Bottlehead Forum
Bottlehead Kits => Stereomour II => Topic started by: Smoses01 on October 18, 2023, 09:13:05 AM
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Hello, I have a completed stereomour II amp I am trying to troubleshoot. Initially, I had B+ voltage on one side only. I reviewed my connections and re-heated and added a bit more solder to connections that looked not too secure. Now, I have no B+ power to either of the large tubes.
Also, I notice that the LEDs aren't lighting on the Cs4 board. I have gone over everything and cannot find the problem. My next step seems to be returning the unit to Bottlehead for repair. I thought I would try the forum before doing that. My resistance checks were all ok, and my voltages when testing the power supply were all normal. Any suggestions?
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Can you post some build photos? Did the fuse end up blowing?
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no blown fuse. I think the problem may be with where 130 2 W resistors connect together right before B+ power occurs on circuit diagram. Will post some photos. I certainly don't want to take step of sending unit back to Washington state unless absolutely necessary!
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_MG_4553 copy.jpg
Trying to post an image of where I think problem is occurring. not sure if copy of jpeg has posted correctly, but here is a link:
/Users/stephenmoses/Pictures/Photos Library.photoslibrary/originals/D/D6A28395-3008-45CC-9D61-28F3D0E8E67D.jpeg
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To attach a photo, click on the "Attachments and other options" just below the text box. Note the list of acceptable file formats and the maximum size. PNG files are acceptable.
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Today I have reviewed every joint in my build. Re-heated questionable connections, and added a bit more solder where needed. I also performed the primary and secondary voltage test on the power supply ((all were normal).
Resistance tests all good. But when go to do voltage tests, I am getting no high voltage at all. I start at the top, getting AC 120 coming in from the plug to the first small circuit board with 45, 46’ 47, 48 terminals. Then I check dc voltage at the ultrafast rectifier and get weird readings like -1.85 or such. I keep moving towards the front of kit and check every spot where B+ high voltage should be occurring, and instead of 388 volts I once again get a weird readout like -1.85.
Then going directly to the 2A3 tube sockets I get similar( -) voltages. Also, as before, LEDs on circuit board are not glowing. A few days ago I removed the circuit board, checked for proper soldering connections and re-installed it.
I really don’t want to have to return my unit to Washington state, but I am lost as what to do next. BTW, I am using a good quality meter- a Fluke 177. Stephen Moses.
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Don't worry yet - we have a good record of resolving problems like this through the Forum. It just takes a little time to be methodical. You have the attention of the guy who did the mechanical layout of the SII (and our chief technician) PB, as well as the circuit designer (myself). Photos of the build are usually a big help; be sure to include the area of the UF4007 rectifiers.
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This is going to be something missing or backwards. Build phots will help to make the issue more obvious.
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Here are a few pics:
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pics:
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more pics:
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more pics:
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pics:
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I'll go through these 1 at a time.
In this photo, there are several problems. The wire going to pin 9 on the tube socket isn't routed properly and is potentially touching the resistor leaving the center post of the socket. If this happens, you're likely going to smoke the power transformer.
The resistor going from the center post to pin 8 on the tube socket isn't properly routed and is extremely likely to cause operational issues with the amplifier.
The tinned buss wire going to the center post needs to be routed right between pins 1 and 9 right in the middle.
I would review how these components and wires are routed in the manual and make corrections where possible. If it touches pin 9, that will damage your power transformer. If it touches pin 1, that could damage your C4S board.
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In this AC input wire, the foil shield on this shielded twisted pair wiring is earthed to the chassis. The metal strip on the IEC power entry module that it looks to be touching carries 120V AC. If these two touch, you will constantly blow fuses.
I have attached the photo from the manual of what's desired.
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There seems to be a missing black wire here.
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Can you carefully measure the voltage between terminals 41 and 44?
I would suspect blowing fuses should happen based on the photos, but if you are getting proper AC voltages coming out of the power transformer, you should see about 400V appearing between 41 and 44. If you have that voltage there, but it's not making it out of there, then there's going to be a soldering issue or a missing wire.
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I’m getting 0.235 volts dc. Strange!
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I will carefully review what you have commented on from my pictures. Thanks!
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With the crazy voltages I have been getting, I almost suspect the power transformer is not working correctly, but I did the primary and secondary voltage tests, as per the instructions, and they were normal.
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I have previously successfully built a crack amp and a sex 3.0 kit. Unfortunately, with the past few years in my early 70s, I have developed some shakiness, which is not very good for successful soldering outcomes. Still, I would like to get my Stereomour II kit up and running. It's possible I may need a new power supply, what with no B+ power coming to either channel. I guess the best thing at this point is to return my unit to Bottlehead for repair.
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How do I find info for submitting a support ticket? I have checked the forum page, but can’t find anything relevant to submitting a support ticket. Thanks!
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With the crazy voltages I have been getting, I almost suspect the power transformer is not working correctly, but I did the primary and secondary voltage tests, as per the instructions, and they were normal.
If the proper voltages are coming out of the power transformer, the power transformer is not the problem.
If you use your meter to measure a 9V battery, what voltage appears on your meter?
Your wiring around 41 and 44 looks correct, and a short that would drag that to 0V would burn up the 130 ohm resistors, so I would expect to see about 400V DC there.
