SG503
The Tektronix SG503 is a 250 MHz leveled sinewave generator plug-in for the TM500 system.
Nine overlapping ranges cover the frequency band from 250 kHz to 250 MHz, with an additional range reserved for a 50 kHz reference frequency.
It was primarily intended to be used as an oscilloscope calibration device for measuring bandwidths up to 250 MHz. Unlike later instruments like the SG504, it does not use a leveling head but was designed and calibrated with high quality coaxial cable (P/N 012-0482-00) to operate as a closely matched system when terminated into a 50 Ω load.
The SG503 shows the selected frequency on a 3-digit LED counter.
Key Specifications
| Frequency | 50 kHz, 250 kHz to 250 MHz in nine ranges |
|---|---|
| Frequency accuracy | Within ±0.7 of one count of the least significant displayed digit for the indicated frequency |
| Amplitude | 5 mVp-p to 5.5 Vp-p in three decade ranges (terminated into a 50 Ω load) |
| Harmonics | 2nd harmonic ≥35 dB down from fundamental, 3rd and higher harmonics ≥40 dB down |
Rear interface
The sine output, remote amplitude control input, and a 12-bit non-multiplexed BCD version of the counter value are available via the rear connector.
Internals
The SG503 uses two LC Hartley oscillators, one for 100 MHz and above with an air-core inductor, the other for the lower ranges using switched ferrite-core inductors. Tuning is accomplished via a traditional three-section variable capacitor. After filtering, a regulated power amplifier stage (caution: beryllium oxide in transistor cases!) is followed by a peak-to-peak detector for the amplitude control loop, and switchable output attenuators.
The frequency counter circuit starts with a ÷8 prescaler (SP1670 and 10131 ECL flip-flops) followed by 7490 TTL BCD counters and 7-segment decoders (display not multiplexed).
Notes
The Tek 012-0482-00 cable is made from RG-223 50 Ω double-braid shielded coaxial cable (or equivalent), and is exactly 36" from end-to-end.
Links
- SG503 @ amplifier.cd (German) including measurements of cable influence (1 m Belden H-155 as replacement for original cable)
- SG503 Peak-to-Peak detector substitute by John K. Bennett AE0AM
- SG503 Lab Check In and Calibration by Zenwizard Studios @ YouTube
- Tektronix SG503 Refresh and Alignments by Zenwizard Studios @ YouTube
Documents Referencing SG503
Prices
| Year | 1979 | 1980 |
|---|---|---|
| Catalog Price | $1,325 | $1,375 |
| In 2023 Dollars | $5,600 | $5,100 |
According to an internal memo, annual sales were estimated at 1200 units in 1979.
Pictures
Early model
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Left Internal
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Right Internal
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Attenuator Board Part
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Attenuator Board Top
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Attenuator Board Bottom
Late model
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Left Internal
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Right Internal
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Components
Some Parts Used in the SG503
| Part | Part Number(s) | Class | Description | Used in |
|---|---|---|---|---|
| 151-0614-00 | 151-0614-00 | Discrete component | Tek-made RF power transistor | SG503 |
| 155-0107-00 | 155-0107-00 | Hybrid integrated circuit | leveller | SG503 |