Old Federal Electronic Sirens

Mid-1960s Federal PA20 siren with 'alert' tone.

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This is a hobby web site, not a commercial web site.  I do not sell, trade, or repair sirens.  I designed this page to assist those who are looking for a period correct model of Federal Electronic siren for the restoration of an older emergency vehicle.   This site is also not affiliated with the Federal Signal Corporation in any way.

Federal lights and sirens were the most common brand found on North American emergency vehicles, and the company's history dates back to the early twentieth century.  Federal electronic sirens have been in production since the late 1950s, and like any other piece of technology they have undergone a process of evolution. 

This page is devoted to the standard full-size electronic siren, which is typically installed in fire engines, ambulances, and marked patrol cars.  Motorcycle and undercover sirens are not included here.  The historical timeline stops at the introduction of the PA300, a siren that was introduced in the early 1980s and is still in production today.

Bear in mind that this is just a rough guide to assist in restoration, and the collection of factual data is still a work in progress.  Photos and information on older electronic sirens are hard to come by, and if anyone would like to add something to this page, click here to contact me.
 

History of the electronic siren

One of the earliest known electronic siren designs used vacuum tube technology and was developed by William Fleming of San Leandro, California in the late 1940s.  Fleming's design was patented in 1951, and he had several objectives in mind with his rather novel invention.  First, he noted that the traditional electromechanical siren requires a lot of current to operate, as the electric motor must be powerful enough to spin the rotor (the rotating turbine or fan) and force air through the stator (the little square openings in the siren housing) to produce sound.   Fleming's device used only a fraction of the current, and he claimed that it would place less strain on a vehicle's electrical system.  Second, electromechanical sirens were manually operated, and therefore would work only when a button or foot switch is pressed and released by the operator.  Fleming's electronic siren allowed hands (or foot) free operation, as it was capable of producing a continuous wailing sound.  Third, the electronic siren requires an audio amplifier and a loudspeaker to function, and Fleming claimed that his device could double as a mobile PA system if a microphone was connected to it. 

The problem with this device was that the components of the time made it quite bulky, and other inventors developed subsequent devices that were smaller and would take up less space inside the cab of a vehicle.  When transistors came into wider use, more compact designs were possible, but with tubes or transistors there was always a problem of overheating when components were located too close together.  One solution was to separate the controls from the oscillator and audio amplifier circuits, somewhat like the control head/remote amplifier siren systems that are used today. The remote amplifier would have a grille or a heat sink to keep the transistors cool, which in turn would ensure more reliable operation. Wiring these two components together was not as simple as it is today, so it made for a rather awkward arrangement.

In the late 1950s, Gerald Smith attempted to address this problem by building a compact self-contained siren control/amplifier unit with power transistors attached to the outside of the chassis, where they would be kept cool in the open air.  Smith's siren was patented in 1962.  It was this design that would form the basis for many others, as it was small enough to attach under the dashboard of a vehicle.  As the 1960s progressed, several manufacturers were producing sirens that were based on Smith's design, including Federal, Trippe, General Electric, Dietz, Sireno, Motorola, and others.

If you are curious about some of the other brands of electronic sirens, click here to view some pictures of various 'vintage' sirens.

Technology

For about twenty years electronic siren circuitry remained basically the same.  The siren tones were generated in a grid of transistors, resistors, and capacitors known as a siren oscillator or timing oscillator/sweep oscillator circuit.  New sounds were added along the way:

Yelp: PA5 & PA10, early 1960s
Alert or 'steady' tone: PA15 & PA20, early to mid 1960s
Hi-Lo (European) tone: PA20A, late 1960s.

By the early 1980s other manufacuturers introduced new tones, including the 'air horn' sound, which sounds like a rather feeble attempt at imitating the growly Grover 'Stutter Tone' air horns used on some fire engines in the United States.  This sound resembles an electronic buzzer more than an air horn, and today this tone is available on most major brands of electronic sirens.   The PA300 was Federal's first full-size siren with the air horn tone, and this design marked the end of  traditional transistorized siren ocsillator circuits.  Integrated circuits (ICs) are used to produce the siren tones, and the PA300 uses separate IC chips for each of the sounds.

