bad" (previously R channel side) C4S board, bur resoldered a couple of connections again anyway. I also double-checked that all the components were in the correct locations and in the correct orientations. I couldn't find a problem. I reconnected and retested the board, but with no change. As far as I can tell it's not a bad solder joint.
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I should say, in that last comment, that I reconnected power to the board, not the board itself. I didn't remove and resolder it a second time.
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Terminal 1 at close to zero volts (1.7V)
Terminal 6 at 187V
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Terminals 2 and 6, which had previously read as 1.7V and 187V, now read 90V and 146V ...
Ah ... so terminal "1" in your earlier post was a typo? That's what prompted the recommendation to check and resolder the filament wiring.
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Hi Derek,
Yes, a typo!!! My apologies! I can see how that would have sent you down an entirely different path!!!
You know, I must be getting a bit dull in my "old age." Not only am I making typos, but I am making wiring mistakes, too. This BeePre is my seventh Bottlehead kit, and it's the first one that didn't work right the first time I plugged it in. Usually I am very good at following directions and wiring. In this kit I have found two significant mistakes in my wiring, both simple mistakes that I should have caught if I had been more careful.
I have to say, though, that even though I am having a bit of trouble with this BeePre, overall the Bottlehead kits have been amazing. My undergraduate education is in electrical engineering, but I actually did relatively little with analog circuits and nothing at all with vacuum tubes in my college education. I was mostly into microprocessors and digital logic, so all solid state and mostly IC's. Lots of prototyping with wire-wrapped sockets on perfboards and lots of assembler language programming. Getting to play with tubes has been great fun and very educational. I just wished I had gotten into it years ago.
I really appreciate how helpful the people on these forums are, including yourself! It's a great community.
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My undergraduate education is in electrical engineering, but ... all solid state and mostly IC's.
I'm jealous. No EE education here, and I really struggle to grasp the basics. I am particularly envious of your solid state background. Although BH is known as a tube amp company, I think of BH amps as hybrid amps: tubes "do" the amplifying, but solid state devices (alone or in conjunction with a tube -- e.g., tube shunt regulator) are used to tightly control the amplifying tubes' operating conditions. I think BH's approach of combining the best of tube and solid state is one of the things that sets their amps apart. And, yeah, the community is really great. Which also sets BH apart.
Good luck with the troubleshooting. It looks like you've narrowed down the issue to the board.
cheers, Derek
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Well that's good, you have the issue isolated down to the board itself. You can post more photos of that board top and bottom, and maybe we can see what went wrong. I don't suppose this kit sat around unbuilt for a long period of time?
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Hi Paul,
Here are some pictures of the suspect C4S PCB. I hope that you can spot something, because I have checked this board repeatedly and can find nothing wrong. Every solder joint has been reflowed at least twice at this point. I have also checked that I didn't reverse the resistors on R1 on the A and B sides. You can't tell this from the pictures, though, as I foolishly didn't think to put the resistance values "up" so that they can be seen when mounted to the PCB.
Scott
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More pictures...
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Well, the solder joint that gives people the most trouble is the middle leg of each MJE5731A, but that will typically leave the input and output pads at roughly the same voltage when you don't get it well enough soldered. When you look at the top side of the board, if you see that the solder has flowed through all the holes in the board and up around the legs of those transistors, the joints are probably OK.
Beyond that, if this kit sat around in an area with high humidity for more than six months, the HLMP LEDs may have accumulated some moisture which can cause them to be damaged when you go to solder them. This is a very unlikely scenario, but it happens once or twice a year.
Lastly, it's possible that you have a broken jumper wire on that board. You can gently tug on them with your needlenose pliers to be sure they are all still in once piece.
Beyond that, I would suggest just purchasing a fresh board/resistors/transistor/heatsink/mounting kits.
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Hi Paul,
Well, I thought I had it! For a moment...
I resoldered the MJE5731A'a again, but they looked fine to begin with. No change.
I inspected the jumper wires, but they seemed fine to me. Still, just to be sure, I completely replaced the jumper wires. It seemed to work! The voltage on terminal 11 now read 145V, and terminal 17 read 88V. It looked a little low, but still not bad, so I decided to give it a go on my stereo system.
