wierd ring type thing... or Armstrong Green Ringer

[R.G. Keen]

>This is called an "Armstrong Green Ringer" by the inventor.  I can't
>remember who it was, but someone wrote that it looked like a fullwave
>rectifier, that is, assuming the "mystery part" is an NPN transistor
>operating like two common anode diodes.  After much farting around
>with it due to lack of exact components, I managed to make it work.
>Or rather I made *something* work.  I used a 15 volt supply instead of
>9 volts and I used 2N3904 and 2N3906 instead of the trannies called
>out, so I had to change most of the resistor values.
The schematic was taken from a tracing of the original effect. Ohmmeter
tests showed the part was indeed an NPN transistor used as diodes.

>However, using the EB junctions of two 2N3904 trannies or two common
>cathode 1N914 diodes worked equally well as a fullwave rectifier,
>verified by oscope.  When presented with a sine wave, the output
>frequency is doubled and some extra harmonics are audibly obvious.
Later versions of the same effect used discrete diodes.