Servicing Heathkit IO-12 Oscilloscope

Few months back I got an old Heathkit IO-12 Oscilloscope from my friend and at the time of delivery this unit is not under the working conditions. Heathkit IO-12 is Value based laboratory oscilloscope with following technical features,

Frequency Response : 3Hz to 4MHz ≅ 5MHz
Sensitivity : 0.025V/inch
Rise time: 8µS
Sweep Range : 10Hz to 500kHz

When I remove the casing of the oscilloscope I found several damaged components (specially capacitors) and wires. After making the careful observation and testings I decided to rewire the whole oscilloscope with new components except the following,

12BH7 Dual Triode
12AU7 Dual Triode
6AN8 Triode Pentode
6AB4 Triode
1V2 ½ Wave Rectifier
6X4 Full Wave Rectifier
6J6 Dual Triode

Main Transformer
Front end controls (including switches, potentiometers, connectors and indicator)
Most of the inductors
Cathode Ray Tube, etc

As mentioned in the above list all the Values, transformers and some of the critical components are in good condition. Only the major problem occurs at the electrolytic capacitor replacement stage(s) because in original configuration there are two capacitors packs (4 Pin capacitor package with common ground) are available. It is bit difficult to obtain those capacitors from local market. So what I'm doing is installing 4 separate electrolytic capacitors, instead of one single electrolytic capacitor pack. To do this I'm slightly change existing component layout of the original IO-12 Oscilloscope. Except these capacitor modules all other parts are commonly available in local market. (with some slight differences in packages and values)

After the rewiring, this unit work nicely and produce results as same as today's professional analog oscilloscope. At the time of testing I couple this unit with one of my old Phillips GM4585 trigger delay unit and achieve successful results. The above photograph indicate this restored IO-12 oscilloscope with 50Hz - 12.75V peak to peak sine wave.

Comments

CD2003 - yet another simple FM radio receiver

In the last few days, we are looking for some simple FM radio receiver to integrate into one of our ongoing projects. For that, we try several FM radio receiver ICs including TDA7000, CD2003/TA2003/TA8164, CXA1019, and KA22429. Out of all those chips we select CD2003 (or TA2003/TA8164) based receiver for our project because of its simplicity and outstanding performance. Except to CD2003, Sony CXA1019 also perform well but we drop it because of its higher component count. We design our receiver based on Toshiba TA2003 datasheet and later we try TA8164 and CD2003 with the same circuit. Either CD2003 or TA8164 can directly replace TA2003 IC, and as per our observations, TA8164 gives excellent results out of those 3 chips. A prototype version of CD2003 FM radio receiver The PCB design and schematic which we used in our prototype project are available to download at google drive (including pin-outs of crystal filters and inductors ). Except for CD2003 IC, this receiver consist...

Arduino superheterodyne receiver

In this project, we extend the shortwave superheterodyne receiver we developed a few years ago . Like the previous design, this receiver operates on the traditional superheterodyne principle. In this upgrade, we enhanced the local oscillator with Si5351 clock generator module and Arduino control circuit. Compared to the old design, this new receiver uses an improved version of an intermediate frequency amplifier with 3 I.F transformers. In this new design, we divide this receiver into several blocks, which include, mixer with a detector, a local oscillator, and an I.F amplifier. The I.F amplifier builds into one PCB. The filter stage, mixer, and detector stages place in another PCB. Prototype version of 455kHz I.F amplifier. In this prototype build, the Si5351 clock generator drives using an Arduino Uno board. With the given sketch, the user can tune and switch the shortwave meter bands using a rotary encoder. The supplied sketch support clock generation from 5205kHz (tuner f...

Calculator for audio output transformers

Audio output transformers are heavily used in a vacuum tube and some (older) transistor base audio power amplifiers, but these days output transformer are quite hard to find and expensive item. For homebrew projects, the best option is to construct those transformers by ourselves and this script helps to calculate winding parameters for those transformers. This " AF output transformer calculator " script is written using Python and it works with most of the commonly available Python interpreters . The script is available to download at google drive under the terms of GNU General Public License version 3.0 . Homebrewed 25k: 4 output transformer Once supplied the input parameters this script provides a winding ratio, the number of turns required for primary and secondary winding and required copper wire gauges for both primary and secondary windings, etc. We construct several AF output transformers based on results of this script, which including transformers for M...