Bottlehead Forum
Bottlehead Kits => BeePre => Topic started by: Kurthaudio on December 03, 2021, 06:34:04 AM
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Hello again,
Short version:
#14 to 30: 9.6vdc
14 to 16: 87vdc
14 to 11: 175vdc
14 to 25: 0.9vdc
14 to 6: 45vdc
14 to 1: 175vdc
Some of the parts look different then stock. That’s because they have been soldered and desoldered to many times so I replaced them with equal values of what I have laying around.
I switched the tubes and the voltages stay exactly the same. I switched out the 100k pot again exact same voltages. If I disconnect the b+ voltage wires I get 260vdc as soon as I connect them it drops to 175?
This kit is kicking my but and once again I’m at a loss………
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Here is a pic
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You need more heat on those solder joints, most of them look pretty cold.
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I can assure you they are not cold joints it’s Mundorf supreme diver gold solder and that’s just how it looks.
I do have several hounds that are not soldered until I get this voltage issue sorted
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Any other help?
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I'm certain that 12 and 14 are cold. Balance control and the adjacent terminal strip look to have no solder, just solder them and don't worry about getting the voltage problem solved. How do you know that the unsoldered joints are not causing the problem?
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I know because I had this problem while everything was soldered. 14 and 11 are not soldered thats why they look like they are cold joints.
When I changed the balance pot I ran new wires and did not solder them. I wanted to leave them until I found out why I’m having this issue. To keep this from getting confused I’ll solder everything up take new readings and report back.
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Holy smokes, there is an awful lot of silver in this solder 9.5%
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Ok guys, I soldered everything up. I’m still getting the same voltages as posted in my first post.
B seems ok with 14 - 30: 9.6vdc and 14 to 16: 87vdc
A seems to be my problem. I’m getting 14- 25:.9vdc and 14- 6: 45vdc.
Is it normal to be getting 175vdc @ 11 and 14?
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Lol solders like it too >:(
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Not having a beepre 2 I can't be certain but it looks like 11 is getting the b+ to the plate and 14 is ground. S measuring between 11 and 14 could show 175vdc. What voltage do you get on the equivalent terminals on the other tube?
/
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Yes you are correct 11 is B+ and 14 is negative
The solder tabs are basically just a junction that routs wires down to 1 and 4 of the A socket. I’m getting 175vdc at both 11 to 14 and 4 to 1
Earlier in the build the instructions ask for voltage check of the B+ power supply before it’s connected to anything and I get 260vdc. (250 +/- 20%)
It seems odd to me that once connected it drops to 175vdc?.?. Shouldnt it remain 260vdc?
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No i'ts not funny, that's the plate voltage at the operating point. If you pull the tubes out the b
+ will jump back to about 260vdc. You have a voltage drop of around 45vdc due to the cathode resistor. No worries, march on soldier.
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Ok. Thank you clearing that up.
But how in the world am I only getting 45 volts at 6? And only .9vdc at 25? I do have 175@ 1.
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As I stated earlier, I do not have a Beepre 2 or the schematics. My advise is follow the instructions, solder when told to do so, and preform any resistance and voltage tests when directed to do so. And then if any problems turn up than that's when to ask questions.
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That’s what I’m doing, I’m at the point where I should be getting 10vdc and 100vdc and I’m only getting 0.9vdc and 45vdc. I cant get past this thats why I am asking for help right now.
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That’s exactly what I’m doing.
I should be getting 10vdc and 100vdc on 25 and 6 respectively
I’m getting 0.9vdc and 45vdc……that is what this thread is all about. I’m asking for help to figure this out.
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I'm sure either PB or PJ or if you are lucky PB&J will chime in and get you sorted out. I did about all I can do without being familiar of that product. Don't get to stressed out, you'll be fine in the end.
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Thanks brother. I needed to hear that. I am getting a bit stressed about this. Lol. Thank you for your help. I did learn a little.
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A seems to be my problem. I’m getting 14- 25:.9vdc and 14- 6: 45vdc.
This needs to be cleared up before you continue. There could be a loose connection at pin 3 on that socket which isn't providing the grid with a solid reference to ground.
It's also possible to plug the 300B into the socket with the fat pins not in the bigger holes, though it takes some force to do that. If this is done, you can get weird voltages.
It's going to be tough to provide much more assistance beyond that, as all the parts in this preamp are not the parts we provided, so there isn't much of a way to visually compare.
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The parts used in this preamp are either the same quality or higher. The values have been checked double checked then rechecked time and time again. I used my fluke 902 to measure most values I used my LCR meter to measure the rest. to be 100% certain they are the correct values. I also had these exact voltages with the stock parts
I can re-install all the original parts if you would like to show I’m getting the exact same problem.
The tubes have not been installed backwards
The tube sockets are installed with larger pins to the back as stated in the instructions.
