Heathkit IG-5218 (Years)

The IG-5218 is a solid-state sine-square audio generator that Heathkit sold as a kit for lab, service, and bench work. The manual is the best surviving documentation, and it covers the machine pretty completely. Sine output runs from 1 Hz to 100 kHz, with distortion under 0.1% across 10 Hz to 100 kHz. Square waves run from 5 Hz to 100 kHz with a rise time under 50 nanoseconds. Sine amplitude is stepped from 0.003 V up to 10 V. The square wave runs in 0.1 V, 1 V, and 10 V zero-to-peak ranges into loads of 2000 Ω or higher. The two waveforms are independent - you can run them separately or at the same time, and each has its own level control.

Frequency selection is done in decades. Two switches set the first two significant figures (0-100 and 0-10, ten steps each), a 0-1 control sets the third figure, and a multiplier switch covers X1, X10, X100, and X1000. Accuracy is specified within ±5% of the first two digits. The sine side will drive high-impedance loads (10 kΩ and up) on every range, or 600 Ω up to 1 V, and there's a switchable internal 600 Ω load for that purpose. Output impedance is 600 Ω on the 1 V range and below. It rises to roughly 800-1000 Ω on the 3 V range and 0-1000 Ω on the 10 V range. A front-panel meter monitors sine output on two voltage scales plus a dB scale, and it is rated ±10% of full scale with proper termination. The circuit is a differential amplifier with a complementary-pair output, using an RC notch filter to set the oscillating frequency.

Physically it's a compact bench box: 5-1/8" high, 13-1/4" wide, 7" deep, drawing 6 watts from 105-125 VAC or 210-250 VAC at 50/60 Hz. One thing to flag for anyone using one today: the square wave output is DC-coupled. Don't feed it straight into DC circuitry without capacitive coupling, and don't short the output at full 10 V. The manual also notes that the fast rise time is rich in harmonics well into the megahertz range, so a slow scope can round off the leading edge or ring on it. That's the instrument, not the generator.

A 1979 Audio (July 1979, p.99) classified page mentions a "Heathkit IG-5218" only in passing, and the OCR is too fragmentary to tell what was actually being said. The two Audio-Express chunks (2003-2004) that surfaced under this model's name are about a different, tube-based project and don't describe this generator. The IG-5218's story rests almost entirely on its own manual. No meaningful period review of it has turned up.

Type: solid-state sine-square audio generator, kit form
Sine: 1 Hz–100 kHz, <0.1% distortion (10 Hz–100 kHz)
Square: 5 Hz–100 kHz, <50 ns rise time, 0.1/1/10 V ranges into ≥2000 Ω
Sine output: 0.003 V–10 V stepped; 600 Ω on ≤1 V ranges, higher on 3 V and 10 V
Frequency accuracy: ±5% of first two digits
Circuit: differential amplifier, complementary-pair output, RC notch filter
Power: 105–125 / 210–250 VAC, 50/60 Hz, 6 W
Dimensions: 5-1/8" H × 13-1/4" W × 7" D