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PM-8911 Beacon - Gyrating Warning Lights





'Prime' Beacons ----------- 'Federal Signal' Beacons

'15360 Gyralite' Beacon ----- Dietz 211 Beacon


Railroad that chose to divest themselves of the Oscitrol Lights used beacons as their warning lights.

The following beacons (Prime and Federal Signal Commander) use the 88PAR/FL sealed beam bulbs (PAR-36 75V 88W). These bulbs are classified as floodlights and are listed in the Prime specifications as 1550 candlepower.

An estimate of the beamwidth (50% cbcp) of these bulbs was made with a light meter (GE has no data on the beamwidth of these bulbs and it appears they are the only manufacturer). I found that these bulbs produced a compressed elliptical pattern having a beamwidth of 16 x 54. This bulb is used in 2 orientations. In the Prime beacons, the bulbs are installed with the 2 screw terminals in line horizontally. This will assure a horizontal coverage of 54 between the bulbs. In the Commander 372 beacon, the bulbs are installed with the 2 screw terminals in line vertically. This assures that there is a short ON interval (16) for maximum flash effect.

88PAR/FL filament support structure
200PAR filament support structure

The 88PAR/FL - 75 volt filament support structure for these bulbs utilized springs to absorb the shock of the fragile, higher voltage filament. The 200PAR - 30 volt locomotive bulb filament support did not need this feature. The fragility of the 75 volt filament is described below and on the Electrical Aspects page.


'Prime' Beacons

There were 3 popular solid-state beacon designs containing no rotating mechanism made by the Prime Manufacturing Corp. (7730 South 6th St./Oak Creek, WI 53154)

The domes on these units are made by Acutek, Inc. (777 Action Ave./Odessa, MO 64076).

The trademark for Acutek's products is "STRATOLITE". The covering used is documented by Acutek as being a No. 80 Dome (the trademark "STRATOLITE 80" is embossed in the top center of the cover).
This dome is made in amber, red, clear, blue, and green.

The original light unit was called a Prime 8901 Light. It used analog circuitry. The four bulbs were turned on and off using SCRs. The flashing rate in the circuit was controlled by a unijunction transistor. Since the flashing circuitry of the bulbs was in series, a single lamp burnout would tend to make the unit non-functional (see schematic).

This version was replaced with the PM-8911 model which had a lower base height and all digital circuitry (see schematic). A burnout of one bulb in this circuit would maintain flashing of the other bulbs.

The 8901 unit had a 5" base height whereas that of the 8911 was 3-5/16". The 8911 model was promoted as having the advantage of tolerating low clearances. The No. 80 Dome was used on both these models. Chicago's Metra used both amber and red domes. The latest model currently marketed by Prime is the 8913 series (produced in the mid 1990s). The 8901 and 8911 have been discontinued. The PM-8913 model is identical to the PM-8911 externally. There was a change in the male-female connector in the unit from 7 pins to 9 pins. The 7 pin connector was replaced to due it being expensive, hard to obtain, or both. A new circuit board was made up to accommodate this new 9 pin connector. These were the only changes stated by Prime. All components remained identical with that of the PM-8911. This led to the new model number - PM-8913.

The PM-8913 is marketed in the following forms (based on the power cord):
PM-8913-3 - has an 8 ft. cord
PM-8913-5 - has a 16 ft cord
There was a PM-8913-6 with no cord...but this supposedly is discontinued.


Most locomotives are equipped with two Prime beacon lights. The first, which always has an amber lens (dome) was applied to locomotives in order to comply with operating rules of the Chicago & NorthWestern (now Union Pacific) Railroad.

The second, which is generally red, but can be amber, acts as an alarm when the locomotive is on wayside standby power. The light is activated when the standby system trips or if the temperature of the locomotive drops below a pre-set value.

Richard L. Soukup
Meta -Chief Mechanical Officer


Temperature warning:

I suspect the low temperature is when the cooling water for the engine gets near freezing. Since the engines do not have antifreeeze, if the water freezes, it can ruin the engine. Most railroads have "Cold Weather Shutdown" procedures which either require the engine to remain running or the cooling water drained. Since Metra is in Chicago, I am sure they face some cold temperatures!

Bill Kaufman


There are 2 operating modes for Metra. One mode is for Metra locomotives running on UP trackage and another for non-UP trackage. The following Engineers explain the usage and function of the beacons (Amber and Red) as well as the single strobe units (see Strobes page) used on the non-UP Metra locomotives.

The amber beacon can be turned on and off by the engineer, but rules (UP) require them lit on both ends of the train at all times. The GCOR (General Code of Operating Rules) that most RR's use required the beacon, if equipped, to be illuminated on the lead unit of an engine consist.

There is a "Layover Alarm Test" switch to check the operation of the red beacon. It will only work if the HEP is operating or some such combination. Occasionally I have seen trains pass with the light illuminated. Usually we call them and tell them to kill that test switch.

