Bottlehead Forum
Bottlehead Kits => S.E.X. Kit => Topic started by: Dana Hinds on September 05, 2022, 04:09:29 PM
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Power and resistance values were all good, finished and powered up. Heard snapping noise and saw some smoke, only one channel was working. After looking it over the only problem I found was I missed soldering one resistor to terminal #16U. Looked like the 680 ohms resistor that goes from 21U-33U was hot. Looked everything over a hundred times and all else seems ok. I now do not get proper resistance reading from terminal 17, 18, or 25 to H1. Not sure what to do next. Any help would be appreciated.
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Can you post some build photos?
Your voltage checks should have been way off if you ended up with that situation. If the 680 ohm resistor going to 21 got hot, two component leads on that side of the amp are probably touching that shouldn't be.
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Here are the pictures. Thank you.
Dana
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Here are some more pictures.
Dana
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Remove the red wire from 21, bend it up into the air, then fire the amp up and check the DC voltage at 21.
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From terminal 21 to h1 I get 500v
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If the amp is happy with this wire disconnected, this tends to mean that something is touching around that socket that shouldn't be. You may want to remove the Solen parallel feed cap and post more pictures and we might be able to see what's causing the problem.
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Here are some more.
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I still see no issues. Something else you could try is to put the disconnected wire and cap back, then run the amp with no tube in that side and recheck the voltage at 21 (it should remain high).
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Voltage stays at 500
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Put the tube from the other channel into that socket and see what happens.
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I installed both tubes, nothing seemed to overheat and no smoke.Plugged in headphones and only have one channel.I noticed b side plate choke was warm when running and a side plate choke never got warm.
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The voltages are of interest here, not attempting to listen to an amp that isn't working yet.
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Doesn’t seem like a side may be getting power
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So the information I'm looking for is something like "The voltage at terminal x is supposed to be y but instead it's z".
Without that kind of information your guess is as as good as mine.
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sorry I am going to go back through everything ,just getting frustrated.
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I have gone through all assembly to make sure of connections or shorts , found nothing. Wondering if the miissed solder connection on resistor to terminal 16U may have taken out a capacitor or something.Lokking for the next step.
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Probably want to start with running the resistance and voltage checks and listing any that are out of spec here.
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before power up normal ,now here's what I get
Terminal #1-0 #3-891 #4-240 #5-0 #8-0 #9-0 #11-678 #12-0 #14-0
#15-0 #17-218 #18-5.5 #19-0 #22-0 #23-0#25-0 #26-0 #36-0 H1-0 H8-0
looks like 17,18,25, are way off
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Are those voltages or resistances?
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resistances
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I would be most concerned about terminal 25 reading 0 ohms. Two wires, one capacitor, and one resistor land there. Remove each of those one at a time and recheck your resistances as you go until you don't see a 0 anymore. I would start with the cap, then the resistor, then the white wire going to the OT, then the white wire going to the socket.
You can stop when you find the connection that's dragging that terminal to 0 ohms and let us know what it was.
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with the cap removed I get 678k ohms
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Hopefully 0.678K?
You can actually run the amp with the cap removed to check DC voltages, but if you try to listen to it that side of the amp will be quieter and more distorted than the other side. In any case, I'd go ahead and replace it. I can remember getting on SEX amp in the past that had a dead cathode bypass cap like that, and I remember that there was something that I thought could have precipitated the failure, but I can't remember what it was.
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great where is the best place to source one
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I now have voltage readings that are off. all are good except terminal #17 has 63v and #18 has 59v should be 15 and 0
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So what's going on here really is that the voltage on terminal 18 is not 0V, and that is screwing up everything else and has allowed excess voltage on that cap that's shorted out.
There's a 249K resistor between 18 and 19, does it still measure as 249K? If so, take the tube out of that socket and set it aside, then take the tube from the other side of the amp and try it in that socket to see if that same pesky high voltage is there.
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I only get 95k on the resistor
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I would heat up the solder joint holding one leg of the 0.1uF cap in place and pop one lead of that cap off the terminal strip, then recheck that resistance.
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I now get 249k
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This kind of failure can happen if the cap is snugged up too tightly to the terminal strip and possibly gets melted a bit so that it contacts other terminals or internally shorts. This is generally what we are providing these days:
https://www.parts-express.com/Jantzen-0200-0.10uF-400V-Crosscap-Capacitor-027-900 (https://www.parts-express.com/Jantzen-0200-0.10uF-400V-Crosscap-Capacitor-027-900)
I would replace that cap, recheck that resistance again to be sure it still shows as 249K, then fire up the amp and check DC voltages, then replace the 1000uF cap that isn't currently installed.
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Awesome help!Replaced two capacitors values came back to spec, amp is happy and so am I.
Thanks Dana