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RE: Can I use a resistor instead of the choke for coupling to the 813?

Vinnie,
You have to know the operating points you want to run the power half of the 6EM7 in order to figure out what you need as a decoupler. For example lets say you want to run 150Vs from plate to cathode, which is straight off the RCA data sheet. Grid bias is -20V below cathode, plate current (also straight off the data sheet) is 50mA.

50mA running thought that big 8K2 cathode puts to top of the cathode resistor at 410Vs, which is kind of a non-starter. That resistor is dissipating 20Ws so your 10W is not a good idea either. So basically you need to trim down that 6EM7 cathode resistor to where the voltage on top of the cathode resistor, plus the 150 plate to cathode voltage is below B+. Then use ohms law to figure out what size of decoupling resistor you need to get from B+to the plate voltage you need.
Matt


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