Replacement for the RF amplifier / mixer IC CA3028A
Many ICs stated in older receiver building instructions contain fairly simple internal circuits. The replica of such ICs with individual components is very interesting. But it do not reach the same characteristics in all circuits or sometimes it does not work at all. However, this opens up new possibilities for circuits that work with it: It is now possible to make measurements within the "IC" and carry out modifications that are not feasible with the original ICs.
In addition, some older ICs are difficult to procure, e.g. the differential amplifier CA3028A. It is often found in old receiver circuits as mixers (e.g., Göttinger Baby II) or RF amplifiers. For this here an equivalent with common single components.