Did the cap upgrade and now I get no sound, and I cant BIAS the tubes. What the heck did I do wrong. All tubes light up and no blown fuses. No magic smoke either upon power up. Nothing looks out of place as far as I can see. All wires look to be connected. Using the cap upgrade kit from Bob. Help PLEASE
3 posters
Upgraded caps and now no sound on St120
eminence1963- Posts : 21
Join date : 2019-06-10
Age : 60
rayton- Posts : 7
Join date : 2015-10-12
Maybe check ground of input/output
Bob Latino- Admin
- Posts : 3263
Join date : 2008-11-26
Location : Massachusetts
eminence1963 wrote:Did the cap upgrade and now I get no sound, and I cant BIAS the tubes. What the heck did I do wrong. All tubes light up and no blown fuses. No magic smoke either upon power up. Nothing looks out of place as far as I can see. All wires look to be connected. Using the cap upgrade kit from Bob. Help PLEASE
It could be just a coincidence that your rectifier "died" at the same time you did the swap to the upgraded caps.. With the amp ON, check the DC voltage from pin #8 of the rectifier tube socket to chassis ground. On a VTA ST-120 you should get 485 to 515 VDC. If you get no voltage here, the rectifier is not working. Note that just because the rectifier tube "lights up" is no guarantee that this rectifier is good. Try a different rectifier tube and see what happens ?
Bob
eminence1963- Posts : 21
Join date : 2019-06-10
Age : 60
You are right Bob the rectifier tube is not working. I plugged the unit back in with a dummy load attached and no tubes installed minus the rectifier tube installed and tube does not light up. I have to order some and get back with you when they come in. Who knows how long that's gonna be though with the world being upside down.Bob Latino wrote:eminence1963 wrote:Did the cap upgrade and now I get no sound, and I cant BIAS the tubes. What the heck did I do wrong. All tubes light up and no blown fuses. No magic smoke either upon power up. Nothing looks out of place as far as I can see. All wires look to be connected. Using the cap upgrade kit from Bob. Help PLEASE
It could be just a coincidence that your rectifier "died" at the same time you did the swap to the upgraded caps.. With the amp ON, check the DC voltage from pin #8 of the rectifier tube socket to chassis ground. On a VTA ST-120 you should get 485 to 515 VDC. If you get no voltage here, the rectifier is not working. Note that just because the rectifier tube "lights up" is no guarantee that this rectifier is good. Try a different rectifier tube and see what happens ?
Bob
Bob if you are reading this, can you answer another question? When I plug the meter its a Fluke into the BIAS points with power off not plugged into the wall outlet no tubes installed the meter shows continuity is this correct? I am a newbe to all this. So please bear with me on the stupid questions. Just trying to be safe, as I know there are lethal voltages lurking underneath the panel. Thank you for your responses.
Bob Latino- Admin
- Posts : 3263
Join date : 2008-11-26
Location : Massachusetts
Bob if you are reading this, can you answer another question? When I plug the meter its a Fluke into the BIAS points with power off not plugged into the wall outlet no tubes installed the meter shows continuity is this correct? I am a newbe to all this. So please bear with me on the stupid questions. Just trying to be safe, as I know there are lethal voltages lurking underneath the panel. Thank you for your responses.[/quote]
Yes - with the amp off your meter will show continuity through the 10 ohm 2 watt resistor on that socket to chassis ground.
Bob
Yes - with the amp off your meter will show continuity through the 10 ohm 2 watt resistor on that socket to chassis ground.
Bob
eminence1963- Posts : 21
Join date : 2019-06-10
Age : 60
Got it thanks
eminence1963- Posts : 21
Join date : 2019-06-10
Age : 60
Thank You Bob replace rectifier tube and amp is now making music once again. I was sweating that I screwed something up.
Bob Latino- Admin
- Posts : 3263
Join date : 2008-11-26
Location : Massachusetts
eminence1963 wrote:Thank You Bob replace rectifier tube and amp is now making music once again. I was sweating that I screwed something up.
Glad to hear that you are up and running again ..
Bob
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