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In the Forum: Melquiades Amplifier
In the Thread: To drive the 6C33C...
Post Subject: operating pointsPosted by guy sergeant on: 3/20/2006
Melquiades condition (both cathodes heated)

Plate Voltage 220v
Bias Voltage -80v (-110v puts the working point in a ridiculous place on the curves I have)
Plate current (according to the curves) 165mA approx
Power Output 15.5 Watts
2nd Harmonic Distortion 14.8% (hmm, nice)
3rd Harmonic Distortion 2.8%
4th Harmonic Distortion 2.1%
THD 19.7% (approx)

Another Condition

Plate Voltage 143v
Bias Voltage -40v
Plate Current 336mA !
Power Output 5.5 Watts
2nd Harmonic Distortion 2.3%
3rd Harmonic Distortion 0.5%
4th Harmonic Distortion 1.2%
THD 4% (still a bit high)

I must be missing something because I normally wouldn't bother trying to make an amplifier with this type of power supply regulator valve. The advantage (if there is one) must lie in the output transformer design ie less of a step down ratio than with the higher impedance valves.

I have not built or heard one of these amplifiers yet so would reserve judgement on how well it works. I am interested to try but I'd like an explanation for how the 6C33C can sound good when it behaves like this. It goes against my 'limited' understanding.

best regards,



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