Saturday, October 11, 2014

Digitally controlled 2.1 channel analog audio power amplifier

This article introduces high quality digitally controlled 2.1 channel analog audio power amplifier system. This project is mainly based on TDA7377 AF power amplifier and PIC18F452 8bit microcontroller. Basic features of this receiver are 2 × 6W + 20W audio output power, ±14dB bass and treble controls, fully configurable +35dB bass booster for sub-woofer and satellite speakers and loudness switch.

This system use commonly available electronic components and all the integrated circuits are in DIL packages. This amplifier consists with few UI elements such as 2 push buttons and 1 rotary encoder. All the menu navigation can perform through rotary encoder.

Prototype version of 2.1 channel audio power amplifier project

Entire amplifier can build on 147mm × 80mm PCB and all the PCB design files are available to download at project homepage.

This is an open hardware project and all the firmware source codes, design files are covered with Mozilla Public License version 2.0. All the above content and complete documentation is available to download at

Thursday, September 4, 2014

Trio JR-310 and TX-310 restoration project

I got Trio (now Kenwood) JR-310 and TX-310 SSB receiver and transmitter pair recently. When it comes to me both receiver and transmitter are in very bad shape and most of the PCBs and chassis are covered with dust and some of the components are very badly damaged. After examining both the chassis I decided to repair both units because of its vintage value (and also I like to try some tube base SSB receiver and transmitter pair).

Trio JR-310 is AM, SSB and CW mode HF receiver. This receiver has 3.5, 7, 14, 21, 25 and 50MHz operating bands and sensitivity is around 1µV. This receiver consists with 6 vacuum tubes, 5 transistors and 19 diodes. JR-310 which I restored is working with 110V and total power consumption is around 70W.

Bottom view of restored JR-310 receiver

TX-310 is 20W SSB transmitter and designed to match with JR-310 receiver. It is capable of LSB, USB, AM and CW transmissions in HF bands. This unit consists with 10 vacuum tubes, 5 transistors and 9 diodes. Like JR-310, this unit also working with 110V power source.

S2001 final stage vacuum tube and high voltage area of TX-310

I did restoration of above mentioned TX-310 and JR-310 step-by-step and most of the steps are listed in my pages.

Saturday, August 16, 2014

Eddystone EC10 communication receiver restoration and PSU add-in

Recently I got vintage Eddystone EC10 MK1 communication receiver from friend of mine and it is completely dead when it comes to me. EC10 MK1 is one of Eddystone's very early solid state communications receivers and it use 10 PNP Germanium transistors. This receiver cover 550 kHz to 30 MHz and come up with BFO for CW and SSB receptions.

Restored EC10 MK1 HF communication receiver

The main problems which I noticed in my EC10 is corroded wires, components and PCB. I did restoration step-by-step and most of the steps are listed in my page.

Other than repairing, this article covers details of power supply which I integrated into EC10 communication receiver. The schematics and photographs are available at the same article.

After repairing and above changes EC10 starts to work again and with some external antenna is performs quiet well. Most of the times I use this receiver to listen to 40m 4S7RS net on 7060kHz.

Sunday, August 3, 2014

Panasonic RX-5090T power amplifier repair

Panasonic RX-5090T is quiet old combo box from Matsushita Electric and its most notable feature is powerful three band SW tuner. Recently I got some RX-5090T unit and its problem is distorted audio output.

PCB and mechanical component distribution of Panasonic RX-5090T combo box

After careful examination we identify C128 (100µF / 10V) and C224 (3.3µF 25V) as defective components. In this unit, VR103/203 (20KΩ) potentiometer is also defective and because of that we got some random distortions when we try to change the volume of the receiver. To fix this issue we disassemble the potentiometer and clean it using isopropyl-alcohol (this potentiometer is not available in local market and only option is to clean it and use it again). After these two fixes receiver starts to work again.

Mainboard of Panasonic RX-5090T combo box

Schematic diagram of Panasonic RX-5090T is quiet difficult to find in the web and we share copy of it in here.