With a small Realistic tweeter replacing the failed bulb (that supplies a Positive Temp Coefficient resistance for amplitude stability normally), it still gives a very pure sine of 878Hz or so with a no 2nd order harmonic at 928mV pp, but a fraction off distortion and lost signal at +/-10.6V DC:
Depending on voltage and resistor setting, THD is:
The next build is about the most basic you can get, but works great!:
is this build (I used a 15k not 12k):
gives a nice sine at 1000 Hz, but with 3rd order harmonics at 2Vpp - still good!:
F = 1/ 2 Pi RC
100nF = 0.1uF = 0.0000001F
1/2 Pi x 1000 Ohms x 0.0000001F = 1 /- 6.28 x 0.0001 = 1591.5 Hz