• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Setting Pentode Screen Grid Voltage

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dshortt9

dshortt9

Member
Joined 2001
I am designing a push-pull tube amp and trying to decide whether to set the screen grids at 300v. or at the plate voltage of 550. KT-90's for tubes so the screens would be 100 volts below the 650 volt max.
What are the tradeoffs as far as power, distortion, Rp, drive voltage, etc?
 
7N7

7N7

Member
Joined 2003
dshortt9 said:
I am designing a push-pull tube amp and trying to decide whether to set the screen grids at 300v. or at the plate voltage of 550. KT-90's for tubes so the screens would be 100 volts below the 650 volt max.
What are the tradeoffs as far as power, distortion, Rp, drive voltage, etc?
Click to expand...

No experience with beam tetrode output stages, but remember the current that these valves pass is completely dictated by the screen grid voltage - hence the flat curves: varying the anode voltage makes no difference.

If I were you I would try to obtain curves for various g2 voltages and select your operaitng points accordingly.

Your valves wil pass a lot more current with 550V on g2 - and you must also be careful not to exceed the maximum screen grid dissipation (Pg2)

7N7
 
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