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Just discovered an unattached white wire where couldn’t see it because was in area of 42u. That would explain lack of B+ power. Will re-attach and see what happens.
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Ok, I have re-attached a loose white wire to 42L and now have B+ voltage to one side all the way down to the large tube. All along I never have had B+ voltage to the other side. I did a continuity test on the working side and there was continuity between the red wire on the bottom of the plate choke to the red wire on terminal 1. Not so for the other side. I think I may have strained a wire when pulling them through the hole near the plate choke. What is the cost of a new plate choke?
Thank you.
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With the amp off and the power supply discharged, set your meter to DC resistance. Now measure the DC resistance between the blue and black wires on the plate choke you believe is bad. Now compare that to the resistance reading on the blue and black wires on the plate choke you believe is good.
For what it's worth, I cannot ever remember a plate choke being damaged in this manner.
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I am getting approx.1 ohm of resistance on both sides between the blue and the black wires.
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Though that is completely wrong, it would not prevent B+ from appearing on either 4 pin socket.
Can you post the voltages on each 4 pin socket for pins 1-4?
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A1: .007 dc
A2: 0
A3: -.0.963
A4: .006
D1: 64.84
D2: 386.6
D3: 0.020
D4: 64.88
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It seems pretty clear that the D socket is getting normal voltages, while the A socket is not. I will recheck all connections that convey power to the A socket. Thanks for your help in diagnosing this problem.
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I would follow the DC voltage along the 130 ohm resistors as it goes toward the A socket to see where it's dropping out. Do also be aware that a missing or loose black wire along the same path would create the same problem.
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A1: .007 dc
A2: 0
A3: -.0.963
A4: .006
D1: 64.84
D2: 386.6
D3: 0.020
D4: 64.88
One other question- I continue with no LEDs lit on the C4s board. So, would that be connected to no B+ voltage on The A channel or is it a separate issue entirely? Since the C4s board processes the sound signal To the small tubes, you can have B+ voltage ok to the 2A3 tubes, (the output tubes), but no sound signal being processed to the first stage tubes.
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A1: .007 dc
A2: 0
A3: -.0.963
A4: .006
D1: 64.84
D2: 386.6
D3: 0.020
D4: 64.88
One other question- I continue with no LEDs lit on the C4s board. So, would that be connected to no B+ voltage on The A channel or is it a separate issue entirely? Since the C4s board processes the sound signal To the small tubes, you can have B+ voltage ok to the 2A3 tubes, (the output tubes), but no sound signal being processed to the first stage tubes.
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Would resistance between black and blue wires of 620k ohms for both Channels be reasonable figures? I configured my chokes for 8 ohms.
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Re-tested impedance on each plate choke and I am getting 6.2 ohms on each side.
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Correction on rechecking each side reading 6.2 ohms impedance between black and blue wires from plate chokes.
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I would focus on getting the DC voltages correct on the 4 pin sockets first before worrying about the C4S board.
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Would resistance between black and blue wires of 620k ohms for both Channels be reasonable figures? I configured my chokes for 8 ohms.
That would be your output transformers, not your chokes. I would focus on tracing the B+ along the 130 ohm resistors to see where it's dropping out and not be too concerned about the chokes right now.
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I have checked where voltage drops off: here is an overview of major high voltages I got, as well as areas of concern that are starred: thanks for any assistance that can be given!
Voltage checks:
*1-2: 0 volts dc
14: 170-230
19: 418
20: 418
20: 385
*27: 0 volts
*30: 0 volts
31: 418
34: 418
IB: red wire to printed circuit board: 418v
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44 and 30 aren't connected properly by the 130 ohm resistor, it's missing, or it has burned up (which would be very visible).
A blown plate choke would give you 400V at terminal 27.
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Big goof! I accidentally shorted my power supply! (Sparks and loud pop). Now I have no B+ power on the side was working correctly. Interestingly, voltage checks to primary and secondary are normal. Also, I’m still getting high voltage 400 volts at the rectifier right at the connection
To the power supply. Checked the tubes and they appear to be ok. I think that I will need to replace the power transformer and any other parts that you think may have been damaged with the short. What do you think? Thank you!!
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I think that I will need to replace the power transformer
Why?
If you read back through this support thread, repeatedly you have asked to purchase replacements of the most expensive and most difficult to replace parts in this kit, and there has never been any data presented on your part that would necessitate having these items replaced. Even in the event that one of these parts needs to be replaced, we have to sort out here why it failed in the first place so we don't sell you an expensive transformer only to have you install it immediately damage it in the same manner that caused the original part to fail.
Any parts requests like this that get sent in will get reviewed pretty carefully so we don't end up in this situation and also to be sure we aren't replacing components that haven't actually failed. We also have written into the manual a set of checks to verify proper operation of the power transformer and performing these tests is the first step (but not the only step!) in determining if there's a power transformer problem.
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You are absolutely correct. The last thing that. I want to do is replace an expensive part like the power supply unless it is absolutely necessary. When I accidentally short circuited my power supply and saw sparks and heard a pop, I thought it was very bad news. Then, when I checked for B+ power on the side that had been working properly, I saw that there was none combing to the 2A3 tube spot. I will do things a bit more methodically from now on. Thanks, Stephen Moses.
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Always check the fuse first...