Plugged everything in, double checked the connections... put on a source... turned on the BeePre then the Kaiju. Put on some John Fogerty, then turned up the volume carefully. It worked! Sweet music came out of both speakers... for about 30 seconds! Then, the left side (the side with the suspect PCB) cut out and all I could hear was a loud static sound in that channel. Turned everything off. Waited a bit, then turned it back on... still more static in the left channel.
Unless you have other ideas, I think at this point I am ready to try a new board and associated components. How much is that going to cost?
Scott
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Oh, and just to answer your other question... this kit sat around for all of ONE day before I opened it and began building. No waiting for me on these delicious Bottlehead kits!
However, I'm not impatient, either. I tried to take my time, allowing finishes to dry and cure, and double-checking everything as I did the wiring. Still, I made two wiring mistakes on this kit, neither of which could, I think, have damaged the C4S board.
Just a bit frustrated at this point that this one is taking so long to get up and running. The thirty seconds of good music that I heard with the BeePre just wet my appetite for hearing more!
Scott
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When you swapped boards, did you unsolder the connecting wires at the board or at the chassis? If you swapped connecting wires too, then maybe try replacing those as well?
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Hi Derek,
I unsoldered the wires at the board, not on the chassis. I carefully removed the wires, then used a desoldering tool to clean up the pads. The wires currently connected to the "bad" C4S board worked previously with the other C4S board. I can resolder again, but I also think that it is time that I tested the transistors. I'm wondering if one or more of them are bad? Seems strange to me that it would work for all of about thirty seconds, then cut out when I turned the volume up a bit. Seems to me that a bad power transistor would cut out if the power got too high, rather than a solder joint. Still...
Thanks!
Scott
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Yeah, that does seem weird. Since you obviously know your way around a soldering iron, why not replace all the transistors? Mouser, DigiKey, etc. could have the replacements at your door on Monday. Faster than waiting for a new board.
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I would do one more board swap, since you had some success with new jumper wires. It's also possible that in swapping the boards, you may have a wire on one side of the amp that's also damaged. I think you're pretty close to being up and running.
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OK, I'll give it a try.
Keeping my fingers crossed.
Scott
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No go. Switching the boards resulted in the voltages going back to the incorrect values they were before, with only a volt or two on terminal 2 and terminal 6 reading high like it did before.
What's more, my probe slipped while testing the (now) good L channel and I shorted out a capacitor. I think it's OK, but it definitely zapped. First time I have done that in a long time.
I think that I had better put down the probe and the soldering iron for a while! At this point I feel like we are chasing the problem in a circle.
Any further suggestions? Thanks!
Scott
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No go. Switching the boards resulted in the voltages going back to the incorrect values they were before
Did the bad voltages follow the board or stay put?
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Hi Paul,
The bad voltages followed the bad board.
Scott
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At this point should I simply order a new C4S board (and perhaps a new capacitor, just in case)?
Thanks,
Scott
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Yes, a new board and the parts that go on it. Definitely do not replace any capacitors.
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OK. Will do.
Thanks, Paul, for all your help.
Scott
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Well, the new C4S board arrived today.
I very carefully assembled and soldered the board and attached it to the rest of the BeePre. I then redid ALL of the resistance and voltage tests. All values were close to spec!
Keeping my fingers crossed, I put the BeePre back into my stereo system. Turned on my Eros 2, the Rega P6, the BeePre, and then the Kaiju. I held my breath as I dropped the needle on to the record...
Hallelujah!!! Sweet music appeared out of BOTH speakers!!! And GOOD music, too!!!
I haven't had time to critically listen to the BeePre yet, but that will be coming later this evening. I can hardly wait!
I can't tell you how relieved I am that we solved this problem. Paul and Derek, thank you SO MUCH for your help with this! I am extremely grateful!
All best wishes,
Scott
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I'm glad you got it going!
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Boy, what a difference! The BeePre sounds worlds better than my previous preamp. The sound really opened up, with greater resolution and dynamics. I feel like I have a totally new and improved system. I couldn't be happier!
Thanks again!
Scott