3 candidate circuits come to mind: the Armstrong, Hartley, and Colpitts oscillators. Usually found in RF equipment, value changes (large caps.) will produce the 60 Hz. you want. Adjustable is not a problem, as that's exactly the case in superhet radio receivers.
A regulated B+ rail is an important step in controlling frequency drift.
Good luck!
A regulated B+ rail is an important step in controlling frequency drift.
Good luck!
The memories are FUZZY at best, but I do recall a code practice oscillator that used Colpitts topology. High impedance dynamic headphones did double duty, providing both the audible O/P and the inductance needed by the Colpitts circuitry.
Moving the generated tone down to 60 Hz. could easily be difficult as EC8010 indicated. Also, I can't begin to guess what the distortion pattern of that CPO is.
Moving the generated tone down to 60 Hz. could easily be difficult as EC8010 indicated. Also, I can't begin to guess what the distortion pattern of that CPO is.
Hi,
I have on my desk the Hewlett Packard 200CD oscillator. Mine uses 2 pcs. 6AU6 and 2 pcs. EL86. It is basically a Wien-bridge oscillator that is tuned using a variable air capacitor. It does anything between 5 Hz and 600 kHz, so your needs should be covered by it. It is a tube circuit to boot, Googling "HP 200CD schematic" yielded a schematic within the first few links. If you are a little dexterious, you should be able to bodge up something based on it, that suits your requirements. The fact that you don't need wide range tunability means that you can eliminate a lot of components.
A word about signal quality: when you hook up the secondary of a low voltage transformer to the input of an oscilloscope and look at the waveform, you'll notice that its cleanliness isn't particularly hard to beat...
Have fun experimenting!
Jurgen
I have on my desk the Hewlett Packard 200CD oscillator. Mine uses 2 pcs. 6AU6 and 2 pcs. EL86. It is basically a Wien-bridge oscillator that is tuned using a variable air capacitor. It does anything between 5 Hz and 600 kHz, so your needs should be covered by it. It is a tube circuit to boot, Googling "HP 200CD schematic" yielded a schematic within the first few links. If you are a little dexterious, you should be able to bodge up something based on it, that suits your requirements. The fact that you don't need wide range tunability means that you can eliminate a lot of components.
A word about signal quality: when you hook up the secondary of a low voltage transformer to the input of an oscilloscope and look at the waveform, you'll notice that its cleanliness isn't particularly hard to beat...
Have fun experimenting!
Jurgen
Aha! A turntable speed control is an entirely different matter. Then you will probably want crystal controlled accuracy. Or at least an oscillator with frequency stability.
I would then suggest a high frequency oscillator that drives a counter that feeds a ROM or lookup table that outputs to a DAC. An ARB, as they call it - arbitrary waveform generator. The ROM just has the PCM codes for a sinewave as you clock through it. Or some similar circuit.
Check out some of the new resistor controlled oscillators at www.linear.com. Interesting, but pretty high in frequency. Maybe too much adjust range. No xtal required. With an xtal, you will have discrete frequency steps.
Or perhaps, the poor man's version uses a square wave oscillator (LM555?) that feeds a string of RLC low pass filters. You can get a pretty good sinewave doing such. Doesn't have to be perfect to drive a motor, and the small frequency variations are no problem.
jh
I would then suggest a high frequency oscillator that drives a counter that feeds a ROM or lookup table that outputs to a DAC. An ARB, as they call it - arbitrary waveform generator. The ROM just has the PCM codes for a sinewave as you clock through it. Or some similar circuit.
Check out some of the new resistor controlled oscillators at www.linear.com. Interesting, but pretty high in frequency. Maybe too much adjust range. No xtal required. With an xtal, you will have discrete frequency steps.
Or perhaps, the poor man's version uses a square wave oscillator (LM555?) that feeds a string of RLC low pass filters. You can get a pretty good sinewave doing such. Doesn't have to be perfect to drive a motor, and the small frequency variations are no problem.
jh
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