Today, KIT kits are sold on well-known websites under the name “USB linear power amplifier 70 watts for a frequency of 3.5-30 MHz”.The power may still indicate 50 watts.I bought such a set and assembled this amplifier, and in this article I will tell you how to assemble and configure it.There is a video at the end of the article, and you can also use it to build an amplifier.
This is a push-pull amplifier, assembled on two IRF530 mosfets.The SMD components are already installed on the board.We need to wind the input and output transformers and install transistors on the heat sink, which is not included in the kit
It is necessary to squeeze out the walls for transformers on the printed circuit board.First assemble the two transformers as shown in the photo.Insert the iron tubes into the ferrites.The ends of the tubes should be soldered to the walls.Metal tubes are one of the windings of the transformer.
Solder the transformer frames to the board.Now we need to wind the windings.For the input transformer, it is necessary to wind two turns, and the output has three turns.
Then solder all the other parts.The pin of the relay must be bent.
The choke contains two turns of wire.It is possible to wind the coils with a mounting wire for convenience
The heat sink should be of normal size for better heat removal from the transistors.Transistors to the heat sink are installed with insulating gaskets through thermal paste.The transistor flange must not have electrical contact with the heat sink
Install the jumpers as shown in the photo.In this position, the relay switches its contacts and the amplifier is ready for operation.But configuration is required.It consists in setting the voltage at the gate-sources of transistors.It should be about 3.5-3.6 Volts, do not do higher, otherwise the transistors will get very hot and will not have time to dissipate heat and may fail.Apply a voltage of 13-14 Volts to the amplifier.
I connected two cables with a resistance of 50 ohms each to the input and output of the amplifier.At the input of the amplifier, I send a signal from a homemade 27 MHz transmitter, its output power is 200 mW
The output power will be about 7.3 watts, the signal amplification has occurred more than 30 times.This is very good, because you need to send a more powerful signal to the input.But we must take into account that not all frequencies will have the same gain.At a frequency of 3.5 MHz, the output power will be about 65-70 watts, at a frequency of 27 MHz it will be less.The input of the amplifier is usually supplied with a signal with a power of up to 5 watts.