I can only speak for the units assigned to the UP. Even though they are Metra locomotives, we have different rules. The CNW originally required amber beacons on both ends of commuter trains. They called them "Anti-Collision Lights", and used them because the red class lights on the old cab cars and F7's weren't really bright. When Metra came in, the rules carried over

I know the other Metra lines don't use the amber warning beacon, in fact many of the lower 100 series F40PH's don't have them. They instead have a yellow strobe mounted on the left side (fireman's side) of the cab roof.

Joel G. Kirchner


The amber beacon is connected only to a manual switch on Metra F40PH-2's. In former times on freight units, it was wired into the generator field circuitry, but I haven't seen too many units so equipped in recent times. The red beacon, however, is so wired into layover circuitry and will come on in a power failure. However, it has to be turned on via a switch in the electrical compartment next to the battery knife switch. The switch is one of a group of four and is labeled "Layover Alarm". It gets used mostly in cold weather due to the fact that if the locomotives aren't kept heated, they'll freeze up as they don't have antifreeze in their radiators. Unlike freight engines, we don't leave them running. The source of my information is the on-duty MIC at Waukegan.

Douglas Smith


Other users of this "bubble light" included SP, BN, Frisco, and the Santa Fe.

The advantages listed for the Prime unit were that it was all solid state, with no moving parts. Also, the sealed beam lamps were mounted in rubber boots for shock absorption. Rubber was also incorporated in the mounting of the base plate to the top of the locomotive.

On contacting Prime Manufacturing Corp., I was told that no information on the PM-8911 was available. The representative of the company said the light unit was out of production and that no information on a patent was available. The schematic, as well as the specification sheets were furnished from secondary sources.

In researching this unit, it appears that there may have never been a patent on it. The following patents seem to reflect, somewhat, the operation or design of this light as it was marketed:

US Pat. 5,694,112 "Solid State Rotary Beacon" filed on Dec. 12, 1994/granted on Dec. 2, 1997, was assigned to Grote Industries, Inc. in Madison, IN.

US Pat. 4,621,253 "Warning Light" filed March 7, 1983/granted Nov. 4, 1986, was assigned to Rotalight Limited in UK. This patent shows a circular arrangement of bulbs which flash in sequence to produce a pattern where alternate bulbs flash on and off in sequence. The unit is shown to be mounted with the circular bulb arrangement in a vertical plane. The circuit employs a timer IC, a counter IC, buffer transistors from outputs of counter IC, power transistors with input from buffer transistors and output to 2 alternate bulbs in the bulb circle. The PM-8911 uses a 4060 IC as a timer as well as a counter. The output of this counter is the input to the 4017 IC decade counter. Each output of the 4017 IC goes to a MOSFET. The buffer transistors are not needed, since the high impedance of the field effect transistors turn on with the direct output of the 4017 IC.


'Federal Signal' Beacons

The "Commander" series was one line of rotating beacons produced by Federal Signal Corp.
The patent covering these lights is US Pat. 3,271,735.

The Commander series had both an industrial model (no. 371) and a locomotive model (no. 372). These two lights looked alike. The base had vertical fins on it to dissipate heat generated by the bulbs. Both units used 2 sealed beam bulbs which were mounted back to back. The dome on the 372 was consistently amber. The Commander 372 was powered directly by the 72/74 volt locomotive accessory supply voltage.

There were revisions to this model as denoted by "A2", for example. The original 372 beacons had no voltage dropping resistors for the bulbs. The resistors were not a necessity since the bulbs were rated at 75 volts. The resistors were incorporated into the power to each bulb in order to prolong the bulb life. There was no appreciable loss of brightness in doing so.
There were 2 "straight through" capacitors that were put into the motor supply circuit, one in each of the 2 supply leads. These had a metal case which was secured to the light base, thereby grounding the cases of each. This suppressed rf interference from the motor's brushes.

Another revision to the units was the use of shock mounts to ease the vibration and shock to the filaments of the bulbs.

This bulb was a problem for filament damage due ot shock. The constant banging into cars in yard service was a challenge to the bulbs. GE made 4 revisions of this bulb to try to solve this problem. Since the bulbs were rated at 75 volts, their filament cross section diameter was small. There were discussions of going to a lower voltage bulb that would have a stronger (increased diameter) filament. Federal Signal incorporated shock mount design into the 372 units to cushion the filaments. During these countermeasures taken by GE and Federal Signal, apparently the railroads did not want to continue to use this beacon so it was removed and lost popularity.


Other Beacons:

The 15360 Gyralite was a popular beacon. It is discussed on the Gyralites page and on the Strobes page. This beacon was seen on lines such as the Soo and Milwaukee. The Soo used the base of this beacon as a mounting platform for the 6551 Safety Products Strobe.

Another beacon not usually seen on locomotives:
Dietz 211 Beacon