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.

Like the CA3028A, the LM703 contains a differential amplifier, but it is slightly different. It was often used in receiver technology as an RF amplifier. In addition, it could be found in some commercially manufactured hi-fi radio receivers of the 1970s in the 10.7MHz IF stages of the VHF section. Here is the circuit of the recreated LM703.

In order to achieve a higher cut-off frequency, RF transistors with a higher transit frequency can be used. However, it is also important that the structure is as compact as possible and with short lines. The component side of the board should have a conductive ground surface.

The Siemens circuit SO42P is a symmetrical mixer that works on the principle of the so-called Gilbert Cell. It can also be operated as a self-oscillating mixer with or without crystal control. Furthermore, the use as a balance modulator in SSB transmitters or as a phase comparator in PLL circuits is possible. Here the replacement circuit is shown.

When replicating of RF ICs, the smallest possible cable lengths should be adhered to. Only in this way do the circuits come close to the integrated implementations in their properties. It is important to use low-induction resistors. Optionally, the characteristics of the circuits can be improved with different types as the specified transistors, if which have a higher transit respectively cutoff frequency.

This is the schematic of a discrete, i.e. built from single components operational amplifier.

The circuit can be used to build the basic usual OPV circuits, such as inverting amplifier, non-inverting amplifier, voltage followers, comparator, integrator, differentiator, etc.

The circuit shown here could be used instead of the PL81 in its standard configuration according to the data sheet as a replacement in old TV receivers or video monitors.

However, this was not a full replacement of the PL81. The circuit worked just in such standard applications and not in all possible with this tube circuits. The 56 ohm resistor useless converted heating power into heat so that the heater line of the TV receiver was not interrupted. Thus, the circuit, connected to a Noval plug, could be plugged into the tube socket for the PL81. Of course, the BF459 needs a heat sink.