Uploaded December 2013 | Updated September 2026, 1 week ago
Okay, so it sounds terrible. What I'm trying to do here is use two RF oscillators, one fixed, one voltage controllable (i.e. a frequency modulation oscillator), then mix the two with a 6BE6 heptode to generate the audible frequency.
The first oscillator is a simple Hartley LC oscillator. The second one is the same with a reactance tube attached to it. If you search for 'reactance tube' you will find a few example circuits.
There are many things wrong with the build. Particularly around the lower frequencies where the two oscillators tend to lock on to each other because they're not very well isolated. This makes lower frequencies look more like unstable impulse waveforms. General frequency stability is an issue too,
I'll see if I can get some low frequency crystals and make oscillators based on them. Maybe there will be more stability.
Can you guess the tune?
Okay, so it sounds terrible. What I'm trying to do here is use two RF oscillators, one fixed, one voltage controllable (i.e. a frequency modulation oscillator), then mix the two with a 6BE6 heptode to generate the audible frequency.
The first oscillator is a simple Hartley LC oscillator. The second one is the same with a reactance tube attached to it. If you search for 'reactance tube' you will find a few example circuits.
There are many things wrong with the build. Particularly around the lower frequencies where the two oscillators tend to lock on to each other because they're not very well isolated. This makes lower frequencies look more like unstable impulse waveforms. General frequency stability is an issue too,
I'll see if I can get some low frequency crystals and make oscillators based on them. Maybe there will be more stability.
Can you guess the tune?
