Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Stereomour => Topic started by: audiotecture on April 26, 2020, 06:21:31 PM
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I ordered/purchased a Stereomour kit January 2013. I’ve successfully built and am using a Bottlehead Crack headphone amp. I finally “finished" my Stereomour kit today and made it through the resistance check fine. During the voltage test, I saw/smelled smoke so I unplugged the amp. I discovered that when I put the 2A3 tubes in for the voltage check I made the mistake of putting them in backward (I did not notice the different size pins and numbers). Reading about similar incidents on the Bottlehead forum it sounds like I may have damaged the tubes, resistors, etc. Rather than attempting to troubleshoot this myself, I thought I’d contact Bottlehead repairs to find out if I might be better off sending my Stereomour in for repair/diagnosis/testing rather than buying new tubes, new resistors, etc. not really knowing what the issue or issues might be. Doc B. suggested I post my issue on the forum in the hopes that Paul Birkeland or somebody else might be able to talk me through testing the transformer and other components to get a better idea of the amp's condition before I send it in for repair/troubleshooting.
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How about you put the tube in the right way and try the voltage check again?
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I rechecked all of my resistance values and all matched the manual. I did a voltage check and all of the values matched the manual. I hooked up my turntable and I'm getting sound from the A-side binding posts but not the C-side binding posts. I also noticed that the PC-3 on the A-side is cool to the touch and the PC-3 on the C-side is hot to the touch. Although there no longer appears to be any smoke, there is a mild smell coming up through the vents when the amplifier is turned on. I've attached a photograph for reference, maybe you'll spot something.
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Turn the amp off and let the power supply bleed down. Measure the DC resistance between HV+ and pin 2 of the 4 pin socket on each side.
-PB
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If I'm understanding your instructions, both measure .59 k ohms.
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You'd want to move the meter down one range to get a more accurate reading if you don't have an autoranging meter.
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(keep in mind my real background is architecture & product design so audio/electronics is not an area of expertise) When I set my Fluke 117 multimeter to autorange, I get a reading of 586 ohms HV+ - C2 & 587 ohms HV+ to A2
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Hey, there you go, you avoided a really expensive problem (toasted plate chokes). What DC voltage do you get between ground and pins 1/4 on each 4 pin socket?
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A1 = 58.4 V, A2 = 362 V, A3 = 0 V, A4 = 59.0 C1 = 59.99 V, C2 = 363.1 V, C3 = 0 V, C4 = 59.8
I'm assuming you wanted measurements with all three tubes installed and the amp turned on/powered up?
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Yeah, those are working voltages.
The plate choke on the side where the tube wasn't inserted properly would've gotten burning hot, and it may need some time to cool off and forgive you.
If the OA/OB voltages on the center PC board are within range, I would suggest listening to the amp.
On the tortured side, that 220uF/250V capacitor on the power supply board that feeds the "K" terminal was probably pretty angry, so you might consider replacing it in the near future. Because your DC voltages look good, the cap hasn't catastrophically failed.
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Thank you Paul. I'm going to play around with the speakers/speaker connections tomorrow early evenig (Eastern time zone) so I may discover something there that may be the issue (I also designed and built the speakers so there's a chance the issue is in the speakers at this point). Sounds like the amp and tubes may not be in as bad a shape as I thought so that's good news.
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Paul,
I just ran a couple more tests and discovered two things that might be additional clues. The A side binding posts are sending a signal to one speaker the B side binding posts are not sending a signal to the other speaker. I thought this was odd since all of the readings tend to be symmetrical. I noticed that the readings at the rectifiers and the resistors on the large circuit board are not symmetrical (see image) testing from C side to A side I get readings of 201.9V (resister left), 402.5V (resister right), 402.5V (rectifier left), 201.2V (rectifier right), 201.2V (rectifier left), .003V (rectifier right), .003V (resister left), 201.9V (resister right). Something doesn't seem right about reading on the A side rectifier right and resister left? Any thougths?
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What are the DC voltages on each of the 4 pin sockets? If you have 200V coming out of one side of the power supply board, ALL of your DC voltages on one side of the amp will be incorrect.
