This is my late Father's Heathkit signal generator. It has a paper stuck over the dial and various frequency calibrations marked. I used this signal generator extensively when building my Spectrum Analyser.
Here's the inside view. It is beautifully clean inside and well constructed.
The under chassis photograph shows the extensive shielding around the oscillator section.
And here's what the oscillator section looks like with the shielding box removed (which is a little bit tricky to do!).
Here's a mostly-complete manual for the Heathkit signal generator. Click here to download it.