Playing with an oscillator circuit on 107 MC: results and schematic with a BD 139 (critical bias)

Please read the description/textbox first. In this video: playing with a circuit of an oscillator that works around 107 MC (MHz), made with a BD 139 NPN Si Transistor with a Hfe of (approx.) 150. It works best on 12 Volt-14 Volt.


It shows how critical the biasing of the HF (High Frequency) transistor is. Here a BD 139, medium power transistor for max. 3 Watt effective, is used. Here used in the 30-50 Milliwatt range.

There is only one small point somewhere on the wiper of that 22 K or 25 K potentiometer where the (read: this….= typical) circuit starts to oscillate. In some other circuits that biasing into oscillation is (somewhat or much more) less critical; anyway the video shows the (good) practice of how to get a transistor into oscillation and how to bias it in this type of circuit.

• By the way: there are broadband transistor oscillators, that are not so critical and can ”handle” all kinds of coils. The typical inductance that they can handle, making all kinds of coils into oscillation, could be in the 5 Micro Henry, to the small Milli Henry range, say 0.5 Milli Henry, on their input, getting all of them into oscillation. They can be: a FET (gate), a Radio Tube, (grid, often a triode), or a bipolar High Frequency (HF) transistors (on their base).

• Bipolar transistors in HF oscillator circuits (2 MC-300 MC) are often used in the grounded base mode (videos are on my YT channel, at least about the grounded base mode of a bipolar transistor and about the grid dipper). Search for more info on the www. e.g. for “dipper circuits” (grid dipper, transistor dipper, etc.). Or via the "looking glass" on my channel trailer, "Radiofun232". Type there keywords about the electronics that you are interested in, say audio, radio, shortwave, filters, etc.

• Germanium HF transistors in general are more easy to be brought into oscillation, due to their low barrier voltage (0.3 V) and their tendency to be unstable. Say the AF 239 or the AF 118. All very obsolete, but they work good in grid dipper circuits on HF and VHF and even in the UHF range (only the Germanium AF 239).

• Please don’t push up the energy of this (kind of) broadband radio oscillator too high. Be aware of the fact that radio communication with airplanes is (in general) AM modulated and goes in the 110 MC-130 MC frequency band. This is a disclaimer & you are warned.

• Of course the circuit strays out only in the (20-30) Milliwatt range, usable to be received in-between a distance of 10 meters or so.

My You Tube channel trailer is here: When you search, search always “NEWEST FIRST” to get the right overview. You can also search via the “looking glass” on my Channel trailer via keywords like ”audio”, “radio”, “amplifier”, “filter”, “Shortwave”, “transistor”, “FET”, “oscillator”, “generator”, “switch”, “schmitt trigger” etc; so the electronic subject you are interested in. My books about electronics & analog radio technology are available via the website of "LULU”, search for author “Ko Tilman” there.

I keep all my YT videos constant actual, so the original video’s with the most recent information are always on YouTube. Search there, and avoid my circuits that are republished, re-arranged, re-edited on other websites, giving not probable re-wiring, etc. Some persons try to find gold via my circuits. I take distance from all these fake claims. I can not help that these things happen. Upload 19 July 2022.
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