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?
4 posters
Rectifier troubleshooting
mijohn- Posts : 119
Join date : 2013-06-19
- Post n°2
Re: Rectifier troubleshooting
Double check your wiring especially the orientation of the two diodes, the ends with the silver bands are connected to pins 4 and 6.
steve46- Posts : 8
Join date : 2017-12-14
Age : 77
Location : Dallas
- Post n°3
Re: Rectifier troubleshooting
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.
New2Tubez- Posts : 184
Join date : 2018-03-20
Location : NY
- Post n°4
Re: Rectifier troubleshooting
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.
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.
steve46- Posts : 8
Join date : 2017-12-14
Age : 77
Location : Dallas
- Post n°5
Re: Rectifier troubleshooting
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.
New2Tubez- Posts : 184
Join date : 2018-03-20
Location : NY
- Post n°6
Re: Rectifier troubleshooting
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.
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.
steve46- Posts : 8
Join date : 2017-12-14
Age : 77
Location : Dallas
- Post n°8
Re: Rectifier troubleshooting
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.
Thanks for your suggestions.
Tubes4ever- Posts : 167
Join date : 2015-07-14
Location : Star, Idaho
- Post n°9
Re: Rectifier troubleshooting
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?
steve46- Posts : 8
Join date : 2017-12-14
Age : 77
Location : Dallas
- Post n°10
Re: Rectifier troubleshooting
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- Posts : 167
Join date : 2015-07-14
Location : Star, Idaho
- Post n°11
Re: Rectifier troubleshooting
Glad to hear it! We've all made similar mistakes at one point or other.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.
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