Yamamoto Sound Craft A-08S WE101D/104D Single Stereo Amplifier

This is a dedicated model for WE101D and WE104D, which have even lower output than the highly rated WE205D. Although the output is less than 1W, it achieves sound quality that is not inferior to the WE205D.

The WE101D flows 13.5mA at a plate voltage of about 250V, ensuring an output of about 0.6W with a load impedance of 5kΩ. The power consumption is about 3.5W. On the other hand, the WE104D is designed to achieve a maximum output of about 0.8W at a plate voltage of 190V as per specifications. In both cases, the plate current is finely adjusted by changing the cathode resistance to set it to the optimal value, achieving an output of about 0.8W as per specifications. Furthermore, by simply switching the cathode resistance, both WE101D and WE104D can be used.
The WE101D and WE104D look very similar, with almost no difference in appearance, but their characteristics and sounds are significantly different, clearly showing that they are completely different vacuum tubes. While the WE101D is characterized by a strong and energetic sound, the WE104D gives an impression of a gentle and soft sound. When comparing the two, the difference in gain is significant, so the volume position of the preamplifier needs to be adjusted considerably. Listening at the same position makes the volume difference too great, making the WE104D sound less powerful. It seems that using an output transformer of about 2.5k ohms would yield better results for the WE104D, as it appears to have slightly too little gain.

It's almost unbelievable how sensational!!
The 101D is far better than the 300B. It's the best amplifier I've ever had.
The impression of the amplifier using WE101D is that, except when producing loud volumes, it has the most dynamic and clear sound among all the amplifiers from the same company, including WE205D, 45, and 300B. This seems to be greatly influenced by the non-choke power supply of this amplifier. Normally, amplifiers use choke coils to eliminate ripple from the B power supply of the output stage, but this amplifier does not use choke coils due to its low current consumption and instead forms a filter with only CR to supply the B voltage.

The output stage's cathode bypass capacitor uses a polypropylene capacitor with a lug terminal from the American Dearborn company, which is sealed in a Bakelite case with high-strength epoxy resin, contributing significantly to the sound quality. Additionally, this unit uses a vacuum tube called Siemens C3m as the driver tube, with the shield case removed. The C3m is a relatively new design pentode released around 1968, known for its excellent characteristics, producing a clean sound with minimal noise.

Both the WE101D and WE104D tested the ST type and tennis ball type, with the ST type producing a well-defined tight sound and the tennis ball type offering a more relaxed and spacious sound. The tennis ball type is visually interesting and enjoyable to look at, but it is expensive, so I felt that the ST type would be sufficient if choosing based on sound quality. The speaker terminals only have an 8Ω output terminal, but there are no issues using 4Ω or 16Ω speakers. However, in either case, the maximum output will decrease. With a maximum output of 8W, the output will be around 4-6W.