Let’s just assume all values are installed correctly and all pins are in good contact. All solder joints are properly soldered. Would a set of bad tubes (possibly damaged from my first attempt) possibly cause this? If not……. What should be my next step to get this resolved?
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I just want to throw this out as well, everything measures good without the tubes I stalled
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If you swap the tubes from side to side, do the problematic voltages stay in the same place or migrate to the other side of the preamp?
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Paul, That’s what makes this even more confusing. Swapping the tubes makes no difference.
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OK, then you have an issue with the wiring on that side of the amp.
As I mentioned before, if A3 isn't well referenced to ground, that will throw things way off. This is extra possible if there are cold solders or unsoldered joints.
If you replaced the cathode resistor with a different value (like 33 ohms instead of 330), then that would create this exact problem.
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Agin. No cold solder joints ( I know how to solder very well) no un- soldered joints as shown in my last picture. 330 ohm is used.
I have built many kits. Several from Tubes for hi fi including 6 m-125 monoblock amps. Two Chinese phono stages, a bottlehead phono stage. Countless speakers over the last 20 years. I have made miles of soldered connections. I know what a cold joint is and I know what it looks like.
I understand you get a lot of solder issues on this forum. This is not a solder issue. Something else is going on here and to keep referring to a cold solder joint is not helping at all.
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0.9V of bias and 45V on the plate means the 300B is drawing too much current.
You can temporarily solder in a wire between pin 3 on the 300B socket at terminal 4 to give the grid a solid ground reference to see if that changes anything.
Otherwise there is something amiss with the three resistors and the cap on 21-25. The 0.9V would indicate a near short in that area. If you take the capacitor off that terminal strip, what is the DC resistance between pin 1 and ground? ...and pin 4 and ground?
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With the 220 cap removed
Pin 1 - tab 3: 447.3 ohm
Pin 4 - tab 3: 449.2 ohm
Jumping pin 3 to tab 4 doesn’t change anything still .9vdc at 25 and 45vdc at 6
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How about the voltages with no 220uF cap?
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Voltage does not change with the 220 cap removed.
I tried it with the 220 cap removed. No change.
Jumped pin 3 to ground (tab4) with 220 cap removed. No change
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With one probe clipped to terminal 4, what voltages do you get at:
14, 15, 21, 26.
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I get 0 Vdc at 14, 15, 21, 26
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There is something that's missing in all this, but I have no idea what it is.
0.9V across ~400 ohms is 2mA.
The 130V you are measuring across the 3K plate load resistor is more like 43mA.
There should be no difference between these two.
These two measurements are contradictory, and when I see stuff like this, I tend to expect that a flaky solder joint is at work. I know you are not going to be happy with that suggestion, but you have more or less ruled everything else out. The only other explanations I could think of are ruled out by taking the bypass cap out and confirming appropriate resistance to ground from terminals 1 and 4 on the 4 pin socket.
It may also help to get a photo of the 21-25 terminal strip with no cap installed, just to double check everything.
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Paul, maybe I’m missing something here but what 130v are you referring to?
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130V is the voltage across the 3K plate loading resistor. 130V/3K=43mA.
When looking at the 300B datasheet, 75V on the plate and 43mA of current does indeed happen with approximately 0V of bias.
The question with your preamp is why the bias voltage is so low (43mA drawn through that 330 ohm cathode resistor is 14V of bias!). Something that would be super typical that we have run into in a situation like this is that the cathode bypass cap gets installed backwards, fails, but the builder will notice and reinstall it. Instead of the DC operating current flowing through the 330 ohm resistor, it flows through the shorted cap. In your case the problem exists without the cap there which further extends the mystery.
For your kit, can you post the DC voltages between terminal 4 and:
21, 22, 24, and 25?
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21: o
22: 4.7
24: -1.4
25:1.3
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Paul, do you see any possibility that the tubes themselves could be causing this?
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If a tube was the problem, the problem would move to the other side of the amp when swapping tubes around.
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OK, here's what I can see from your measurements...
The 6.3V filament supply sits on terminals 22 and 24. Those terminals are both connected to pin 25 by 130 ohm resistors. 6.3V divided by the 260 ohms (the two resistors in series) is 24mA, which would be the expected current with a 300B sitting in the socket but no current being drawn from the HV supply.
Between 22 and 25, we see 3.4V, 3.4V/130R=24mA.
Between 24 and 25, we see 2.7V, 2.7V/130R=21mA.
These measurements tell me that nearly no current is being drawn across these resistors beyond just having the 6.3V filament supply active.
1.3V at terminal 25 indicates 4mA of cathode current, but this is a contradiction to what's going on with the HV side.
Just for curiosity's sake, if you run no 300B in the A socket with just a 300B in the B socket, what are the voltages at terminals 1 and 6?
