Circuit of a 2 transistor Germanium (AC 187 NPN) audio pre amplifier.
Music by "the 127ers". They make very good music also to test amplifiers.
As far as I could see and hear the sound differs from the use of Silicon transistors (BC 547’s NPN) in exactly the same electronic setup (=a grounded emitter amplifier).
Also other types of (small signal) Germanium transistors can be used, as long as they are NPN types (at least in this schematic, perhaps I will publish a circuit with Germanium PNP transistors later) and their Hfe (current amplification) is between 30 and 70 or higher.
A little bit critical is the biasing. That means: set the Germanium transistors to their proper “working point”, where a sine wave is amplified completely pure, both the positive and the negative part of the sine. That is done with the 22 K potentiometers, aligning them to the exact point where a sine wave at the input appears purely amplified on the oscilloscope at the output.
Depends on: the Hfe (amplification factor) of the Germanium transistor and the supply voltage + the position of the 22 K potentiometer.
With this circuit and with using (a) bias potentiometer(s) you can also get low amplifying Germanium transistor into proper use. Say: Hfe 30 x Hfe 30 = 900. Could be enough.
Much more instruction about biasing of Germanium transistors via precise setting of the voltage divider on their base is in the video.
Correction: on 7.31 I say 500 KC (KHZ) but I mean 500 Hertz.
My You Tube channel trailer is here: [ Ссылка ]
There are (some) links to my video’s on YT available on my Channel Trailer in the “comments” section. Select, in the comments section, always “NEWEST FIRST” to get the right overview.
My books about electronics & analog radio technology are available via the website from “LULU”, search for author “Ko Tilman” there.
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Some of my books (not all) are available via Barnes and Noble and via Amazon.
But all my books (the complete bunch) are/is available on the website of LULU.
Regarding all my video’s: I constantly keep them actual, so the original video’s with the most recent information are always on YouTube. That is the source, and search there. When my video’s are reproduced or re-edited on other websites/channels you can not (!) be sure about the original content (=really working electronics with real properties for a purpose) and important adaptations to the circuits.
Be aware of that, I saw on the internet my circuits reproduced in a poor or not proper way.
I also found that people probably republish my circuits under phantasy names and/or with phantasy properties, attributing electronic properties to them that they were never made for, so phantasy properties. Sometimes they want to find gold with them. I take distance from all these fake claims; I cannot help that it happens, sorry. Upload 5 July 2020.
Video not made for children.
