Vacuum Tube Amplifier 45/2A3 Compatible Single Amplifier / Output tubes included: 2A3 (Custom Built)

This is a compatible single-ended amplifier that can be used with both 45 and 2A3 tubes, created for Mercari listing. It features a simple and classic design.

■Switching between 45 and 2A3 output tubes is done simply by changing the bias resistor value.
The circuit constants were originally determined with the 45 tube as the base. Due to the capacity of the power transformer, the plate voltage and current for the 2A3 are slightly reduced. This results in a lighter operating condition for the 2A3, with a plate loss (Pd) of 11.7W out of the maximum 15W for the 2A3, achieving a 74% rating and a long lifespan design.
■There are no adjustment points as it uses self-bias and does not have a hum balancer.
■The maximum output is 2W for the 45 and 2.5W for the 2A3, both providing sufficient volume. The input sensitivity at maximum output is 650mV for the 45 and 550mV for the 2A3.
■It includes a volume control, so you can directly connect the output of a CD player, etc. However, using it with a preamplifier (line amplifier) is recommended.
■High-efficiency speakers (91dB or higher) are recommended. Compatible with 6-8Ω speakers.
■As it uses directly heated triodes, no NFB (Negative Feedback) is applied, making it a non-feedback amplifier. While not a wide-bandwidth amplifier, it offers a well-balanced sound from low to high frequencies.
■The filament of the output tubes is AC heated. Since the bias resistor is connected from the center tap (CT) of the filament winding, a hum balancer is not included. However, with both the 45 and 2A3, there is virtually no hum; the level is such that you cannot hear any hum even when pressing your ear to the speaker.
■The amplifier will be shipped with 2A3 tubes installed. If you wish to listen to the sound of the 45 tube, please purchase 45 tubes separately. The 2A3 tubes are Chinese-made; their glass bulbs appear slightly tilted, but this is not noticeable when inserted into the amplifier. Their characteristics are matched. The rectifier tube, 80, is a domestic Hitachi product, and the 6AU6 is a Matsushita (National) product.
■The speaker terminals support banana plugs, and a power cord is included.
■There is no rear cover.
■The transformer cover is a clear plastic cube placed loosely over the unit as a simple cover. It will not deform due to heat from the output tubes.
■There are slight unevennesses in the hand-painted finish on the wooden frame and chassis.
■A circuit diagram is included.
■Detailed information is also posted on my blog:
https://ameblo.jp/hirochan-amp/entry-12949508526.html

While high-end components were not used, this amplifier allows you to fully enjoy the sonic differences between the 45 and 2A3 tubes.