• 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.

PP to PPP

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one I know

To double the power available at the output you will have to halve the impedance of the trafo's primary. Keeping the same impedance at the primary will imply in a lower output impedance (and a greater damping factor as consequence)

With two tubes parallel it's good to have them matched so they drag a same amount of current. If you use fixed bias, use one pot for each tube.
 

ray_moth

Ex-Moderator
2004-01-27 8:55 am
Jakarta
As stated by ErikdeBest, parallel tubes need half the plate load impedance, as well as double the current from the PS and they should have separate grid bias controls. I've seen some designs for parallel OP tubes that use a small resistor (100 ohm or so) connected in series in each plate circuit, to minimize current-hogging.

Drive signal voltage remains the same, of course, but drive current is doubled, since the OP tube grids are in parallel, grid resistance is halved and Miller capacitance is doubled. This is likely to be more of a concern if the OP tubes are triodes.
 
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