Simple one-valve signal generator (ECC82) - UK Vintage Radio Repair and Restoration Discussion Forum

Merlin · 10th Oct 2006, 10:20 am

This is a simple design for a signal generator using an ECC82, based on a schematic in the Radio Handbook (13th ed). I redesigned it to use standard values and altered the output design slightly.
Here's the schem:
http://i81.photobucket.com/albums/j2...e/SigGen-1.jpg
And some pics of the wave on an oscilloscope:
http://i81.photobucket.com/albums/j2...e/CIMG1364.jpg
http://i81.photobucket.com/albums/j2...e/CIMG1362.jpg
It will deliver a decent sine wave from about 100Hz to about 3kHz- (pretty much guitar range which is why I built it) at about 3V p-p. The 1M pot is the frequency control, the 100k is output level and the 4k7 pot adjusts the wave form. You'll need to adjust this quite a lot for the best shape, especially at low frequencies. I found that on one setting it's fine until you alter the frequency up or down a lot, then the circuit stops oscillating and you have to adjust it to get it going again. It's a bit like a trigger control I suppose.

The design of the power supply is not critical; it will work on anything from 150V to 200V and probably up to 250V too. I used a pair of back to back transformers and a half wave rectifier, but a full-wave would be better. Total current consumption was about 14mA, not including the heater supply of course.

It shouldn't take much imagination to design a small amplifier or buffer for the output too if you wanted. A simple triode with local feedback would be a good choice for some additional gain and low output impedance.
There probably ought to be a resistor in series with the output to prevent accidental short circuits; about 10k would do.

10th Oct 2006, 10:20 am	#1
Merlin Retired Dormant Member Join Date: Apr 2006 Location: Shrewsbury, Shropshire, UK. Posts: 67	Simple one-valve signal generator (ECC82) This is a simple design for a signal generator using an ECC82, based on a schematic in the Radio Handbook (13th ed). I redesigned it to use standard values and altered the output design slightly. Here's the schem: http://i81.photobucket.com/albums/j2...e/SigGen-1.jpg And some pics of the wave on an oscilloscope: http://i81.photobucket.com/albums/j2...e/CIMG1364.jpg http://i81.photobucket.com/albums/j2...e/CIMG1362.jpg It will deliver a decent sine wave from about 100Hz to about 3kHz- (pretty much guitar range which is why I built it) at about 3V p-p. The 1M pot is the frequency control, the 100k is output level and the 4k7 pot adjusts the wave form. You'll need to adjust this quite a lot for the best shape, especially at low frequencies. I found that on one setting it's fine until you alter the frequency up or down a lot, then the circuit stops oscillating and you have to adjust it to get it going again. It's a bit like a trigger control I suppose. The design of the power supply is not critical; it will work on anything from 150V to 200V and probably up to 250V too. I used a pair of back to back transformers and a half wave rectifier, but a full-wave would be better. Total current consumption was about 14mA, not including the heater supply of course. It shouldn't take much imagination to design a small amplifier or buffer for the output too if you wanted. A simple triode with local feedback would be a good choice for some additional gain and low output impedance. There probably ought to be a resistor in series with the output to prevent accidental short circuits; about 10k would do.