The use of ntegrated circuits and the application of digital electronics technology meant that it was possible to come up with a siren design that would more accurately reproduce the sound of an electromechanical siren.  This came a step closer to reality when Federal introduced the EQ2B, an electronic siren that uses digital signal processing to mimic the sound of Federal's famous Q series electromechanical sirens.  Only time will tell whether electromechanical sirens will be done away with entirely, as the Q is still quite popular among fire departments in the United States.

Applications

Electronic sirens didn't come into widespread use until the early 1970s.  In the 1960s they were somewhat of a novelty, and the sirens of that period were not without problems.  The Director and Interceptor models underwent several internal design changes right up until the beginning of the 1970s, which likely meant that the earlier models were not very reliable.   If you are restoring an older vehicle, just remember that the further back you go in time, the harder it will be to find a period correct siren.  It is fine to install an older siren in a newer vehicle, but not the other way around if you want historical accuracy.

For example, suppose you are restoring a 1970 Superior Cadillac ambulance and you can't find a 1960s Federal electronic siren.  Then your best bet would be to go with a mechanical siren, as the 'station wagon' or 'hearse' style ambulances from 1970 on back were more likely to be equipped with electromechanical sirens.

The 'Director' and the 'Interceptor'

Obviously the two most common models of older Federal electronic sirens were the Director and the Interceptor.  Some people believe that one model was better than the other for various reasons, but in actuality they were of the same basic design.  The major difference between the two sirens is that the Director is the 'economy' model and the Interceptor is the 'deluxe' model.  

Dating a Director or Interceptor

That being said, there were many different variations of Directors and Interceptors produced over the years.  The typical 'brown face' Directors and 'blue face' Interceptors emerged in 1962, and these models were in production for about 20 years.  On the surface, they basically look the same, and throughout this rather long production period the physical appearance of these sirens had changed very little, as shown in photo below.

Three styles of 'Interceptor' chassis covers.

Left:  PA20 with short solid  chassis cover,  early to mid-1960s.

Centre:  PA20A with long solid chassis cover, late 1960s.

Right: PA20A with perforated chassis cover, 1970s.

Chassis covers were always painted in a flat light grey finish.  Other colours such as black, white, cream, or beige would indicate a re-paint job by the previous owner.

If you intend to use either a Director or Interceptor for your restoration, you have to be very careful in choosing a period correct unit.   Looks aren't everything.  The big changes to these models occured internally, as you can see in the photo below.   All three sirens are Federal Interceptors, but from different production periods.  Three different circuit boards, three different siren sounds.  And believe me, I've tested each of these sirens and they sound very different from each other!    

 

Left: PA20, series E1C, mid-1960s.      Centre:  PA20A series 2D, late 1960s - early 1970s.      Right:  PA20A series 2E, early 1970s to early 1980s.

PA15 and PA20 versus PA15A and PA20A

The PA15 and PA20 have wail, yelp, and alert tones.  The alert tone is a steady tone that doesn't rise or fall.
The PA15A has wail and yelp tones only.
The PA20A has wail, yelp and hi-lo tones.  The hi-lo tone is an electronic simualtion of the high low horn that was used in European emergency vehicles.

PA15A and PA20A sounds:  low pitch vs. high pitch

This was what really got me obsessed with electronic sirens.  After listening to electronic sirens for so many years I've found that not all sirens sound alike.  I will pound my fists on the table and yell again and again, sound sound sound! The older sirens sound different than the newer sirens. The sound of the siren is the best indicator of period correctness.

