Two Tube Superheterodyne Receiver

This was my first attempt to build a superhet receiver. I had searched the internet for some low tube count circuits, and discovered Jack Bryant’s KE4ID one tube superhet. I liked the simplicity, but his circuit lacked an IF gain stage. I decided that if I was going to build a superhet, it had to have an IF amplifier stage. So, I used Jack’s circuit as a starting point, and then added a second stage for IF amplification, and reflexed audio.

Here is the schematic:

Click for a larger View

Bottom view showing wiring:

I simplified Jack’s front end to a single tuned stage mainly due to lack of parts. Some component values were tweaked a bit. AVC was also added. Lack of a double tuned front end has caused image problems with strong local transmitters, but the addition of a bank of wave-traps when using the long wire antenna has minimized the problem.

The second stage, V2, is a reflexed IF and AF amplifier using a 6HJ8. IF regeneration was added to this stage later, after it was up and running reliably. A few points of interest, regarding this stage, follow:

I have used this receiver with both an outdoor 60 foot long, 12 foot high inverted 'L' long wire antenna as well as a 30' diameter tuned loop antenna. The loop antenna, consists of a ten turn tuned loop and a one turn pickup loop. Since the receiver's tuning capacitor has 3 gangs, I used the spare gang as the loop tuning capacitor. The loop inductance was designed to match the RF coil inductance so that they would track properly. However, I had overlooked the self-capacitance of the loop, and found it necessary to add a padder capacitor get it to track properly. Overall signal strength with the loop antenna was noticeably less than with the long wire antenna, but there was considerably less noise, and the receiver has more than enough gain to compensate. The loop directionality is a major advantage in separating multiple stations on the same frequency.

Headphones used with this set are Sony Sport Walkman MDR-W08, more sensitive than I expected them to be, and certainly adequate for the audio signal that the receiver puts out.

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This page last updated: February 3, 2023
Copyright 2009, 2023, Robert Weaver