Nostalgic Memories of BD139 and VU2VWN QRP!

 Yesterday, I had mentioned that I was quite happy when I came across a BD139 transistor in a voltage stabilizer brought back after repair. That was because I remembered my early days in amateur radio, way back in 1985, when myself, VU2VWN (SK), VU2JOS and many others in this region used to operate the then popular VU2VWN QRP. As soon as I received my amateur radio licence, it was VU2NYR (SK), who gave me the circuit diagram of VU2VWN QRP and gave me guidance to homebrew it, tie up an inverted V antenna and come up on the band on CW. My callsign in those days was VU2JFP, with a grade 1 licence. My current callsign VU2JO was obtained after upgrade to advanced grade in 1988. My first contact on 40m after homebrewing the circuit was of course VU2NYR as we fixed a sked over telephone. When I started coming on band regularly, VU2VWN and VU2JOS were there regularly on air as well, and VU2VWN used to give guidance to fine tune my setup. Later I added a modulator to the CW QRP and started coming up on air on AM mode and it was easier to talk to them.

For anyone wishing to homebrew a VU2VWN QRP now, there are two webpages giving information. One is the site by VU2MSY (currently VU2MUE), which gives almost the same circuit which I had homebrewed. Another one is by 4S7NR. I found that the latter circuit is different from the one which I had homebrewed, mainly in the VFO (Variable Frequency Oscillator) part, which uses a couple of MPF102 FETs. The one which I had homebrewed had a couple of BFW10 in the VFO. Detailed instruction for the construction are available on the pdf at VU2MSY, written by VU2PCM (SK), I think. There is a disclaimer at the end that only those with valid amateur radio license should homebrew and use it. In the RF preamp section I had used SL100 and SK100 in the RF driver stage. Final RF power amplifier was BD139 with a heat sink. That was the stage where I had problem regularly, with BD139 packing off very often in spite of having a good heat sink. Maybe it was because I was not checking SWR in the initial days and coax was just 75 ohms TV cable and not 50 ohms cable. Yet, as BD139 was not very expensive and easily available in local market, it could be easily replaced and we could be back on air quickly if you have a surplus stock of BD139. Modulator stage had the TBA 810 integrated circuit which was quite popular in those days.

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