BLA 350 HF Amplifier Repair

 The BLA 350 is a very popular, Italian made, linear amplifier for long distance radio communications in the 160-10 meter bands.

As the name suggests, it pumps out 350 Watts of HF power. I can hear you say "Ola, Ola, Coke-a-Cola". We have all heard the Italians blast out nonsense on the HF bands with wide spread splatter across most of the neighbouring channels. However, this little devil has very good filtering, which reduces spurious signals (SPURS) to the recommended minimum. 

Therefore, you can imagine the disappointment on the old man's face, when it let out the magic smoke and died and untimely death. Therefore, the case was opened and investigated for signs of damage.

It was clear to see, that the finals had expired. The MF150's used in this design are more that up to the job. Possibly a mismatch in antenna impedance had overloaded them. It is hard to say.

In the picture above, I had lifted the two upper gate terminals of the MRF150 MOSFETs, so that I could measure if they were dead or not. That is why the solder looks so nasty.

The finals were replaced by China knock offs. This was an experiment to see how good their copies were. After a few weeks, the parts were there and replaced.

The set was back in operation and delivering full power.

One happy owner - although we are both interested to find out how long the clones last.

Plessy PRC-320 Man Pack

 The Plessy PLC-320 was designed as part of the British Army's Clansman range of transceivers from 1978-2004. It saw service in places like the Rhodesian wars, Falklands and the Gulf war. I purchased this radio at a flea market in Ludwigshafen at the Ham Radio convention for €50.

It covers the full band of frequencies from 2 MHz to 30 MHz on AM, CW and SSB. It was typically issued down to a company level. It came with a 2.4 meter whip antenna or could be used with a long wire or dipole antenna. Clansman sets continued to be used by UK Cadet forces until 2014.

These radios make excellent portable Ham radio units. They can pump out 30 Watts PEP on high power or 3 Watts SSB on low power.

The sets support whisper mode, which allows the operator to talk in a very low voice in covert conditions, whilst pumping out enough power to be heard.

As you can see from the faceplate of this radio, it is an RT320-L, which means this a lower side band radio. These were typically manufacture in the old Yugoslavia, as it was called at the time. I also have the same set as RT320-U, which is upper side band. This was typically a British Army unit.

Ham radio operators have adopted the convention of using lower side band (LSB) below 10 MHz and upper side band (USB) above 10 MHz. Therefore, depending on which bands I want to work, I take the corresponding set.

The LSB set it best used at night in Europe and the USB set, during the day.

Shortly after acquiring the LSB set, it stopped working. These sets have an incredibly weak spot. The power supply unit that converts the 24V DC battery input to higher voltages (110V, etc.) usually fail. The transistors are hard to come by. Sometimes they can be repaired but most often they have to be swapped out.

You can see the PSU in the top of this picture. New, tested PSU modules are still available on eBay. I purchased on and swapped it out and the radio was back in working order. I am often out and about with it and the reception is just fantastic.