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.
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The pot is in parallel between signal and GND, while a grid stopper is in series with the signal.
28 mA, i would stop there and examine Massimos suggestion. Then maybe add like 5R between the 10R cathode resistor and ground, to measure cathode current
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Check also that you really have plus on Rodsthingie on cathode side and minus on ground side on the 10R resistor
Thus better, isn't it?
Question: was the pot set to -infinite (fully counterclockwise / central tap to gnd) during the previuous tests? or were the RCA shortcircuited?
Question: was the pot set to -infinite (fully counterclockwise / central tap to gnd) during the previuous tests? or were the RCA shortcircuited?
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 😀