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    Rectifier troubleshooting

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    steve46

    Posts : 5
    Join date : 2017-12-14

    Rectifier troubleshooting Empty Rectifier troubleshooting

    Post by steve46 on Sat Mar 23, 2019 5:49 pm

    I just completed the yellow-sheet mod on my ST-70. Now, no sound, and the rec tube isn't heating up. I've already checked for cold solder joints. Can I assume the tube has gone south and I need to order a new one? Or would a failed tube still "light up"? The amp was working perfectly before I "improved" it. All other tubes look fine. Should I revert the diode mod and then see if it will work?
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    mijohn

    Posts : 73
    Join date : 2013-06-19

    Rectifier troubleshooting Empty Re: Rectifier troubleshooting

    Post by mijohn on Sat Mar 23, 2019 7:15 pm

    Double check your wiring especially the orientation of the two diodes, the ends with the silver bands are connected to pins 4 and 6.
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    steve46

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    Rectifier troubleshooting Empty Re: Rectifier troubleshooting

    Post by steve46 on Sat Mar 23, 2019 7:34 pm

    I'm sure the orientation is correct. Not as sure of my soldering technique. My eyes aren't as good as when I originally built it. I'll have another go at it.
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    New2Tubez

    Posts : 57
    Join date : 2018-03-20
    Location : NY

    Rectifier troubleshooting Empty Re: Rectifier troubleshooting

    Post by New2Tubez on Sat Mar 23, 2019 10:39 pm

    Another thought-
    Aren't those diodes sensitive to being overheated during soldering? Did you test them? I did mine but don't recall the right number but I got it off the interweb. I was worried that I may have fried mine.
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    steve46

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    Post by steve46 on Sat Mar 23, 2019 10:49 pm

    If they're subject to get overheated, that might be my problem. I cut the leads fairly short and got them pretty hot, I imagine. I will try to test them tomorrow, or maybe just replace them. Thanks.
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    New2Tubez

    Posts : 57
    Join date : 2018-03-20
    Location : NY

    Rectifier troubleshooting Empty Re: Rectifier troubleshooting

    Post by New2Tubez on Sat Mar 23, 2019 11:32 pm

    I think I found it here:

    https://www.youtube.com/watch?v=gzh8ICLMXzQ

    I did test in circuit btw. If I did this wrong, someone let me know but they're working.
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    mijohn

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    Rectifier troubleshooting Empty Re: Rectifier troubleshooting

    Post by mijohn on Sun Mar 24, 2019 4:01 am

    This video is also very helpful for testing diodes.

    https://www.youtube.com/watch?v=BXOS5czCb3Q
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    steve46

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    Join date : 2017-12-14

    Rectifier troubleshooting Empty Re: Rectifier troubleshooting

    Post by steve46 on Sun Mar 24, 2019 12:13 pm

    Thanks for the links on diode testing. I tested them, and both are good. Next, I jumped accross the two diodes and turned on the power -- the tube lit up. I have isolated the culprit connection and tried reflowing the solder, but still not working. Now I know the tube is probabley alright, and where the problem lies. Hopefully I'll be back in business later today.

    Thanks for your suggestions.
    Tubes4ever
    Tubes4ever

    Posts : 135
    Join date : 2015-07-14
    Location : Star, Idaho

    Rectifier troubleshooting Empty Re: Rectifier troubleshooting

    Post by Tubes4ever on Sun Mar 24, 2019 10:30 pm

    The diodes shouldn't have any effect on whether the tube lights up. Are you sure you have the diodes hooked to pins 4 and 6 and not 2 and 8?
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    steve46

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    Rectifier troubleshooting Empty Re: Rectifier troubleshooting

    Post by steve46 on Sun Mar 24, 2019 10:59 pm

    You are exactly right. I hate to admit I was was working on the wrong pins. I have no "red leads" as shown on the yellow-sheet (they're all four white). I was so certain I was working on the correct pins but when I realized my mistake I corrected the wiring with no issues whatsover. Embarrassed but pleased to get the problem resolved.
    Tubes4ever
    Tubes4ever

    Posts : 135
    Join date : 2015-07-14
    Location : Star, Idaho

    Rectifier troubleshooting Empty Re: Rectifier troubleshooting

    Post by Tubes4ever on Sun Mar 24, 2019 11:04 pm

    steve46 wrote:You are exactly right. I hate to admit I was was working on the wrong pins. I have no "red leads" as shown on the yellow-sheet (they're all four white). I was so certain I was working on the correct pins but when I realized my mistake I corrected the wiring with no issues whatsover. Embarrassed but pleased to get the problem resolved.
    Glad to hear it! We've all made similar mistakes at one point or other.

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