Need some help. Built your vta board, installed in in an st 70 using the instructions and pics as instructed. When I plug in and power up, the 2 outside 12AT7's get warm but don't light up. The center 12AT7 wont even get warm. I checked the voltage across the 2 wires that connect to the board from V3 and V6 and get 6.1 VAC. Where do look next?
3 posters
VTA initial start up problem
grizzinca- Posts : 40
Join date : 2011-12-31
danskman- Posts : 17
Join date : 2012-01-14
Age : 65
Location : Bière, Switzerland
Welcome aboard!
I wouldn't worry about not seeing the filament shining in the two outer 12AT7, some tubes show it, some don't, depending of their structure; if they get warm, the filament should do its work. The center tube should get warm, too. Try to cross it with another 12AT7 and check if it gets warm. If not, triple-check the diagram and the filament wiring on the VTA board, you should find the problem easily.
Good luck,
Daniel
I wouldn't worry about not seeing the filament shining in the two outer 12AT7, some tubes show it, some don't, depending of their structure; if they get warm, the filament should do its work. The center tube should get warm, too. Try to cross it with another 12AT7 and check if it gets warm. If not, triple-check the diagram and the filament wiring on the VTA board, you should find the problem easily.
Good luck,
Daniel
grizzinca- Posts : 40
Join date : 2011-12-31
Thanks Daniel. I'll start there. Hope to be up and running soon
Bob Latino- Admin
- Posts : 3276
Join date : 2008-11-26
Location : Massachusetts
grizzinca wrote:Need some help. Built your vta board, installed in in an st 70 using the instructions and pics as instructed. When I plug in and power up, the 2 outside 12AT7's get warm but don't light up. The center 12AT7 wont even get warm. I checked the voltage across the 2 wires that connect to the board from V3 and V6 and get 6.1 VAC. Where do look next?
Hi,
If you have one of the newer CCS driver boards, you have to install TWO FILAMENT JUMPER wires on the bottom of the driver board from the right side 12AU7 tube socket to the center 12AU7 socket to provide 6.3VAC for the center tube's filament. I am not sure that this is the reason why your center 12AU7 does not light up but check that you did install these two jumper wires. Without these two wires installed, the center 12AU7 will not light up.
Bob