Erector Set P48 gearbox and A49 electric motor

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https://mediastorr.com/a49

A-49 vs P-49 — what people really mean when they talk about the “P-49 gearbox”

A-49 is the famous A.C. Gilbert mains-powered Electric Engine used to drive Erector Set models.
P-49 is an 18-tooth gear that appears in many Erector drivetrains and very commonly inside or alongside A-49 gearbox setups.

When people say “P-49 gearbox,” they are usually not referring to a separate factory gearbox called P-49. They are almost always talking about the A-49 gearbox (or a custom gearbox build) that uses the P-49 18-tooth gear as one of its key gears.

Below are the well-supported facts, stats, and history.

A-49 Electric Engine — facts and stats

Electrical ratings seen on original motors and documentation include:
110–120 volts AC
60 cycles (60 Hz only)
Typically labeled 20 watts, with some documents listing 25 watts input

The small wattage difference comes from different printings, years, and “input vs rated” wording. What matters is that all A-49 motors are mains AC, 60 Hz, and in the roughly 20–25 watt class.

The A-49 gearbox — what it does

Forward / Neutral / Reverse
Many A-49 motors were paired with a gearbox that includes a Forward / Neutral / Reverse selector operated by a shift lever. This feature is well documented in original Erector materials and is commonly highlighted in collector descriptions.

Multiple speeds through gear ratios
The gearbox allows different gear combinations so builders can trade speed for torque. This is classic Erector behavior: fast rotation for fans or slow, high-control motion for hoists and cable winders.

What “P-49 gearbox” usually means

The P-49 is specifically an 18-tooth gear, usually brass, mounted with a set-screw hub.

So a “P-49 gearbox” is not a named gearbox model. It’s shorthand for a gearbox arrangement (often the A-49 gearbox itself) that uses the P-49 18-tooth gear as a driver or driven gear.

Documented use case
Erector manuals from the late 1920s describe cable-winding gearboxes where the small P-49 gear drives a larger gear to achieve high speed rather than high power. That explains why the P-49 shows up so often in gearbox discussions — it’s one of the standard small gears in the system.

History and evolution notes

Changes over time that collectors often notice:
Late 1930s to late 1940s: thin steel safety guards added over the gearbox top
Late 1940s: changes in motor mounting feet (round holes vs earlier slots)
Some years offered A-49 motors without the same gearbox configuration

A-49 is consistently listed in A.C. Gilbert reference material as one of the official electric motors supplied with Erector sets, distinct from mechanical or spring-driven motors.

Collector reality — what wears out

Common issues:
Hardened grease and dirty gears causing sluggish or noisy operation
Worn bushings or shaft play leading to poor gear meshing
Old power cords and plugs, which are a real safety concern since this is a 110–120V AC motor

What collectors value:
A working A-49 with intact gearbox
Shift lever present and functional
Safe, intact cord and plug

Quick ID checklist

You likely have an A-49 setup if:
The motor label says A-49 and lists 110–120V AC, 60 cycles, around 20W
The gearbox has a shift lever with Forward / Neutral / Reverse
You have an 18-tooth brass gear marked P-49 with a set-screw hub