This is a solid state (both Ge and Si transistors) instrument made using single sided printed circuit boards.
It has very good frequency calibration and amplitude stability as the frequency is changed.
The second harmonic of a 1 kHz output is down 52 dB and from 6 kHz and up they are down more than 60 dB.
Was used in the HP 3350 Carrier Test Set (AN/USM-181 Telephone Test Set TM 11-6625-602-40) that consisted of a 3 wide Combining Case (-hp- Model 1051A or 1052A), the 204 Oscillator, a 353 Patch Panel and the 403? AC Voltmeter, HP 3553 Meter & Patch Panel??
The 204C adds a SYNC input/output so that multiple oscillators can all be set to the same or harmonically related frequencies.
There was no output when the unit was turned on to any of the frequency ranges.
By spraying the OFF-RANGE switch contacts with Radio Shack Tuner - Control Cleaner & Lubricant ( RS-64-4315) the output appeared.
The frequency accuracy and amplitude stability are very good.
The power supply is a separate assembly on the back outputting +13 and - 13 VDC.
The 204B uses the old style power cord, not the modern IEC type.
There is a version that used 4 each mercury batteries to allow floating from the AC power line.
The output is DC coupled and there is an adjustment on the back panel to zero the DC component.Source Resistance
By using a Agilnet (HP) 34401A DMM and a decade resistance box to see how the external reesistance loads down the open circuit voltage from the 204C it's output impedance can be calculated to be 636.2 Ohms. But if all the impedance values of a TS-585C/U audio output meter are used as the load for the 204C and the assumed source resistance (Rs) of the 204C adjusted for the lowest error, then the Rs value of the 204C looks like 632.5 Ohms, these two values agree within 0.58%. Excel spreadsheet with the measured and calculated results.
Output Power
This oscillator was intended for use in testing telephone type equipment where the more interesting power levels were those near the noise. The max open circuit voltage from the 204B is about 5 volts or 2.5 volts into a 600 Ohm load that's 10.4 mW. The amplitude control shows 10 MW at full scale.
So this oscillator is not suitable, as it stands, to provide a 1 Vrms sine wave into the 50 Ohm input to the FTS 4060 Cesium Beam Frequency Standard since that takes 20 milliwatts.
Manual available from: Lewis Porter
The 204C Manual is TM 11-6625-1589-15-1
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