Hi nice to see them, I have a coupleI built and they were a good value for money at the time but that big transistor failed and I gave up on them. I still have a few ZN 409s though left over from when my eyesight was better.
My first home job esc was the Pompey published in RC &E magazine. I built 2 of these, they had an H configuration of OC 29s (I think) with the motor in the centre bar of the H. But you dropped 2 lots of 0.7 volts across the emitter and base junction so they got a bit warm, mine were mounted in a small tobacco tin with the tin as the heat sink.
The Pompey pre-dated the Maplin as it had an integrated circuit in a transistor can with 6 legs. Later of course there was a BEC circuit published in Model Car magazine (still use them). In those days the BEC circuit was in with the rx. This was a neat little circuit using a zenor diode as the voltage control.
If anyone is repairing old esc's I have a small supply of OC 29 and 36 just drop me a PM. (no charge)
Next came a neat little circuit which when there was a maximum speed called for from the Tx then this circuit would by-pass the amplifying transisitor(s), so giving you a zero volts drop and the power transisitors could cool down.
Now with FET technology and more there is so little power consumed by the esc that heat sinks are no longer needed.
Happy days!