1950's "American Flyer Air Chime Whistle"

I am not sure if this is what you are looking for, hope it might help

Ray

The "Speaker" is not a conventional speaker. There is no magnet core, but a vibrator coil that picks up the frequency and produces the sound. The replacements you can find are simple magnet core speakers and work poorly.

The tubes are all the same inside and frequently to not work. You are correct, there is a simple point contact generator. Many times the tube must be gently cut open and the guts slipped out and the points cleaned.

Gandy

The ones pictured are the later versions of whistle generators. They all sounded like a buzzer.

The "tubes" are vibrators of the type used in car radios before 1958. They put an approximately 135 Hertz signal on the track.

The vibrators can often be renewed buy the use of 110 volts in series with a 100 watt incandescent light bulb. Don't do this if you are not intimately familiar with the power and dangers of electricity.

There is an earlier generator design with an actual vacuum tube in it and a pair of neon bulbs set up for dual relaxation oscillators. If you play with the capacitor values, you can get a more credible whistle sound, just before they get unstable. This system was expensive and the volume was lower than Gilbert wanted it to be.

Yes, Roy is correct. The early whistles were the Electronic Whistle, and came with a strange ceramic speaker. These are mostly found in the early Alco PA's. Gilbert did use an odd ball magnet based speaker in the GP-7 due to lack of room inside the shell. If your planning on using a magnet core speaker you may want to see if you can get the capacitor and resistor values from a GP-7 and use those for your experiment.

Gandy

Thank You all for the info and ideas. I'll see what I can do  ...

Would there be a simplified method for me to hook up a more ordinary speaker to try out my "tubes" ?  I don't expect to try to use it for an on-board speaker, which I don't have anyway.

The diagram above appears to show a resistor and condenser (capacitor) in series with the speaker, but I'm hearing that it's not an ordinary speaker. I'm fairly competent with electrical and electronic work.

The one shown in Rays schematic is a later "speaker" with the vibrator unit inside.