Federal’s ‘Director’ and ‘Interceptor’ Electronic Sirens
By: Leslie Erlich
So you found a 1970 Superior/Cadillac 54′ high headroom ambulance that is rusting away and you want to restore it to the way it was when it was new. The beacon and siren are long gone but you have a idea of what type of warning equipment it had when it was first put into service. Beacons are fairly easy to find – either a Federal 17 series or 184 series will do. But what about the siren? Should you go mechanical or electronic? According to the 1970 Superior catalogue, there were three mechanical siren options: A Federal Q, a Federal C6, or a B&M Super Chief. As far as electronic sirens go, only the siren speakers are illustrated in the catalogue: a Federal CP25, CJ24, SA24, and CJ184 speaker/light. But if the speakers were Federal, chances are the siren would have been a Federal Director or Interceptor.
If you choose to go with an electronic siren, the Director and Interceptor models are by far the most recognizable among the old Federal electronics, particularly the ‘brown face’ Director and the ‘blue face’ Interceptor. The brown face and blue face versions were in production for about twenty years, and on the surface they look pretty much the same regardless of when they were made. To the uneducated observer, a siren is a siren is a siren. But I will argue that surface appearance alone is not a valid indicator of period correctness. The Director and Interceptor sirens underwent several design changes throughout the course of production, and in my research I have found that the sound of the siren is the best indicator of period correctness.
PA5 and PA10
The very first Director and Interceptor sirens were the PA5 and PA10, and they only vaguely resembled their brown and blue faced cousins. The Director was intended to be the ‘economy’ model while the Interceptor would be the ‘deluxe’ model. The most significant features about both sirens are that the Director has a wired-in microphone and screw terminals for power/speaker/radio connection, while the Interceptor has an optional detachable microphone and multi-pin plug connectors for the radio, speakers, and power supply. The PA5 (Director) and PA10 (Interceptor) had black control panels and grey plastic knobs, and they were both capable of producing the standard wail and yelp tones that are still featured on electronic sirens today. But the one thing that really set the PA5 and PA10 apart from later Federal electronic sirens is that these models were designed to simulate the sound of a mechanical siren. I’ve heard a PA5, and the ‘wail’ tone sounds much like a Q2b mechanical siren. The PA5 and PA10 were in production from about 1960 to 1962, and either one in working condition would be a rare find.
PA5 sound sample: pa5
PA15 and PA20
The brown face / blue face era began with the PA15 and PA20 around 1962. What sets these sirens apart from later versions of the Director and Interceptor is that both models have wail, yelp, and ‘alert’ tones. The ‘alert’ tone is just a steady tone that plays at constant pitch – it doesn’t rise or fall. Federal abandoned the simulated mechanical tone in favor of a more rounded synthesizer-like tone when the PA15 and PA20 were introduced. The sound of these sirens is much deeper and lower-pitched than what we are accustomed to hearing nowadays. I’ve never heard a PA15 or PA20 in use on a ‘real life’ emergency vehicle, but I have heard the PA15/PA20 sounds on many TV shows and movies that were produced from the late 1960s right on up to the early 1980s. For example, the siren sounds that were dubbed in for Squad 51 of Emergency and the patrol car on Adam-12 were a recording of a PA15 or PA20 running in ‘manual’ mode. Or the dual siren tones of the police cars on Hawaii Five-O were overdubs of PA15 / PA20 wails and yelps. Over the course of production the PA15 and PA20 underwent several minor internal design changes, but the circuit board layout remained roughly the same until the end of production. Letters at the end of the serial numbers indicated revisions to the circuitry, such a F1, E1, F1A, E1A, F1B, E1B, etc. PA15 serial numbers began with ‘F’ and PA20 serial numbers began with ‘E’. Production of the PA15 and PA20 ended in 1966.
PA15 / PA20 sound sample: pa15pa20
Early PA15A and PA20A
The PA15 and PA20 were replaced by the PA15A and PA20A in 1967. The PA15A has wail and yelp tones only while the PA20A has wail, yelp, and hi-lo tones. The hi-lo tone is an electronic simulation of the hi-lo horn sirens that were used on European ambulances. With the change in the control panel layout came a complete change in the design of the siren oscillator circuits. The early PA15A and PA20A models also had deep low-pitched tones, but the wail and yelp tones rose and fell a little differently than those of the PA15 and PA20. The wail tone rose more slowly, and the yelp had a distinctive throaty ‘wah-yu wah-yu wah-yu’ sound, almost like a human voice. PA15A serial numbers began with the number ‘1’, while the PA20A serial numbers began with the number ‘2’. The first number was followed by a letter – A, B, C, or D, and the letter indicated that there were changes to the circuitry. I’ve never seen an A series unit, so I’m assuming that it was either a prototype or demonstrator that never made it to full scale production. There are service manuals for the B, C, and D series however. The early PA15A and PA20A sirens were in production from 1967 to about 1970, although there seems to be a lot more 1D and 2D series units around than the earlier versions.
