![af filter superhet af filter superhet](https://i1.wp.com/robs-blog.net/wp-content/uploads/2020/04/IMG_20200411_103907-scaled.jpg)
So range of tuning is just about perfect, but to be properly aligned the oscillator should adjusted for about 986kHz at the bottom end of the tuning range. By contrast the AM band extends from 531 to 1611 kHz, a spread of 1080kHz. This gives an 1100kHz tuning range from 445kHz to about 1545kHz (using a 455kHz IF frequency). With the tuning capacitor at maximum capacitance it oscillates at ~900kHz and at minimum capacitance at about ~2MHz. The bias voltage circuit required by the oscillator and other sections was also built.Īfter swapping connections on the oscillator can, the oscillator leapt into life. It seemed logical to start by constructing the local oscillator since it can be tested in isolation. So it may be that the sensitivity can be improved even further.
![af filter superhet af filter superhet](http://www.armyradio.wiki/lib/exe/fetch.php?media=images:e-613-hallicrafters-sx25-back.jpg)
I’ve peaked the IF stages but haven’t yet aligned the local oscillator and tuning.
![af filter superhet af filter superhet](https://3.bp.blogspot.com/-dlEwFuUK23g/UG7SNBBRShI/AAAAAAAAAiQ/3TF3lPIzSeg/s320/1ham.png)
The selectivity is excellent, as you’d expect from a superhet. It pulls all the local stations at good volume and with good quality. The changes are required because the tuning capacitor gangs share a common ground and because the pinouts of the oscillator and IF coils differ to those specified in the design. I have drawn up a schematic with the circuit changes required to make the receiver work with these parts. This post is aimed at those who want to build the receiver using these easily obtainable parts in Australia. The radio is built entirely out out parts from my junkbox and a ferrite antenna LF1020, tuning capacitor (polyvaricon) RV5728, and oscillator and IF coils LF1050 from Jaycar. The main reason for the change was that I did not have the audio transformers required for the original design on hand. In reality, my version is a 4 transistor radio since I’ve used an audio amplifier chip in place of the 4 transistor amplifer used in the original design. This post documents my build of the 8 transistor AM superhetrodyne receiver featured in Ronald Quan’s excellent book Build Your Own Transistor Radios.