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A1 = 59.25, A2 = 361.1 , A3 = .008, A4 = 59.42, C1 = 59.84 , C2 = 362.3, C3 = .008, C4 = 59.70
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Your power supply board is working.
The Stereomour will produce a little 60Hz hum at the binding posts, can you hear that on both channels?
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I suspect my hearing is not good enough to hear hum at 60Hz :(
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You can put your finger on a speaker cone and feel the 60Hz.
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I can hear/feel the hum from one pair of binding posts (closest to inputs) but nothing from the other pair.
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OK, so there's an issue either with how the output transformer is hooked up on the tube side or the speaker side. This could be missing or poorly soldered jumpers on the output transformer, poorly connected or missing wires from terminals 5 and 10 on that output transformer, a loose 3.3uF/630V capacitor, etc.
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I went back and checked for missing wires (none that I could identify) and resoldered a number of connections in the areas that you described. Blew the fuse when I restarted the amp. The supplied fuse reads F1.5AL250V the manual reads 1.5A GMA slo-blo fuse. I'm having trouble tracking down replacement fuses online. It seems the supplied fuse and the fuse described in the manual are different fuse types? Can you clarify the proper fuse type and perhaps point me in the direction of an online source. Troubleshooting will need to wait until I get replacement fuses.
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A 1.5-3 amp fuse of the appropriate size is fine (5x20).
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Paul...finally received my replacement fuses. I retested all of my voltages and there are a few that aren't quite right. Terminal strip 11 = 160V, 15 = 268V, 20 = 160V, C1 = 160V, C2 = 268V, C4 = 160V. Similar to before there is sound coming out of the A side binding posts, but none from the C side binding posts. The PC3 on the C side warms up when the amplifier is turned on, but the PC3 on the A side remains cool.
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Heat in the plate choke is determine by the voltage at the HV+ pads on each side of the amp vs. the voltage at pin 2 on each 4 pin socket across the resistance of the plate choke. So for the heat dissipated in the plate chokes to be different, you need voltages on the 4 pin sockets that are completely different from each other or the DC resistances of the chokes need to be way, way different (which would indicate a damaged choke).
I have provided you the instructions before to check for each of these conditions, and you didn't find either issue. I would strongly recommend redoing these checks. For the one plate choke to get hot but not the other, there has to be an accompanying result that indicates why.
So when I went into the manual to see what might be going on with your voltages, I can now tell that your 4 pin socket voltages aren't the same between sides. Seeing 160V at terminal 11 is not a good sign. The rest of these are all kind of a result of that. I suspect that the 5W/10W resistors mounted to the terminal strips on that side of the amp are loose or damaged.
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Paul...I took the resistor out and when I tested it, it showed 231.8 ohms of resistance. Looks like my local Microcenter has 220ohm 1/4watt resistors in stock. I should be able to pick them up, replace the existing resistor, and test again tomorrow.
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No, put that resistor back!
There is a 5W and 10W resistor connecting between the two 5 lug strips around the 9 pin socket (a 1.6K and a 4.7K). Either one of those is damaged or one of those is not connected (maybe both).
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Paul...I think I found the source of the smoke I saw/smelled when I initially powered up the amp with the tubes in the wrong orientation. You can see (in the attached photograph) that the heat from the 10W 1.6K resistor melted the insulation on the red wire between B6 & 14L & singed the socket screw/washer. The 10W 1.6K resistor measures 1.7K ohms of resistance. The 5W 4.7K measures 4.58K. The 220-ohm resistors both measure around 220 ohms of resistance.
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You can put that all back together, disconnect the "K" wire on the power supply board on that side, then measure DC resistance between ground and pin 1 on the 4 pin socket on that side, then ground to pin 4 on the 4 pin socket on that side (powered off).
-PB
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Paul...Finally had time to put everything back together. I disconnected the "K" wire on the power supply board. Ground to pin 1 and pin 4 on the 4 pin socket are 1.255K ohms (on the side that's not working) For reference measurements on the Ground to pin 1 and pin 4 on the 4 pin socket on the side that is working are 1.168K ohms
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You can leave the wire to K disconnected, recheck DC volatges on all four pins on the 4 pin socket on the bad side and report back.
