Datasheet BC547 Philips
http://www.datasheetcatalog.org/datasheet/philips/BC546_547_3.pdf
 
 

250mW audio amplifier
Here is a very simple three transistor audio amplifier circuit that can deliver 250mW to a 8Ohm speaker.
http://www.circuitstoday.com/250mw-audio-amplifier

Audio power LED
Dit is een schakeling die met een tweekleuren LED aangeeft hoeveel vermogen een versterker levert. De schakeling wordt aangesloten over de luidspreker-aansluitingen.
http://www.circuitsonline.net/schakelingen/156/audio/audio-power-led.html

Battery Equality Monitor
Almost all 24V power systems in trucks, 4WDs, RVs, boats, etc, employ two series-connected 12V lead-acid batteries. The charging system can only maintain the sum of the individual battery voltages. If one battery is failing, this circuit will light a LED.
http://circuits-projects.blogspot.com/2012/09/battery-equality-monitor.html

Digitale tester
Dit testertje kan het logisch niveau van digitale signalen aangeven op een 7-segments display. Het display geeft een H aan als het ingangssignaal hoog is. Wanneer het signaal laag is, geeft het display een L aan. Als de ingang open is dan geeft het display N aan.
http://www.circuitsonline.net/schakelingen/25/meten-en-testen/digitale-tester.html

Simple receiver For 40 and 20 M with an unusual tuning control by PA2OHH
Geert Paulides PA7ZEE had a nice idea, a homebrew competition of a shortwave receiver!!!
It was a nice opportunity for me to do some experiments with a direct conversion receiver with the RA3AAE mixer.
http://www.qsl.net/pa2ohh/07swrx1.htm

FKM QRP 5 Tranceiver door PA3FKM
Dit ontwerp heb ik gemaakt naar aanleiding van veel opmerkingen van Robert over diverse andere ontwerpen voor eenvoudige kortegolf tranceivers met klein vermogen.
http://pascal.nedlinux.nl/zelfbouw/FKM-QRP-5.html

FM Radio Receiver
This simple fm radio receiver circuit consists of a regenerative rf stage, TR1, followed by a two of three-stage audio amplifier, TR2 to TR4.
http://www.electroschematics.com/5923/fm-radio-receiver/
 

General Coverage Receiver by ON6MU
This is a compact three transistor regenerative general coverage receiver with fixed feedback. It's based on the principle of the ZN414 only much higher coverage. The sensitivity and selectivity is relative good (especially on the LF and MW bands) as can be expected with this "simple" design.
http://users.belgacom.net/hamradio/schemas/generalcoveragereceiver.htm

A good regenerative receiver with simple fine tuning by PA2OHH
When you add an LF stage and a fine tuning to the simple receiver with only one fet, you will have a much better regenerative receiver.
http://www.qsl.net/pa2ohh/08regrx.htm

Knipperlicht
Dit is een ontwerp van een eenvoudig enkel knipperlicht. Deze kleine schakeling is binnen een halfuur op te bouwen. De schakeling werkt van 4,5 tot 12 V. Natuurlijk is het ook mogelijk om andere zaken dan een LED aan te sturen.
http://www.circuitsonline.net/schakelingen/12/lichteffecten/knipperlicht.html

LED lichtorgel
Dit is een leuke schakeling die bijvoorbeeld gebruikt kan worden op feestjes. De 4 LED's knipperen op de maat van de muziek. Het lichtorgel reageert met behulp van een microfoon op geluid.
http://www.circuitsonline.net/schakelingen/63/lichteffecten/led-lichtorgel.html

Lichtketen
Dit is een eenvoudig knipperlicht dat een keten van LED's laat knipperen.
http://www.circuitsonline.net/schakelingen/84/lichteffecten/lichtketen.html
 

Light Relay Switch By BC547 & BC337
This circuit is simple form but can be useful various such as The alarm circuit, an more electronic control circuits such as ON-OFF electrical equipment, the flash light control circuit or etc. following with do you want.
http://www.eleccircuit.com/light-relay-switch-by-bc547-bc337/

Long Range FM Transmitter
The VHF-FM transmitter described has a power output of between around a half and 2 watts, depending on the power source, which may be anywhere between 6 volts and 30 volts d.c.
http://www.circuitstoday.com/long-range-fm-transmitter-1

Mini Alarm
This circuit, enclosed in a small plastic box, can be placed into a bag or handbag. A small magnet is placed close to the reed switch and connected to the hand or the clothes of the person carrying the bag by means of a tiny cord.
http://www.hobby-circuits.com/circuits/alarms-and-security/alarm/656/mini-alarm/

Portable Regenerative Receiver With Very Low Supply Current by PA2OHH
It is a modern portable version of the historical regenerative receiver, with transistors and a short telescopic antenna plus RF preamplifier. And it is a real QRP receiver, supply is only 2 mA at 6 volt.
http://www.qsl.net/pa2ohh/02reg.htm

Small Portable Regenerative Receiver by PA2OHH
The Big portable regenerative receiver is quite successful. The electronic circuit would be very suitable for a small portable receiver if there were not so many controls and switches.
http://www.qsl.net/pa2ohh/03rega.htm

Preá Regenerative Receiver by PY2OHH
Tropicalized version of the famous "Desert Ratt", regenerative receiver for SWLs, hobbists, listeners and radio hams. It uses 3 NPN garden type transistors and a LM386 as the audio amplifier. This receiver can be regarded as a QRP (low power) because the regenerative stage uses some microwatts in order to work.
http://py2ohh.w2c.com.br/trx/prea/prea.htm

Regenerative FM Broadcast Receiver
I must admit, at first I was sceptical looking at the circuit diagram, a single 1.5 V cell supply? But after a quick check of the audio stage bias with my calculator I saw that Mr Hall had designed it well, so I dug out the solderless breadboard and made up the audio strip. It "blurt" tested OK, and was surprisingly quiet and well-behaved (I used BC548B devices).
http://www.vk2zay.net/article/89

Simple Police Siren "US-Style"
The circuit described here can create three different ‘US-style’ siren sounds: police, ambulance and fire engine.
http://circuits-projects.blogspot.com/2011/04/simple-us-style-siren.html

Simple pre-amplifier with transistors BC547
The preamplifier circuit is a circuit that extends the signal from the source sound to signal the strength to go into a power amplifier circuit to trigger the required sector preamplifier is also due to signal from the source voice.
http://www.eleccircuit.com/simple-preamplifier-circuits-by-transistors/

Your first transmitter by PA3HCM
With just a few components, you can make your own morse code transmitter. The output is only a few miliwatts, but this is enough to receive on any radio in your home.
http://www.pa3hcm.nl/?m=200208