This circuit was found in a documentation of the 80s, having didactic purpose. For R1 values between 10k to 1M can be used. Transistors are general purpose types.
This simple AM transmitter for very small ranges uses in the original version of the 1970s, a...
The HA2620 integrated circuit used in this comparator is from the 80's, but the setting can be...
Figure 1 shows a circuit than can be used as time stage in timers, and other applications....