geccoo
Newbie
Hello! This is my first post, so sorry if it's a bit substandard.
I have just started getting into RF electronics, and I really wanted to try and build an amplifier for the FM band, since I have a small 250mW PLL FM transmitter.
I found a PCB layout on the internet, that looked to me, pretty simple and easy to put together. I gathered the parts and threw it all together, and I think it turned out OK.
I connected a 50 ohm dummy load, the PLL 250mW transmitter via a smaller gauge coaxial cable to the input & 12V regulated supply, current limited to 1.5A (if anything goes wrong) since the 2SC1971 is only rated for 2A, and it shouldn't draw more than 600mA when operating, with an input of 500mW from what I've read. And I'm only giving it 250mW (which in the datasheet says should give me around 4W of output which is enough for me).
The problem is that as soon as I turn the thing on, the power supply maxes out at 1.5A and the transistor get's pretty hot. I have checked for shorts multiple times and it's driving me crazy since there are none.
If I turn the voltage down from 12V to around 8V the current drops from 1.5A to around 600mA/500mA but it's still not outputting any RF, when the voltage is dropped even lower to around 5V it's not drawing any current at all. Is the drive to small or is there something wrong with the biasing? :???:
The two 220pF capacitors in the beginning are substituted for one 470pF and the 1.2nF for two 1nF, could this be the cause of the problem? And also, there's 50mW less of drive power. I asked one of my buddies who's a lot more into the RF section of things, and he told me it shouldn't cause any problems. Otherwise is the 2SC1971 fake? I ordered them from China a while ago, and to me they look like the Eleflow copies, which I've heard to work OK.
Here's the schematic:
I have just started getting into RF electronics, and I really wanted to try and build an amplifier for the FM band, since I have a small 250mW PLL FM transmitter.
I found a PCB layout on the internet, that looked to me, pretty simple and easy to put together. I gathered the parts and threw it all together, and I think it turned out OK.
I connected a 50 ohm dummy load, the PLL 250mW transmitter via a smaller gauge coaxial cable to the input & 12V regulated supply, current limited to 1.5A (if anything goes wrong) since the 2SC1971 is only rated for 2A, and it shouldn't draw more than 600mA when operating, with an input of 500mW from what I've read. And I'm only giving it 250mW (which in the datasheet says should give me around 4W of output which is enough for me).
The problem is that as soon as I turn the thing on, the power supply maxes out at 1.5A and the transistor get's pretty hot. I have checked for shorts multiple times and it's driving me crazy since there are none.
If I turn the voltage down from 12V to around 8V the current drops from 1.5A to around 600mA/500mA but it's still not outputting any RF, when the voltage is dropped even lower to around 5V it's not drawing any current at all. Is the drive to small or is there something wrong with the biasing? :???:
The two 220pF capacitors in the beginning are substituted for one 470pF and the 1.2nF for two 1nF, could this be the cause of the problem? And also, there's 50mW less of drive power. I asked one of my buddies who's a lot more into the RF section of things, and he told me it shouldn't cause any problems. Otherwise is the 2SC1971 fake? I ordered them from China a while ago, and to me they look like the Eleflow copies, which I've heard to work OK.
Here's the schematic:
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