Zeus 6C33C-B Line Driver

Harmonic amplitude v. signal level at 1 kHz.

Harmonic amplitude v. signal level at 10 kHz.

Note: Distortion levels are mostly dependant on bias current, not on B+ voltage.

Operating at a higher B+ voltage, e.g. +90 volts, does not make any substantive improvement in performance,
but does increase the power dissipation and also affects the thermal stability of the tubes when run at higher currents.

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Tests for B+ Supply Voltage / Current and Vg Bias

Harmonic Amplitude v. B+ Supply Volts at 400 mA B+ Current (E-Mu 1212M + FFT).

WITH

Vg Bias v. B+ Supply Volts to Obtain 400 mA B+ Current.

Harmonic Amplitude v. B+ Supply Current at B+ 65 Volts (E-Mu 1212M + FFT).

WITH

 

Vg Bias Voltage v. B+ Supply Current at B+ 65 Volts.

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Distortion v Load

Harmonic Amplitude v. Load (at B+ 65 Volts, I = 400 mA).

Constant input amplitude - note small variation in fundament level.

N.B. Measurements at or below -120 dB vary during testing.

Percentage THD v. Load (at B+ 65 Volts, I = 400 mA).

First Test

Q1, Q2: 6C33C-B Triodes "out of the box". B+ 60 volt supply: Bench PSU (300 mA limiting). Vg bias of -19 volts (for 250 mA supply current): Bench PSU. Heater supply 12+12 Vac 100 VA toroid underneath breadboard. T1 Input Transformer: Gardners 1 : 2+2 with Rterm: 10K T2 Output Transformer: 1+1+1+1 Quad-filar wound. Output configuration to drive: 600 ohm series, 150 ohm parallel. Bandwidth 25 Hz to 70 kHz. Noise floor at -150 dB. Test pictures are 1061 pixels wide to show detail.

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WINaudioMLS 192 kHz, 1 million point FFTs

( Note intermodulation products on 1 kHz fundament and it's harmonics.)