Identifying Zener Diode and Monolithic Amplifiers in Vintage Chinese Noise Source Circuit

hi, I need to identify the components in the circuit. Its noise source, old and from china. In left corner it must be zener diode, next to it monolithic amplifiers. If you have experience with these, please let me know.thx

Hi,
identification of Zener diode could be correct. Regarding the other device, its identification it's not an easy task, since the component markings have been intentionally erased.

thx for reply

I agree with tomas589 and Stefano that the part on the left is a zener diode, with the anode grounded and the cathode fed through a string of resistors (the black parts with numbers) from the + supply. The four-pin parts are monolithic amplifiers. For each amplifier, the top and bottom pins are grounded, the left pin is input AC-coupled through a capacitor (the brown part), and the right pin is output AC-coupled through a capacitor and DC-coupled to a string of resistors from the + supply. Mini-Circuits makes similar amplifiers.

identification of Zener diode could be correct. Regarding the other device, its identification it’s not an easy task, since the component markings have been intentionally erased.

thx for reply

I agree that we can't read the missing markings on the amplifiers. However, inspecting the connections to the amplifiers shows that various standard amplifier parts could work. In particular, the Mini-Circuits MAR-6SM+ amplifier would work on this board if we increased the values of some resistors. The datasheet states that the MAR-6SM+ is "Exact footprint substitute for Avago's MSA-0686", showing that we are dealing with multiple-sourced standard parts. The MAR-6SM+ uses Mini-circuits WW107 package, which is the same size and shape as the amplifiers on the board, and the MAR-6SM+ pinout agrees with the connections on the board. The MAR-6SM+ has 2000 MHz bandwidth, and the circuit label specifies 1500 MHz, so we are in the ballpark. From the label, the DC supply is +12V. From the MAR-6SM+ datasheet, the series resistance from +12V to the MAR-6SM+ output should be 536 ohms. From the photo of the PCB we see resistors from +12V to amplifier output. For first amplifier, resistors sum to (62+62+??=124+??) ohms. For second amplifier, resistors sum to (300+56+56=412) ohms. Thus, the resistors would have to be changed if we wanted to replace the amplifiers with MAR-6SM+ chips. The Zener diode is the source of the noise, and the two amplifiers increase the noise to the desired output level.