Hi! I am building a dac tube output stage designed by A. Ciuffoli. This design draws about 10W per channel with 270V power supply, and output impedance is lower than 60ohms. As i mentioned this is an output stage so i dont need such low output impedance. I changed power supply to 150V (because it is shunt regulated) and changed the plate resistors. The tube is at the same operating point with both power supplies (135V, 2.75mA). With 150V power consumption is about 2.5W and output impedance is 150ohms. Circuit is tested in multisim and work fine in theory. Do you think those changes are worth it? Isn't the plate resistor value too low? Any advice is appreciated. I attached 270V and 150V schematic
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The plate resistor is way too low , that unhappy ECC83 will produce some serious distortions 
Even the original 50K is very low , of course he done some compromises to bias the transistors .
I'm not sure if an ECC83 can drive the input capacitance of the MOSFET
The ECC83 is a max 1,2mA tube so the current must be lower than that ... per triode of course , not total
Even the original 50K is very low , of course he done some compromises to bias the transistors .
I'm not sure if an ECC83 can drive the input capacitance of the MOSFET
The ECC83 is a max 1,2mA tube so the current must be lower than that ... per triode of course , not total
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I don't know what was the purpose of the original design of this output stage, but looking at it I see:
- a too low load for the tube;
- not the tube I'd use for the purpose (sticking on the 12A?7 family, a 12AT7 would be better IMO);
- not the Mosfet I'd use for the purpose (too high capacitances);
- the lack of a trimmer on the cathodes of the two triodes to balance them;
- etc...
If you give us some more details on the swing you get on the input of the triodes and what you want at their output, we can give you more details on how to reach it.
- a too low load for the tube;
- not the tube I'd use for the purpose (sticking on the 12A?7 family, a 12AT7 would be better IMO);
- not the Mosfet I'd use for the purpose (too high capacitances);
- the lack of a trimmer on the cathodes of the two triodes to balance them;
- etc...
If you give us some more details on the swing you get on the input of the triodes and what you want at their output, we can give you more details on how to reach it.
Dac output voltage is 1.2Vrms. I need to have 2Vrms on the output. And design must be balanced. I am using tubes only because of tube sound and a bit higher voltage output. Also i need output impedance lower than 200ohms. It should be a simple dac output stage. Power supply is not a problem, i can make a good one for every voltage needed.