It’s not often we see a tube project here, so [Helge Fykse]’s PCL86 transceiver is a welcome find.
If you know anything about the European Pro-Electron device naming system you’ll be familiar with it as it applies to tubes. The first letter denotes the heater specification, for example “E” is for a 6.3 volt heater. Everyone wants the familiar 6.3 V devices, but they have a set of cousins which often pass unnoticed. “P” tubes have a 300 mA heater designed such that all tubes in a device could be connected in series at the same current. Of those tubes the PCL86 is a mundane example, filling the function taken in the semiconductor years by the LM386. It’s a small-signal triode and a power pentode in one device, and it’s an audio amplifier. Every 1960s TV set in Europe had one, and thus it’s a good choice for experimentation.
This transceiver is a conventional crystal oscillator and power amplifier on transmit, but with a flick of a switch it transforms into a direct conversion receiver in which the triode becomes oscillator and mixer while the pentode becomes an audio amplifier. It’s simple, and the video below the break explains it in great detail. We’re not sure whether or not it could unintentionally radiate in receive mode, but we’re guessing the energy would be tiny.
A simple tube project can make an interesting departure from modern surface mount electronics, so if you get the chance we’d suggest you try one. If you don’t need a transceiver, an audio amplifier is the archetypal PCL86 project.
