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Tektronix SG505
ultra-low distortion oscillator
Tektronix SG505

Produced from 1980 to 1993

Manuals – Specifications – Links – Pictures

The Tektronix SG505 is an ultra-low distortion oscillator plug-in for the TM500 system.

Option 01 adds an intermodulation test signal function.
Option 02 adds a fully balanced output to +28 dBm and selectable source impedance with corresponding changes to the front panel connections. It also includes Option 01.

Key Specifications

Frequency range 10 Hz to 100 kHz nom. (typ. 9 Hz to 110 kHz) in four overlapping ranges
Frequency accuracy 3% of dial reading
Output level +10 dBm to −60 dBm into 600 Ω in eight 10 dB steps, plus variable control +2.2 dB to −10 dB from calibrated position
Output impedance 600 Ω
Distortion < 0.0008% (−102 dB) from 20 Hz to 20 kHz
Sync output 200 mVRMS sine to 20 kHz, at least 120 mV @ 100 kHz; 1 kΩ source impedance
Opt. 1 Intermododulation Signal Regular output signal superimposed with 60 Hz or 250 Hz low frequency signal with 4:1 amplitude ratio.


The SG505 uses a state-variable oscillator topology employing NE5534 opamps and an N-FET (151-1021-00) based AGC. Range switches change capacitors and AGC time constants, the main dial changes the integrator resistor.

It's internally an surprisingly unremarkable device, no special tricks or selected parts (except for the AGC FET, which is probably some COTS FET selected for threshold voltage and distortion), just an ordinary SVO, some NE553x, standard attenuator and that's it.

See Also