Unitrol 800 siren transistor question

Discussion in 'All About Sirens & Audible Equipment' started by Mike58, Jul 31, 2017.

  1. Mike58

    Mike58 New Member

    Hello everyone. I'm hoping for some help. I have an old Unitrol 800 series siren that has 2 blown SP3099 power output transistors. They are a TO-3 style matched pair located on the bottom of the unit. Does anyone know of equivalent replacements for these transistors? I can't seem to find them listed on data sheets anywhere. There is a third transistor, a 2N3055 NPN that checks out ok with a dvm in diode mode. The two SP3099's (PNP i'm guessing) are open circuit so i'm assuming they're blown and hoping equivalent replacements are available. The siren powers up ok and I can hear it faintly from a small piezo located on the internal circuit board. I just have no amplification. Also, does anyone have a manual in pdf for this unit? A wiring diagram and schematic would sure be helpful providing I can replace the two bad transistors. Any help and ideas are greatly appreciated. Thanks in advance.

  2. MtnMan

    MtnMan Senior Member

    Hi, Mike. Here's a schematic for the early Unitrol 80 sirens, using the same oddball SP3099 transistors, and a service bulletin that suggests several 2N series replacements. Good luck!

    Attached Files: Download all post attachments

  3. Mike58

    Mike58 New Member

    Hello MtnMan,
    Thank you for the info. I'm curious to see if i can revive this old unit. A matched pair of transistors will probably be a challenge to find but i'll look around. Thanks again.
  4. Mike58

    Mike58 New Member

    Unitrol 800 project update. So far so good. I was able to get the siren working today by replacing the dead SP3099 output transistors with Mospec 2N5683 PNP transistors. Powered up the unit and had full siren audio output. Tried the PA function but only heard clicking noises in the speaker when pressing the PTT switch on the federal signal mic i was using to test. Any ideas why no mic audio even though the volume control is at full right? Is a federal signal mic incompatible with this unit? Also how would i hook up a momentary switch so i can use the manual siren function? I know it involves the horn ring connections on the back of the unit but i don't have an installation manual to explain the wiring. Any more help would greatly be appreciated. Thank you so much.

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