Making Output Transformer, T2 of VU2EVQ HF Linear Amplifier

Instead of two RF1000 toroids in the VU2EVQ linear amplifier design, I am using a single BN43-7051, which is a binocular toroid bought from VU2PTI as RF1000 was not available. Primary ‘winding’ of this transformer is being made by copper tubes used in refrigerators. I got it from a refrigerator spare parts shop in the city. Two pieces just enough to fit inside the two holes of BN43-7051 forms the primary winding. Took the toroid to the shop and got exact size of copper tube which goes inside and got it cut exactly as well from there.

One end of each copper pipe is connected to the drain of each IRFP150 MOSFETs. The other ends of the copper tubes are shorted to form the ‘central tap’ of the primary winding. They are connected to the bar on the PCB to which RF Choke is also connected. In effect, that will go to the positive power supply line through the RFC. 18 SWG copper wire was used for the connections. Had a very tough time soldering them to the copper pipe. Needed 100W good quality soldering iron and a lot of effort. I went through several cycles of soldering as the solder joints on the copper pipes would not hold!

Secondary winding is three turns of 19 SWG insulated copper wire used for submersible pumps. One end of the secondary winding goes to the low pass filter (LPF) and the other end goes to ground bar just beyond the bar on which the central tap of the ‘primary winding’ is connected.