Shortly after powering on my ST120 the other day, the right channel faded out and started making a static noise, I then noticed a spark emanating rear-center of the unit and that V6 was no longer on. I immediately cut power to the amp.
After a cooldown, I powered it up again. V6 was not lit but also the preamp tubes V2 and V3 were not lit up as well. Cut power to amp.
Replaced rectifier V1 and V6 and powered up again. No power on V1, V6, V2, and V3.
I opened up the unit to check for damaged components from the spark. Noticed a cold solder joint on pin 8 of rectifier V1. Couldn't find any problem with V6 connections or any components.
Put unit back together, V1 is on but V6, V2, and V3 are off. Decided to try powering up in triode mode. All tubes light up in triode mode, but I heard a noise on the right channel increasing in frequency gradually on right channel. Cut power to amp.
I agitated the triode/pentode switch and powered up in pentode mode. Everything works great and I run the amp for a few hours.
Today, powered on amp to original issue. V6, V2, and V3 not lit up, large spark after a minute or so. Just to see what would happen, I gave the amp a bump - just picked it up from the front an inch and let it drop. Powered back up fine, and then listened to it for about 30 seconds before right channel cut out again: same tubes V6, V2, and V3.
I am ordering some new soldering iron tips tonight as my next step will definitely be fixing the cold solder joint on the rectifier.
Are there any additional connections I should check? I can't seem to find any other connection problems following the signal path to V6, and I'm unsure of how to troubleshoot V2 and V3. I'm worried if there's one cold solder joint there could be another, even though when I built things thing, I was very careful. I assembled this unit in 2021.
Thanks in advance!
-Derek
After a cooldown, I powered it up again. V6 was not lit but also the preamp tubes V2 and V3 were not lit up as well. Cut power to amp.
Replaced rectifier V1 and V6 and powered up again. No power on V1, V6, V2, and V3.
I opened up the unit to check for damaged components from the spark. Noticed a cold solder joint on pin 8 of rectifier V1. Couldn't find any problem with V6 connections or any components.
Put unit back together, V1 is on but V6, V2, and V3 are off. Decided to try powering up in triode mode. All tubes light up in triode mode, but I heard a noise on the right channel increasing in frequency gradually on right channel. Cut power to amp.
I agitated the triode/pentode switch and powered up in pentode mode. Everything works great and I run the amp for a few hours.
Today, powered on amp to original issue. V6, V2, and V3 not lit up, large spark after a minute or so. Just to see what would happen, I gave the amp a bump - just picked it up from the front an inch and let it drop. Powered back up fine, and then listened to it for about 30 seconds before right channel cut out again: same tubes V6, V2, and V3.
I am ordering some new soldering iron tips tonight as my next step will definitely be fixing the cold solder joint on the rectifier.
Are there any additional connections I should check? I can't seem to find any other connection problems following the signal path to V6, and I'm unsure of how to troubleshoot V2 and V3. I'm worried if there's one cold solder joint there could be another, even though when I built things thing, I was very careful. I assembled this unit in 2021.
Thanks in advance!
-Derek