EL156 DIY Tube Amplifier - EL156 AMPLIFIER

The single-ended Class A tube amplifier made of EL156 has low cost, small size, and output power of up to 25W, making it an ideal power tube.

The attached picture shows the circuit principle of the power amplifier composed of 6n8P+EL156. All the parameters of the machine are marked on the picture, including the measured voltage of each point, etc. It is basically made according to the single-ended Class A power amplifier data recommended by the manufacturer. The circuit of this machine is simple, and the enthusiasts can basically meet the requirements as long as they solder correctly according to the picture. The picture shows the circuit of one channel, and the other channel is exactly the same. This machine adopts two-stage amplification, the pre-stage uses 6N8P in parallel, and the power amplifier stage uses EL156 tube to form a single-ended Class A amplifier circuit. Usually the pre-stage includes two stages of pre-amplification and driving to meet the driving requirements of the power amplifier. However, EL156 is a high transconductance, low gate voltage tube, so the pre-stage and driving stage can be combined into one stage. In Hi-Fi power amplifiers, the fewer the number of amplification stages, the smaller the noise and distortion of the signal during the amplification process. The preamplifier tube 6N8P is a dual three-stage tube, connected in parallel. It can also be replaced with a "small one" such as 6N6 according to personal preference, or other preamplifier tubes of personal tone preference, making the whole machine more visually personalized. Of course, the tone will also change when the tube is changed. In short, the tube amplifier is a personalized thing, and the change of tone can be done as long as it satisfies your own preferences.

The power supply is relatively simple, so I will not provide the schematic diagram of the power supply. This machine uses two power transformers, high and low voltage. One low voltage transformer provides three sets of 6N8P and EL156 filament 6.3V windings, and the other high voltage transformer provides one set of 5V filament windings and two sets of 450V/0.2A high voltage windings for the rectifier tube 5Z8, which are then filtered by two inductors and supplied to the left and right channels respectively. Sufficient filament preheating has a positive effect on the life of the electron tube, so when starting up, turn on the low voltage switch first, and then turn on the high voltage switch after the electron tube is fully preheated. The shutdown process is just the opposite.

The winding requirements for the output transformer of a single-ended Class A tube amplifier are relatively high. The 4 transformers and 2 power filter inductors on this machine of the author are all wound by a professional factory in Shenzhen. The data and winding method are provided by the author. The output transformers are made of 4-clip 3-layer and cross winding. The two output transformers are made of 96# silicon steel sheets. After testing, all indicators meet the design requirements, and the low-frequency, medium-frequency, and high-frequency square wave tests are also good.

Due to the small number of components, the machine adopts the "scaffolding welding" process. C1, C2, and C3 use the familiar red "WIMA", and C4 and C5 use metallized non-inductive polyester capacitors. The wiring, structure, and debugging of the tube amplifier are described in detail in many articles, so this article will not describe them. As long as the ground wire is properly routed, when the machine is working, the AC sound cannot be heard when the ear is close to the speaker. The author's "accounts" for listening include: a 24-bit CD player, a homemade 12-inch large box, and a bookshelf box imitated from a factory using an 8-inch Danish unit. After connecting the equipment one by one and testing the sound, personal evaluation: 1 The 2-inch big box has a shocking bass, "hammering to the heart", the mid-high frequency is balanced, real and layered, the 8-inch bookshelf box has a decent bass, and the mid-high frequency is clear and comfortable. In short, you may hear more music details that you have not heard before or have not heard clearly in this amplifier. As for more descriptions of the sweet sound, I will omit it here, because personal preferences are different. Maybe the clear layers and balanced sound that I love are what you don’t care about very much. If I say more, it will be "bragging"! So it is better for enthusiasts to imitate it and listen, compare and evaluate it yourself! I believe that the joy it brings you is beyond words.