The fexilbility and simplicity of the 650A Test Oscillator find a wide variety of uses in audio, video, rf, and alignment applications as well as laboratory wide band measurements. This instrument was designed for such applications as fast and accurate testing of filter transmission characteristics, tuned circuit response, complete receiver alignment, telephone or telegraph carrier equipment, plus video and audio amplifiers." (Hewlett-Packard, Manual 650A, 1956/1964)
BRIEF SPECS
| Frequency Range | 10 cps to 10 mc |
| Output Signal | 30 microvolts to 3 volts into 600 ohms |
| Power | 165 watts |
| Dimensions | 20-3/4" x 12-3/4" x 15" |
| Weight | 46 lbs |
| Technology | tube |
| Price (for 1965) | $ 550 |
The hp 650A test oscillator is a sine wave source up to 10MHz. Actually it contains two independent rc-tuned oscillator sections. For the three lower frequency bands it's a three triode amp with a Wien bridge and the famous lamp in feedback. On the two upper frequency bands a three stage phase-shift oscillator with diode-AVC is used. A monitoring level meter and attenuator completes the instrument. This one is built around 1960 and has the old-style brown cabinet with large hp-label. It was replaced by the transistorized 651 series oscillators in the early sixties.
The 650A was my very first piece of tube equipment. After cleaning I reworked the front panel and painted the cabinet. The hp front panels can be easily painted and the engraved letters can be refilled with black india ink. You have to have a very close look to see that the front panel is repainted, so this method is good to touch-up scratchy equipment. When using the 650A just one fear is still there: it uses a ballast tube for regulating the oscillator's heaters. Until now I was not able to locate any source for this tube (Amperite #12-4).
