Oral History of Defence Electronics

R G Wells: AC - DC: Rectifieying the problem. The biggest problem was a rectifier to rectify the AC into DC without dropping it to a low voltage, because remember in those days we needed high voltages for the B supply, or anode supply, but in these days we bring everything down to small DC voltages; we needed to get them up as high as we could. That was a partial failure in that using aluminium foil again and oxidising one piece of it, or length of it folded over, with some weak acid and then using the two electrodes, one of clear aluminium and one of a zinc salt and aluminium, we could make a rectifier. We wouldn't be so audacious as to call it a rectifier now, because it had a reverse voltage of something like 30 or 40 volts, which wasn't exactly ideal, but for DC we had no option. The result was that I made a bridge rectifier but the only problem was that after 15 minutes the electrolyte began to boil, so it was really passing current in both directions but a little bit more one way than the other. So a single cell, an extra rectifier cell, was the only way I could close this down a bit, and some smoothing. This we achieved with part of a fish plate from the railway line which was being used at the aerodrome to move the dirt from one place to another by man-power, about six men on these, and the odd fish plate used to disappear anyway for various reasons. I dropped one off at the power station and asked the Chinese under my breath if he could cut it into three little sections which he did, he didn't want to know why. Then again using some palm oil and some bee wire which was in fairly plentiful supply, which we stole - it was a bit risky because the Japanese were cultivating a couple of beehives outside the wire and of course this wire used to disappear for various things unrelated to radio - and we put the palm oil along the wire stretched out and rubbed this palm oil on it, thickening it with a little bit of flour and then heating it; the flour bound the palm oil together and formed a fairly good insulation over the wire. Good, but lucky, and with a lot of travelling.

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