Ok. Back to this set of voltages. The only other thing I can think of that matches your results is that the 3.12V cathode voltage stated here is actually for V1A? Because no voltage drop between R7 & R8 would obviously indicate near zero current. So the thing to check is the ground connection of V1B cathode.
One Bottle preamps. Strange...
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Ok. Back to this set of voltages. The only other thing I can think of that matches your results is that the 3.12V cathode voltage stated here is actually for V1A? Because no voltage drop between R7 & R8 would obviously indicate near zero current. So the thing to check is the ground connection of V1B cathode.
gemini86
Well-known member
yeah, that's what's throwing me off also. I don't see how R7 can have no drop, yet cathode R DOES? It's hard to see all the pins in the pics, maybe a couple angles would help.
Yep I know it seems kind of crazy but I'm pretty sure I'm doing it right, I don't get it, it's probably something really obvious...
I'll take more shots tomorrow and redo all measurements. Cathode voltages were almost the same for V1A and V1B.
The other thing would try is to increase R7 to see what happens...
I'll take more shots tomorrow and redo all measurements. Cathode voltages were almost the same for V1A and V1B.
The other thing would try is to increase R7 to see what happens...
Jules,
can you please check your cathode resistor on V1B ?
Though I am not sure because they don't appear clearly on the pictures you posted, looking at their colors, they seem like they are way too high (like 220k). And that would explain why you have such a low drop on R7 : with this high cathode resistor, your idle bias current will be VERY low (like 0,1mA) and R7 will drop around 1V only.
can you please check your cathode resistor on V1B ?
Though I am not sure because they don't appear clearly on the pictures you posted, looking at their colors, they seem like they are way too high (like 220k). And that would explain why you have such a low drop on R7 : with this high cathode resistor, your idle bias current will be VERY low (like 0,1mA) and R7 will drop around 1V only.
PRR thanks for the note, i'll make sure I brand it into my brain with hot iron, seems obvious though.
Eskiclown I think you spotted it! They are 220k instread of 220R (250R on schematic), I don't know how it slipped, I guess if I was more intimate with tube circuitry it would have jumped at me as I assembled it. I'll change them as soon as I can, I need a little while off the circuit to clear my head.
Thanks for your help everyone, hopefuly this is it!
jules
Eskiclown I think you spotted it! They are 220k instread of 220R (250R on schematic), I don't know how it slipped, I guess if I was more intimate with tube circuitry it would have jumped at me as I assembled it. I'll change them as soon as I can, I need a little while off the circuit to clear my head.
Thanks for your help everyone, hopefuly this is it!
jules
Ok so I was excited and pulled the thing out to do the changes.
It's much better now! The plate voltage at V1B is around 120V.
And...... 2 channels seem to oscillate as PRR mentioned. I need to move this output cap.
Seeing how they are placed, does anyone have an opinion on the new placement? Should I just turn it around and make the wiring go around along the face plate?
Thanks guys!
jules
It's much better now! The plate voltage at V1B is around 120V.
And...... 2 channels seem to oscillate as PRR mentioned. I need to move this output cap.
Seeing how they are placed, does anyone have an opinion on the new placement? Should I just turn it around and make the wiring go around along the face plate?
Thanks guys!
jules
