On the boards of old TVs you can see TV tuners on the kinescope. These tuners use double-gate FETs and what’s called a MOSMIC (a dual-gate transistor with bias resistors inside) near the antenna jack. I am interested in double gate transistors and I will talk about them in this article
I got two tuners with double-gate MOSFETs. The first tuner is CK-B-568E. This tuner has a BF909R transistor. The inscription “M29” is on the body.This transistor is low-noise and can operate at a frequency of 1 GHz. Using such a transistor, you can assemble a generator or an amplifier for a radio receiver
Another tuner of the QAU0383 brand has a two-gate transistor with the inscription “BS” on the body; its full name could not be found.
How to test a two-gate transistor with a multimeter? The transistor has four terminals: drain, source and two gates. The widest pin is usually the source. The drain of the transistor is located nearby. On the other side of the transistor there are two gate terminals. Connect an ohmmeter to the source-drain circuit. The ohmmeter will show infinite channel resistance.
Bring your hand to the gates of the transistor but without touching them. The resistance of the drain-source channel will begin to decrease down to tens of ohms. Various electromagnetic radiation is induced on our body and there is also static. They affect the gates of the transistor and, accordingly, the resistance of the drain-source channel.
