Product Overview
Heathkit IN-37 Decade Resistance Substitution Box - 15Ω to 10MΩ, 1W, 500V, Shorting Switches, Tested Working
Condition
Single unit available. Used, with normal wear - light scuffs, surface scratches, and dust consistent with bench use. Panel lettering crisp and legible, both selector knobs intact, HI/LO toggle switch functional, and binding posts present. Interior phenolic wafer assemblies show age patina on solder joints; all joints intact. Black enclosure has moderate surface scratching on the lid. Tested and confirmed functional. Series No. 014 1321 and 814 1621 labels both readable on chassis.
Carefully packed and shipped same business day from our Idaho warehouse. Online since 1999. Honest equipment and straightforward service.
No hassle resolution if there is an issue. Serving customers since 1999.
Product Overview
Heathkit Model IN-37 is a passive resistance substitution box covering 15 ohms to 10 megohms. It uses two rotary selector switches with make-before-break (shorting type) action and a HI/LO range toggle to dial in resistance values across the full range. Resistors are rated 1 watt at continuous operating voltages up to 500V. The unit connects directly to a circuit under test via two binding posts - no power supply required. Heathkit produced several resistance substitution models; the IN-37 is distinguished by its 15Ω-10MΩ range and dual-wafer rotary assembly on cream phenolic boards with color-coded carbon composition resistors.
Key Features
- Resistance range: 15 ohms to 10 megohms
- Resistor wattage: 1W rated for all values
- Continuous operating voltage: 500V maximum
- Shorting-type rotary switches with make-before-break action - no open circuit during switching
- HI/LO range selector toggle for coarse range switching
- Two binding post terminals for direct circuit connection
- Passive device - no external power required
- Dual circular resistor wafer assembly on cream phenolic board; color-coded carbon composition resistors
- Approximate dimensions: 6" L x 3" W x 3" H
Applications
- Experimental determination of correct resistance values in circuit design and development
- Identifying unknown or unmarked resistor values by substitution
- Calibration verification for ohmmeters and multimeters
- Vacuum tube circuit work - plate, grid, cathode, and screen supply circuit testing
- Radio and television service bench work
- Simulating resistive sensors in automotive diagnostics
- Electronics education and lab demonstrations
- Makers and experimenters prototyping analog circuits without stocking every resistance value
Frequently Asked Questions
Does this unit require external power to operate?
No. The IN-37 is a fully passive device. It connects directly to the circuit under test via its two binding posts. No batteries or power supply needed.
What is the wattage and voltage limit I need to stay under?
Resistors are rated 1 watt. Continuous operating voltage must not exceed 500V. Exceeding either rating risks damaging the unit.
Are the resistance values accurate on a vintage unit like this?
The unit tested functional. However, carbon composition resistors used in vintage Heathkit equipment are known to drift in value over time. For critical or precision applications, verify individual switch positions against a known-accurate meter before relying on the indicated values.
What is the switch type and does it cause an open circuit between positions?
The IN-37 uses shorting-type (make-before-break) rotary switches. The circuit is never broken between adjacent positions during switching - the new contact is made before the old one releases.
Is a manual included?
Not included.
Carbon composition resistors, phenolic wafers, and shorting-type switches - this is bench hardware from an era when you built your own tools and trusted what your hands made. Plug it in, dial a value, and get back to the work.
