I dont understand why current goes up like this. Your one channel audio circuit now takes 115/8200=14 mA at plate voltage 120,5. Try half the resistor again.
Then we might have to have a more detailed look on your cathode and grid circuit. I'm gonna be on the road in a while but adjust last R until you goal which should be around 150 V, then you can set scope on the anode (scope on AC-mode) and measure your ripple. Then try a squarewave thru the circuit.
Aim a bit high on B+ voltage or adjust with both channels hot, cause your trafo is going to deliver less voltage with both channels current plugged in.
Then we might have to have a more detailed look on your cathode and grid circuit. I'm gonna be on the road in a while but adjust last R until you goal which should be around 150 V, then you can set scope on the anode (scope on AC-mode) and measure your ripple. Then try a squarewave thru the circuit.
Aim a bit high on B+ voltage or adjust with both channels hot, cause your trafo is going to deliver less voltage with both channels current plugged in.
Last edited:
Cathode is the tube pin where is connected the 10R? DVM plus lead to cathode where is connecte 10R & DVM minus lead to gnd reads +9,59V
Looks good. 136V on plate, 9.59V on cathode is basically the same working point as per Andy's schem (138 and 10).
Add a second grid stopper (resistor body as close to the socket pin as possible) ad fire it up!
If online newspaper won't report as breaking news a big mushroom cloud over Catalonia in the next ten minutes, means that you can check your preamp with the oscope
Add a second grid stopper (resistor body as close to the socket pin as possible) ad fire it up!
If online newspaper won't report as breaking news a big mushroom cloud over Catalonia in the next ten minutes, means that you can check your preamp with the oscope