This is the first vacuum tube amplifier I built. I started learning about the art of vacuum tube amplifier design and build in 2014. After a long process of trial and error I built “Il Primo”, which in English means “The First”. It uses EL34/6CA7 power tubes and 12AX7 as input and phase split.
Characteristics:
- Push-Pull stereo integrated amplifier
- Max Output Power 2x ~30W
- @ 1 Volt peak input signal, with 6dB global negative feedback
- @ 0.5 Volt peak input signal, with no negative feedback
- Power Stage: 2x 2 EL34/6CA7 power vacuum tubes in Push-Pull Ultra-Linear configuration and fixed bias
- Phase Split Stage: DC coupled Concertina with 12AX7 vacuum tubes
- Input Stage: 12AX7 vacuum tubes with self bias and bypass capacitor
- Class AB with 40 mA anode current bias
- Output Transformer: Custom
- Primary: 7.6K Ohm C.T., 40% screen tap
- Secondary: 4, 8, 16 Ohm
- Power Supply Unit Transformer: Custom 650V C.T. @400mA
- Global Negative Feedback: max 6dB adjustable
- THD (measured with Sovtek 12AX7 LPS + JJ EL34)
- at 1W: 0.05%
- at 5W: 0.08%
- at 10W: 0.24%
- Two only capacitors in the signal path
- 4, 8, 16 Ohm Speakers
- Input Impedance: 100K Ohm
- Output Impedance: 1.2 Ohm
- Damping Factor: 6.5
- 6 selectable input sources
- Bluetooth input
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