Sunday, August 28, 2016

Sony TC-500 reel to reel player restoration

TC-500 is 4 track stereo reel to reel player which is build around 1960 - 1970 by Sony Corporation. This is vacuum tube base reel to reel player with 2 × 3W audio output power. TC-500 is dual speed (3¾ and 7½ ips) tape recorder and it support reels up to 7 inches (18cm). Amplifier stage of this tape recorder is build around 12AX7, 6AU6 and 6AQ5 vacuum tubes and 12BH7 tube is used in biasing oscillator. Other than above tubes, 6CA4 is used in PSU for rectification.

Restored Sony TC-500 reel to reel tape recorder.

Recently we got a chance to restore TC-500 reel to reel player which we got from one of our friend. The player which we got is heavily damaged and we spend nearly 2½ months to restore this player.

In first stage of restoration we disassemble mechanical parts of this player and clean everything. In this player capstan idler wheel and take-up idler wheel is damaged beyond repair and we reconstruct those wheels using rubber sheets.

Saturday, May 28, 2016

Modified Heathkit HD-1410 electronic keyer

HD-1410 is quiet popular iambic keyer which is manufactured around 1970's by Heathkit. The original HD-1410 keyer is designed using 5 commonly available 74LS series TTL ICs and 8 transistors. Other than iambic operation it has an option to adjust sidetone frequency and support for (external) single-paddle key unit.

In this project we redesign original HD-1410 electronic keyer with today's commonly available components. In this new design the key components which we replace are transistors, diodes and power supply section of original HD-1410 circuit. Most of the NPN transistors in original design are replaced with KSP42 and KSP10 transistors, and all the PNP transistors are replaced with KSP92 transistors. To keep everything simple we also use same TTL chip-set with this new design.

PCB of modified Heathkit HD-1410 electronic keyer.

Tested PCB layout for this new keyer is available in the project archive and this PCB layout is based on standard though hole type components. Dimensions of this PCB is 110mm × 102mm.

We test this modified HD-1410 design with several transceivers and it performs extremely well. This new design also behaves similar to original HD-1410 unit and the parameters which got change are DC input voltage range and power consumption only.

Schematic, PCB and wiring diagram of this modified HD-1410 keyer are available to download at The original Heathkit HD-1410 schematic and details are available at

Sunday, May 1, 2016

Simple crystal tester

This is simple Colpitts oscillator to test commonly available passive crystals which range between 2MHz to 27MHz. This unit must connect to an oscilloscope and/or frequency counter to get the frequency of the crystal.

This circuit is design to work around 9V to 12V DC power source. Both 2SC930 transistors can replace with any high speed NPN transistor such as 2SC829, 2SC933, etc.

Testing 5030kHz FT-243 crystal using prototype version of crystal tester.

In our lab we use Manhattan style layout to prototype this crystal tester and it produces highly accurate results with above specified frequency range. According to our observations, after 27MHz, amplitude of the waveform starts to decrease steeply.

Schematic and Stripboard wiring layout for this crystal tester is available to download in here.

Monday, April 18, 2016

USB curve tracer for NPN transistors

Curve tracer is an electronic test instrument to analyze the characteristics of transistors and other discrete semiconductors. In this post we construct USB base curve tracer to analyze properties of NPN transistors. This curve tracer is build around Microchip's PIC18F4550 MCU and it use simple Windows based GUI application to plot captured data of a transistor.

In this design PIC18F4550 MCU is used to establish USB connectivity, perform voltage readings and control current/voltage flow into the test subject. To minimize the cost and to make it simple, we use R2R ladder circuit to generate discrete collector-emitter voltage levels for the transistor on test. In each scan session collector-emitter voltage level get increase from 0V to 7.5V in 256 steps. In this design, "tracer" scans the transistor for 7 base current levels which are in between 7µA to 60µA. In viewer application collector-emitter voltage levels are plotted on x-axis and collector current is plotted on y-axis.

Results generated for 2SC945 NPN transistor.

In current firmware, PIC18F4550 communicates with the PC over USB-HID class and because of that this may not need any special device drivers on host terminal. In most of Microsoft Windows operating systems the viewer application may be able to communicate with the device directly. Viewer application bundled in this project package are developed using Microsoft .net framework and it can run immediately on any new PC with minimum amount of prerequisites. Based on our experiences the most recommended operating system for this application is either Windows 7 or Windows 10.

Results generated for 2SD400 NPN transistor.

To get the perfect results we highly recommended to construct this project on PCB. According to our experiences breadboards and veroboards may generate lot of noises and may finally leads to wrong output(s).

This is an open source hardware project and all it's design files, source codes and compiled binaries are available to download at All the content of this project are released under the terms of GNU GPL version 3.0.