Vacuum Tube Amplifier / 12AU7 Preamp (Line Amp) / Handmade / Includes Spare Tube

This is a preamplifier (line control amplifier) using a 12AU7, designed for a vacuum tube power amplifier.
It uses only one 12AU7 tube with a very simple circuit where each 1/2 unit is assigned to the left and right channels. While the tone control circuit is omitted, it delivers a powerful sound with a balanced response from low to high frequencies.
■ The 12AU7 is used as the reference tube, but as a compatible amplifier, other tubes such as 5814, 5963, 12AX7, 5965, 12AT7, 6201, 12R-LL3, and 12AV7 can be directly swapped in.
■ The dimensions are compact: 120mm (height) x 200mm (width) x 250mm (depth).
■ There are two input terminals (CD, AUX), totaling 3 inputs. For the AUX input, an additional terminal has been added with slightly reduced input sensitivity via a resistor, which is convenient for signals with higher input voltage.
■ A phono equalizer amplifier is required for playing LP records.
■ There are some unevenness in the repainted case.
■ The fuse holder cover is missing.
■ A spare 5963 tube is included.
■ Operation of 12AU7 (1/2)
・Ep: 67.5V ・Ip: 1.56mA ・-Eg: -2.5V
■ Input/Output Characteristics
・Maximum Output Voltage: 34V / Input 5V

This compatible amplifier allows for direct swapping of many tubes. Below are the operating data for tubes other than 12AU7 as a reference when swapped.
■12AX7
・Ep: 119V ・Ip: 0.59mA ・-Eg: -0.95V
■5963
・Ep: 57.0V ・Ip: 1.75mA ・-Eg: -2.8V
■5965
・Ep: 78.0V ・Ip: 1.31mA ・-Eg: -1.45V
■12AT7 (6201)
・Ep: 104V ・Ip: 0.91mA ・-Eg: -2.5V
■12R-LL3
・Ep: 78.0V ・Ip: 1.30mA ・-Eg: -2.1V
■12AV7
・Ep: 86.0V ・Ip: 1.25mA ・-Eg: -2.0V

Oscilloscope observations of waveforms at an output voltage of 5V for 100Hz, 1kHz, and 10kHz square waves show a straightforward waveform for such a simple circuit.
For more details, please refer to the blog post:
https://ameblo.jp/hirochan-amp/entry-12960425605.html