In Marzaglia last May I picked up an anonymous circuit (click to zoom):
I was intrigued by the large metallic cylinder on the octal base. Just an AC power cord, on/off switch and a BNC output(?). The cylinder carries the message seen here:
 |
| JKTO 4.0 KC |
Built in 1957 by the James Knights Company from Sandwich, Illinois. I don't know why, but I think it is amusing. It should be a 4.0 kHz (KC) oscillator, resonator, crystal and given these labels
 |
| Average Temperature 57°C, 6.3V thermostat. |
the letter "T" in JKTO stands for "Temperature". Under the external cylinder there is another metallic cylinder and a wire wound at its base:
Since it did not smell or look burned, I powered it up. The cylinder got warm (not 57°C outside) and there was no output. At one point I picked a 10 MHz signal at the BNC on the frequency counter, but it did not convince me.
So probably the JKTO is/was the crystal element of a temperature controlled oscillator. Something could be broken in the circuit even if voltages are OK. I drew the circuit around the octal base and it might look like a Colpitts oscillator.
Since I don't need a OCXO at 4000 Hz I will look inside the cylinder, in part 2.