Early PA15 / PA20A sound sample: early15a20a
PA15A series 1E and PA20A series 2E
The Director and Interceptor siren oscillator circuits would undergo one last major change in the early 1970s. These units have the letter ‘E’ in their serial numbers. The circuit boards in the E series units are completely different from the earlier PA15A and PA20A units. The new models, PA15A series 1E and PA20A series 2E, would have high-pitched wail and yelp tones much like the electronic sirens we hear nowadays. Sometimes I have to listen closely to tell the difference between a Federal PA15A 1E or PA20A 2E and a Carson/SVP SA450! One possible reason for going to the higher pitched sounds was that more compact speakers were coming into use, and smaller speakers reproduce higher frequency sounds better than low frequency sounds. Federal’s TS100 speaker, the same speaker that is used in the TwinSonic light bar, is one such example. I first heard the high-pitched E series PA15A/PA20A sounds around 1973, although someone told me that the circuit was introduced in 1970. In any case, the PA15A series 1E and PA20A series 2E were in production throughout most of the 1970s and ended in the early 1980s. The 1E and 2E use 2N2925 transistors in the siren oscillator circuit, and the 2N2925 circuit was also used in the PA150, PA200, and PA1000 sirens. Besides the high-pitched wails and yelps, the other thing that makes the 2N2925 circuit unique is that goofy ‘in-between tones’ can be heard simply by turning the selector knob between wail and yelp or yelp and hi-lo. The E series are by far the most common version of the Director and Interceptor, but remember that they are 1970s models and were in production when many ambulance companies were switching to van-based units.
PA15A 1E / PA20A 2E sound sample: highpitch
In terms of outward appearance, the chassis cover is the most distinguishable feature when comparing the PA15 / PA20, early PA15A / PA20A, and PA15A 1E / PA20A 2E. The PA15 and PA20 have a short chassis cover, the early PA15A and PA20A have a long chassis cover with small ‘grille’ at the back, and the PA15A 1E and PA20A 2E typically have rows of holes on the back half of the chassis cover for ventilation. The latter two chassis covers are interchangeable, so a cover is not a reliable indicator of period correctness. I have a PA20A 2D with a 2E chassis cover, and on the surface it does look like a 1970s PA20A.
The circuit board is the most important part of the siren. This is where the wails and yelps com from, and the sounds of the sirens changed along with the circuitry. I have the three basic variations of the blue face Interceptor siren: a PA20, an early PA20A, and a PA20A series 2E. The circuit boards of all three sirens are entirely different, and they sound different too! The PA20 circuit board is brown, the early PA20A circuit board is a cream colour with a set of wires running over top, and the PA20A 2E board has all wires running underneath.
The serial number is stamped into a metal plate on the bottom of the PA15 and PA20, while the PA15A and PA20A have a silver-grey label on the bottom. There are at least nine different versions of the PA15 and PA20 and five different versions of the PA15A and PA20A. So for example if you have a PA20A with the serial number E1C, then you need to get a PA20 series E1C owner’s manual with the component location and schematic diagrams. Or if you have a PA15A series 1B, you need a PA15A 1B manual. A 1E manual won’t help because the board layout and components of a 1E are entirely different compared to the 1B.
So, returning to that 1970 Superior 54” high-top ambulance restoration – which siren to install? Either a PA15A series 1D or a PA20A series 2D. A 1B or 1C or a 2B or 2C would also be period correct. All of these variations have the deep low-pitched slow rising wail and yelp tones. Even a PA15 or PA20 would work, although they are much older sirens. And if you can’t find any of the above, a mechanical siren will do.
Leslie Ehrlich is a self proclaimed ‘armchair pro-car ambulance enthusiast and a siren fanatic’. We would like to thank him for sharing his extensive knowledge of the history of electronic sirens and warning equipment.