Making an entry-level tube amp

The circuit principle is shown in Figure 1-29. This machine uses 1/26N2 as voltage amplifier and 6P1 as power amplifier. The rated power
can reach 1. 5W. The filament is powered by DC to completely eliminate AC sound. Metal film resistors are used for the resistance and CBB capacitors are used for the coupling
capacitors. The circuit board is not designed and the circuit board is welded using the "shedding" method. There should be fewer grounding points and try to use one point .
Three tubes are needed to form a stereo mode.
    The biggest workload is the installation of the output transformer. If the workmanship is not good, the sound quality will be greatly reduced. If possible, use
a finished transformer from an old tube radio. The other one can be wound by yourself, using good silicon steel sheets and high-quality wrapping wire. The tongue width of the silicon
vanadium sheet is 12mm, and the stack thickness is 18mm. For primary use, cPO, 1 enameled wire is densely wound with 2800 turns, divided into four layers, each layer has 700 turns for cross-
connection. Note that the same end is connected to the opposite end, and no wrong connection is allowed. The secondary is densely wound with 118 turns of <pO●5 1 enameled wire
, sandwiched between the primary and the middle 6 layers and stages with insulating paper to separate the openings. The quality of the transformer wound in this way is very close to that of the original finished transformer. a. The high voltage part of the
power transformer It mainly plays the role of isolation, but it does not need to be used. It can be taken directly from the mains. However, at this time, the casing must be connected to the neutral line,
otherwise there will be a risk of electric shock.
    After all the welding is completed, the machine can be powered on and tested. First, connect the load speaker, then connect the filament power supply to warm it up for a few minutes,
and finally connect the high voltage D. As long as the components are reliable and the welding is correct, the machine will generally work normally. If so, If R1 burns out at the moment of power-on, it
is mostly caused by the charging current of C2 being too large. You should replace R1 with a higher power one and reduce C2 appropriately. capacitance