The PA15A and PA20A sirens with serial numbers that have the letters  A, B, C, or D  have low-pitched wail and yelp tones. The 'wail'  tone rises slowly to the highest note, and the yelp is a 'wah-yu wah-yu wah-yu' kind of sound, almost like a human voice.  These sirens were in production from 1967 up until the beginning of the 1970s.  Furthermore, there were some emergency vehicles dating as late as 1972 that were fitted with early PA15A and PA20A models.

In  the early 1970s, the deep tones were clearly abandoned in favour of higher pitched sounds. PA15A and PA20A sirens with the letter 'E' in the serial number produce high-pitched wail and yelp tones just like the electronic sirens we hear nowadays.   The yelp tone make a 'wee-yow wee-yow wee-yow' sound, almost like a puppy dog barking rapidly.  Someone told me that one reason why Federal went to the high-pitched tones was because smaller speakers with short re-entry cones were introduced  in the late 1960s.  Federal's TS100 speaker, a compact speaker designed to fit in the classic Twin Sonic light bar, is smaller and shorter than the SA24, CP25, and CJ24 speakers that were in use throughout the 1960s and into the 1970s.   The high-pitched PA15A series 1E and PA20A series 2E were supposedly introduced in 1970, but I did not hear any of  these sirens until around 1973.

Federal TS series loudspeakers. 

The TS100 is rated at 100 watts and the TS 24 is 58 watts.  These speakers are designed to fit inside the centre grille compartment of  Federal's Twin Sonic light bar.   These speakers are quite small and have short re-entry cones, and small speakers tend to reproduce high frequency sounds better than lower frequency sounds.  This may be one reason why the PA15A and PA20A circuits were redesigned to produce high-pitched wail and yelp tones.  The PA15A series 1E and PA20A series 2E were introduced not long after the TS series speakers went into production.  

Nowadays, most siren speakers are of a compact design, and some are even shorter and flatter than the TS series.  And nearly all of the electronic sirens that are currently in production have high-pitched  wail and yelp tones.

Siren or synthesizer?

An electronic siren generates sound just like a keyboard synthesizer, only it plays just two notes.  On a synthesizer, the player can raise and lower a note with a pitch bending wheel, or on earlier keyboards the pitch can be raised or lowered between two notes in what was known as 'portamento' mode.   A switch was thrown, and the moment a low key and then a high key were pressed, the note would 'rise' to the higher pitch.   Notes could rise and fall gradually, rise suddenly and fall gradually, rise and fall suddenly, or rise gradually and fall suddenly, depending on how slowly or quickly the pitch bender or keys were manipulated.

This gradual or sudden rise or fall in musical notes is what makes various brands and models of sirens sound different from each other, and it all has to do with the design and the electronic components that are used the siren oscillator circuit.  For example, an early Federal PA300 has a wail tone that rises gradually and falls suddenly, while later models have a wail tone that rises suddenly and falls gradually. 

The earliest Federal electronic sirens were designed to simulate the sound of a mechanical siren.  Click on the link below and listen to the recording of the PA5, the earliest version of he 'Director' model.:

Sound samples:

pa5.mp3   PA5, c.1961-1962..  Sounds somewhat like the Q series mechanical sirens.

pa10.mp3   PA10, c.1961-1962..  Wail tone rises and falls like a mechanical siren but has a more rounded synthesizer tone like later electronic sirens.  This may be due to the type of speaker used in the demonstration..

As time went by the siren circuits were redesigned,  redesigned, and redesigned again so that they sounded more like synthesizers than real sirens.   While the first version of the Director (PA5) sounded close to an actual siren, the final version (PA15A series 1E) does not sound like a siren at all. 

The most common types of older Federal electronic sirens are those with the four 'classic' Federal electronic siren sounds listed below.  

Sound samples:

pa15pa20.mp3    PA15 and PA 20. Very deep sounding wail and yelp tones, c. 1962-1966.  They sound just like the siren sounds used on TV 'cop shows' in the early 1970s.

early15A20A.mp3    PA15A & PA20A series A-D.  Late 1960s wail and yelp tones, c. 1967-1970.  Deep, gradually rising and falling tones.