That resistance is totally fine, those resistors are good. There could be something amiss with the wiring to pin 3 of the 4 pin socket that's not allowing for it to get a good ground reference. That is the 249K resistor and the 220 ohm carbon comp grid stopper. Be sure those are well connected.
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You can also swap the 2A3s to see if the voltage issue follows a tube.
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Swapping the 2A3s the reading at A1 is 1.167, A2 * (number keeps getting bigger), A3 248.7, A4 1.167. I don't know if it means anything, but when I did my resistance check, terminal strip 2 & 14 settled at 687K ohms rather than 486K ohms. Terminal strip 7 & 9 are at 15.79 and do not change when the potentiometer is turned. I've also included a photograph of 4 pin socket A. One of the soldering holes broke off at A2 so both wires are soldered to the remaining hole. Not sure if this makes difference?
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Swapping the 2A3s the reading at A1 is 1.167, A2 * (number keeps getting bigger), A3 248.7, A4 1.167.
Voltages?
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Paul...I'm not sure if this is the information you are looking for, but I've detached the black wire from K on the power supply board on the A side and I get the following readings A1 = 59.6V A2 = 362.2V A3 = .008V A4 = 59.5
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That's a perfect set of DC voltages. before you had over 100V at A1/A4. Now you can put the K wire back and recheck the DC voltages again.
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Paul...I replaced K on the A side of the power supply board and now have the following readings A1 = 59.27V A2 = 360.2V A3 = .007V A4 = 59.30V for reference C1 = 60.57V C2 = 363.1V C3 = .007V C4 = 60.42
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Those are working voltages.
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Paul...Given the similar measurements on the A & C sides, I attempted to play music and observed the following: If I plug speakers into the A-side and C-side speaker binding posts, sound comes out of the A-side but not C-side. If I take the C-side red cable and touch it to the A-side red binding post, I get sound from both speakers. Touching the C-side black cable to the A-side black binding post does not produce any sound from the C-side speaker.
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Turn each hum pot all the way clockwise. Do you hear hum in both speakers?
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Paul...yes I hear hum in both speakers.
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There's wiring that leaves pin 1 and pin 6 on the 9 pin socket to send signal to each 4 pin socket. I suspect that yours is loose on the side without sound. Since you can hear hum and I'm guessing it's roughly the same level, the 2A3s are operating properly and the output transformer wiring is OK.
If the DC voltages at OA and OB on the 9 pin socket are OK, then that leaves the wiring leaving pins 1 and 6, or possibly signal isn't making it into the 9 pin tube from the input selector and volume pot.
To test the input selector and volume pot, temporarily install a jumper between terminals 7 and 9. This will sum both channels and send that mono signal to both sides of the amp. If your dead channel awakens, then you need to inspect the wiring from the RCA jacks to the selector switch, the selector switch to the volume pot, and the volume pot into the amp. If both channels stop working, that is also an indicator of an issue with the input wiring. If the same channel is still dead, that's an indication of a remaining wiring issue around the 9 pin socket, or possibly the .1uF coupling cap.
-PB
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Paul...DC voltage at OA = 212.1V & DC voltage at OB = 209.7V. The jumper between terminals 7 and 9 worked sound came out of both the A-side and C side. I checked all of my wiring and connections from the RCA jacks to the selector switch and selector switch to the volume pot and volume pot into amp. Almost perfect good news. RCA jacks 2 & 3 are sending a signal to both speakers. RCA jack 1 is still only sending a signal to one of the speakers. I don't have any more time tonight to troubleshoot RCA jack 1, but I'm assuming I'll just need to re-check all my solder joints and connections. Is it possible to damage an RCA jack during soldering?
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Yes, you can damage a jack. If solder flows between the center of the RCA jack and the shell, it will short out the signal. 99% of the time, this is what we see going wrong. If you measure the DC resistance between the center pin of the jack and the outside body of the jack with the selector switch not on that input, it should give you a very high resistance (or over limit). If solder has shorted the jack out, then you'll see something close to zero ohms.
I have also seen debris get into the bottom side of the jack between the center pin and shell, and that was enough to create the same problem.