LUXKIT A3000

Commentary

This is a bulb-type monaural power amplifier kit that makes full use of the development of new materials such as output tubes, driver tubes, and output transformers and circuit technology that makes use of these materials.

Newly developed 3-pole output tube 8045G for large output is used for the output tube.
The output tube has a large plate electrode with a high heat radiation effect made of five layered metal plates, and an electrode structure with heat radiation fins, resulting in a plate loss of 45W.

The newly developed transformer GX100-3.6 developed for 8045G is used for the output transformer.
The GX100-3.6 uses a special winding method called クォドラファイラ winding, which is a multi-transformer technology. In this クォドラファイラ winding method, the primary winding of the transformer is divided into the plate side (first winding) and the cathode side (second winding), a bootstrap winding (third winding) and a minor NF winding (fourth winding) are provided, and these four windings are wound simultaneously.
The external appearance is inherited from OY36, but the content is to increase the handling capacity by increasing the core size and to minimize loss so that it can be taken out up to 100W even at 35 hz.

A cross-shunt push-pull circuit is used for the output circuit.
In this output circuit, the load of the upper and lower output tubes is divided into two parts, plate side and cathode side respectively, and these parts are cross-connected to each other. In this circuit, 6 dB negative feedback is applied to the output tube, which reduces strain and internal resistance and has a large effect on bare characteristics.
To realize this circuit, an output transformer with special winding method is required.

The drive stage uses a cathode follower direct-coupled circuit to keep the output impedance low and to obtain a drive voltage without waveform distortion. In addition, this stage requires 100% negative feedback, so there is little distortion and phase change, and favorable conditions for direct coupling with the output tube are also provided.
This drive stage employs 6240G, a newly developed twin 3-pole drive tube for high voltage.

Cathode follower Since the gain cannot be obtained by the direct drive circuit, the gain is supplemented by a pre-drive circuit using the same 6240G, which has a drive voltage of 200 vrms.
For the cathode of this stage, about 5 dB of minor loop negative feedback is applied from the fourth winding of the output transformer by the balance method. This improves various characteristics after the pre-drive stage.

The first stage of A3000 employs a differential amplification system using a bi-triode 12AX7 and at the same time serves as phase inversion.
The second stage, which is directly connected to the first stage plate, is also equipped with a differential amplifier. The phase inverted signal at the first stage is voltage-amplified and sent to the pre-drive stage. This configuration automatically compensates for the balance of the push-pull operation, resulting in excellent distortion factor characteristics.

The power supply circuit uses a power transformer (S-1934) with good regulation, a choke coil (C-1744) with low DC resistance, and a large electrolytic capacitor (220 μ Fx2).
Power is supplied to the output stage from a bridge rectifier circuit to minimize voltage fluctuations.

Tube kit TU3000 was sold separately.
8045Gx2, 6240Gx2, 12AU7x1, 12AX7x1.

Model Rating

* 8045G is used for the output tube.
Type	Tube bulb type monaural power amplifier kit
Continuous effective output	60W (4 Ω, 8 Ω, 16 Ω)
Total harmonic distortion factor	0.2% or Less (60W, 1 kHz) 0.05% or Less (10W, 1 kHz)
Frequency characteristic	10 Hz to 40 kHz - within 1 dB
Input Sensitivity / Impedance	About 800mV/80k Ω
Damping factor	16 (8 Ω, 1 kHz)
Residual noise	0.5 mV or less
Used vacuum tubes, etc.	Vacuum tube used : Semiconductors used : 8045Gx2 6240Gx2 12AU7x1 12AX7x1 U07Nx4 RA-1Bx4
Power consumption	150W (220W at maximum output)
External dimensions	Width 370x Height 170x Depth 240 mm
Weight	15.2kg
Sold Separately	Dedicated Tube Kit TU3000 (¥ 9,900) Assembly Manual (¥ 2,500)