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With tube in socket B and nothing in socket A I get tab 1: 216.8vdc Tab 6: 0vdc
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With tube in socket B and nothing in socket A I get tab 1: 216.8vdc Tab 6: 0vdc
0V at terminal 6 is nearly an impossible result. Are both ends of the 3K resistor well connected? Perhaps the solder joint at 6U isn't doing its job?
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I just double checked and yes I’m getting 0vdc measuring from tab 4 (ground) to tab 6……….
The resistor measures 2995 ohms
P.S.
Just in case this is the first time in my life I’ve ever been wrong (lol) I reflowed all my solder joints. Related to socket A. Unfortunately Same results.
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I cut out that resistor and soldered in a new one. Now I get about 215vdc on 6. And 216 on 1
Installed the tube and voltage drops to about 50 vdc @6
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Can I see the other side of terminal 6?
With no tube in the socket, there's nothing to draw current through that resistor, so seeing 0V at terminal 6 indicates an issue with the amp that isn't tube related.
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Yes sir.
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That's terminal 5.
I definitely would not have just removed the resistor and arbitrarily replaced it. That just adds more variables and you weren't able to measure any issues with it.
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You asked to see the other side of terminal 6…… that would be terminal 1.
Here…. Here is a shot of all of it.
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My apologies for replacing the resistor I didn’t see the harm in it.
I am just trying to get this figured out. This has been going on for a few days now and I’m no further now then I was when I began. I don’t want to sound ungrateful for your help, I am but this is turning into a giant headache. If I didn’t have this amount of money tied up into this I’d of moved on with my life by now.
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It would be helpful to see the back side of terminal 6.
If you had the configuration still with 0V at terminal 6, I would have next instructed you to measure the resistance to ground from terminal 6. Now that opportunity is lost.
Are these the 5 lug strips we provided? Very rarely the 5 lug strips we provide go out of stock and we have to provide alternatives, though it's pretty rare.
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No these are not the stock standoffs.
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What is this?
To be honest, starting over and using stranded wire and the parts we provide would likely be the best idea. I hadn't noticed the stranded wire till now, and it is absolutely the kiss of death on builds like these.
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That’s the center tab bent in slightly.
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Could you explain why stranded wire is the “kiss of death†because that same stranded wire is working just fine on socket A
I’d be willing to bet you don’t want stranded wire used in these kits because one could easily have a small strand of wire make a connection where one shouldn’t.?. Something else I’ve been diligent about.
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Yes, the strands go where you don't want them and the wire doesn't stay where you put it. It's also both harder to make solid mechanical connections with stranded wire and tougher to move a wire if you don't put it in the right place.
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Ok I just found something that is very important, I switched the wires from the regulator board and the problem followed suite. Now socket a has all the voltage issues socket b had and socket b is working correctly!!!!!
I think this says I have a bad regulator……right?
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No, please resist the urge to blame parts as much as possible.
A bad regulator will result in not having 6.3V appearing between the output pins on the filament regulator board, is that what you're seeing now?
If one of the wires leaving that regulator board is touching something it shouldn't be, that could cause this problem.
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Nothing is touching anything it shouldn’t. No Cold solder joints and yes it’s making a sold connection.
Don’t worry I will not change anything g unless you tell me to
They both measure 6.2vdc exactly with nothing connected to them.
However I did notice the tube that has the voltage issue doesn’t get as bright as the one that’s working correctly……
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Can you measure the DC voltage of each pair of regulator terminals that feed to the sockets?
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6.2vdc A
6.1vdc B
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Your regulators are doing their jobs. This board does not have any reference to ground that will compete with the biasing resistors mounted by each socket, and your resistance readings also seem to confirm that this is still the case.
What I would do next is to pop both pairs of black/red twisted wires out of the regulator board, then measure DC resistance between terminal 4 and each of the four now empty output pads on the filament regulator board.
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Ok I get OL resistance from 4 to the now open pads. OL on all of them individually.
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Now do the same test on the loose ends of the wires that are no longer soldered in.
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393 red to 4
393 blk to 4
396 red to 4
396 blk to 4
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Could you post a picture of the bottom of the filament supply PC board?
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Yup.
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If I switch the 6.5vac coming off the transformer to the filament board the problem will follow. However I get 6.5vac on both sets with nothing connected????????
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Problem solved. I have a AnTek AS-05T240 transformer laying around from another build. I removed the PT-9 6.5vac secondary’s and plugged in the AnTek………BINGO!!!!! Everything checks out now. Something is wrong with the low voltage windings of my PT-9 transformer………...
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Can you completely remove the filament PC board and show us what the wiring looks like on the transformer?
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Sorry I already removed the PT-9 and installed the AnTek and am listening to it right now.
I really like what I’m hearing! I have a little his/hum in between songs. Can’t tell if it’s tube rush or ground hum. Right now I don’t care this thing sounds beautiful!