Zeus 6C33C Triode SE Preamp & PP MOSFET Amp System Test

Test Configuration

Zeus System Test with 2:1 Output Transformer: 1 kHz THD at 4.1 Vac RMS into 8 ohms = 0.189%

Note: Although the overall THD is a lot higher than the mosfet version this is due to the 2nd harmonic. The third harmonic is quite close to the previous tests and the difference is because of the change in output transformer (EI 2-2/16" laminations plus a 0.15mm gap).

The setup is open on the bench and as is shown in the mute test there is a lot of pickup from the open power supplies and the computer equipment. Mounted properly on a screened chassis the majority of this will disappear.

The sound is nice and crisp with good detail. Overall the sound appears a little fuller to my ear than the mosfet version. However the sound differences are very small between the two versions and the warm triode glow may also have a subjective influence.

Test bench with hardware - with genuine warm triode glow.

SOURCE	PREAMPLIFIER	POWER AMPLIFIER	LOAD	MEASUREMENTS
PC + EMu 1212M (Balanced Output) WINaudioMLS Generator(s)			8 ohm	PC + EMu 1212M (balanced input) WINaudioMLS 1M point FFT + HP8903B
	6C33C-B Triode B+ 37 volt supply Rterm: 220K Bias: 300 mA Input Transformer: TX-102 +6dB Output TX: 1:1; 25 ohms imp.	2 x STW34NB20 mosfet V+ 34 volt supply Rterm: 120K Bias: 750 mA per mosfet Input TX: 1:10; 600 ohms Output TX: 4:1 or 2:1

Test Configuration.

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2:1 PP Gaped Output Transformer

2.1 watts = 4.08 volts into 8 ohms - 1 kHz FFT (-6dB) - 0.1306% THD

1.1 watts = 2.88 volts into 8 ohms - 19 + 20 kHz FFT (-12dB peaks) - 0.1812% IMD

MUTE = 0 volts into 8 ohms - noise, 50 Hz and harmonics, plus computer / monitor PSU >30 kHz pickup - FFT