BF245, a JFET transistor produced for many decades by several companies, has joined the list of discontinued components. However an equivalent replacement exists in an SMT package and its name is BF545.
BF245 in a TO-92 package has been one of the first transistors, which were mass-used. That’s why it’s no wonder, that the BF 245 is nowadays familiar to every experienced technician. As a transistor with a very high input resistance (tens of MOhm) and a relativlely low noise, it’s gained a global popularity and served to many beginning technicians at an assembly of their first radio-receivers. There are many other FET transistors on the market nowadays, thus the usage of BF245 is substantially smaller. Moreover, a majority of electronics is produced with SMT components, what probably was one of more reasons why all main producers have discontinued the BF245.
However, BF245 is still an interesting transistor, that’s why it will be henceforward available in a SOT23 SMT package as the BF545. It is available in 3 groups A, B, C – sorted according to IDSS at VGS=0. Directly from our stock are available BF545A, BF545B and BF545C from company NXP (originally Philips). Detailed information can be found in the BF545 datasheet, as well as in the RF Manual document.
BF245 – the legend is leaving, the successor comes - [Link]
After our recent post about the commercial semi-conductor tester we started a discussion about building a similar open source project. What came up is this AVR based transistor tester (machine translation) by Markus.
It’s built around an ATmega8 IC that interfaces with a standard HD44780 16×2 character LCD. The circuit that does the testing is simplicity itself. Three pairs of resistors are connected to 6 pins of the microcontroller, and each pair is connected on the other end to one of the transistor pins.
The theory of operation is also relatively simple. The microcontroller cycles through different patterns on its output pins until a recognizable pattern is read on its input pins. It supports a very large range of devices:
- NPN and PNP bipolar junction transistors.
- P and N channel, enhanced and D type mosfet transistors.
- P and N channel JFET transistors.
- Common anode and common cathode dual diodes.
- Two diodes in connected in anti-parallel or series configuration.
- Single diode.
AVR-based transitor tester - [Link]
There is no doubt that Long-playing (LP) record albums are not for everyone. Some just don’t like the clicks and pops (more so with old vinyl records than new ones). Others don’t like the fact that you have to get out of your seat to turn them over or that you need a turntable and cartridge. Luckily turntables and cartridges, even very good ones, are not expensive these days. Then there is the requirement of an RIAA phono preamplifier.
With the phonograph cartridges only delivering a few millivolts an additional high-gain preamplifier stage will be required. Also when LP record masters are produced the bass is removed from the music to make cutting the master easier and the grooves smaller. The phono preamp has two jobs then: to amplify the small voltages coming from the cartridge and to re-balance the bass against the other frequencies (RIAA equalization). Both tasks are not hard and a few dollars of simple electronic parts is all the required to build a good sounding phono preamp. Or you can take the consumer approach and purchase an inexpensive preamp or pay $10k for a top of the line model.
JFET Phono (RIAA) Preamplifier Kit - [Link]