Yamamoto Sound Craft
A-08S WE101D/104D Single power amp

It is a sister amplifier of A-08S for exclusive use of WE101D and WE104D whose output is smaller than WE205D which has been highly evaluated.The output is less than 1W, but the sound is as good as WE205D. At the prototype stage, it was commercialized because it had sound quality that exceeded expectations and sufficient output to withstand practical use.
WE101D's low output of about 0.25W is loaded with about 250V as plate voltage, and 13.5mA is passed to make the power consumption about 3.5W.At this time, the load impedance is 5k ohm, and the output of about 0.6W is obtained.On the other hand, since the maximum output of WE104D is about 0.8W at a plate voltage of 190V, the same state is used.For both types, the plate current value is obtained by finely adjusting the cathode resistance to obtain the optimum value, and the output is about 0.8 W as specified.Also, both vacuum tubes can be used simply by switching the cathode resistance.

WE101D and WE104D are very similar in appearance, but their characteristics and sound are very different, and you can see that they are vacuum tubes with completely different personalities.Compared to WE101D, which features a powerful and energetic sound like masculine, WE104D has the impression of a feminine, gentle and soft sound.When comparing the two, the position of the preamplifier's volume must be changed significantly due to the large gain difference.If you listen at the same position, the volume will be too different and the WE104D will sound like it's not powerful.As an impression, WE104D has too little gain, so it seems better to use 2.5k ohms for the output transformer.

Item	WE101D(ST)	WE101D(Ball)	WE104D(ST)	WE104D(Ball)
Heater voltage	4.5VDC	4.5V DC	4.5V DC	4.5V DC
Plate-cathode voltage	253V	251V	189V	199V
Plate load impedance	5k ohm	5k ohm	5k ohm	5k ohm
Cathode resistance	2kohm	2kohm	3.5kohm	3.5kohm
Cathode voltage (bias voltage)	-27V	-27V	-58V	-58V
Plate current	13.5mA	13.5mA	16.7mA	16.0mA
Maximum output(THD:10%)	0.69W	0.63W	0.94W	0.81W
Gain	21.9dB	21.5dB	15.3dB	15.8dB
Residual noise	0.62mV,0.82mV	0.44mV,0.91mV	0.44mV,0.63mV	0.44mV,0.62mV
Frequency characteristic(-3dB)	21-27,000Hz	22-29,000Hz	12.6-38,000Hz	12.6-39,000Hz

The impression of the amplifier using WE101D was the most dynamic and clear sound of all the amplifiers such as WE205D, 45, 300B of Yamamoto Sound except when the volume was high.This seems to be greatly influenced by the non-choke power supply of this amplifier.A normal amplifier uses a choke coil to eliminate the ripple of the B power supply in the output stage.This amplifier uses a small choke coil because it uses a small amount of current, and forms a filter only with CR to supply B voltage.

For the output stage cathode bypass capacitor, the use of a type of Derborn lug terminal type polypropylene capacitor sealed in a bakelite case with high-strength epoxy resin also greatly contributes to sound quality.In addition, this machine uses a Siemens C3m vacuum tube as the driver tube with the shield case removed.C3m is a relatively new pentode that was released around 1968. It is an excellent vacuum tube with very good characteristics, clean sound and little noise.


Both WE101D and WE104D tested the ST type and the ball type, but I felt the ST type was a good tight sound, and the ball type was a rough and spacious sound. The ball type is interesting to see and fun, but since it is expensive, I felt that the ST type would be sufficient if it was selected from the sound quality.

Vacuum tubes	WE-101D/104D*, C3m,80
Maximum output	WE101D:0.6W/8 ohms WE104D:0.8W/8 ohms
Frequency response	22Hz-28kHz(-3dB)
Output transformer impedance	Primary side 5k ohms, Secondary side: 8 ohms
Residual noise	0.4-0.8mV
Drive system	CR coupling, self-bias method
Dimensions	400(W)294(D)204(H)m
Weight	14.3 s

*Since vacuum tubes are rare and difficult to obtain, please contact us if you wish to have an output tube. For reference, the WE101D ST type pair costs around 80,000 yen.
**Since it will be made to order, the delivery time may take more than 3-4 months.