Single ended Class A pentode tube amplifier using 408A tubes.
HA-02 is the headphone amplifier which uses a vacuum tube as an amplification element. Although output power is small, it has the output terminal for speakers and it can also sound a speaker with small volume as BGM.
Only one right and left are using each the miniature vacuum tube 408A of a Western Electric for an amplification tube. Although this WE408A is a vacuum tube of a vintage, it is one of the produced vacuum tubes, and since it was used abundantly for telefon equipment, there are no worries about a spare tube even now. It seems that it was used for various uses in order to often tend to use characteristics, although this vacuum tube is originally designed as an object for high frequency amplification. When it was used for the data of a Western Electric as a small output tube, there was description that about 300mW output power was obtained. When we manufactured the amplifier for headphone based on this description, we decided to produce commercially, since the good result was obtained. (...)
HA-02 specifications: Use vacuum tube: Only WE408A 2 tubes / Circuit system: Single stage amplification, pentode connection, and non-feedback system / Maximum output : 300mW (at the time of 50ohm load) of headphone terminals, 240mW (at the time of 8-ohm load) of speaker terminals/ Frequency characteristic: 30-21,000Hz (headphone terminal) 45-17,000Hz (speaker terminal) / Gain: Headphone output power 9.5dB (at the time of 50-ohm load) Speaker output power: 1.5dB (at time of 8-ohm load) / Remains noise: 100 microvolts of headphone output power 70 microvolts of speaker output power / Outside dimension: 150 (W) 325 (D) 125 (H) / Weight: 3.5kg