PA-47 with Fan Control

Today I breadboarded a FAN Control circuit for my PA-47 RF Power Amp (see previous post). I used a simple NTC Thermistor for the sensor, which will be attached to the FET on the Heatsink. The FAN Control circuit also supports a slight temperature bias when the TR Relay is activated.

The Thermistor can be seen attached to the FET

The breadboard FAN circuit has be running for several hour - working as expected, it cycles the FAN ON and OFF (with speed control) as the Beacon Exciter transmits on its six minute schedule. The RF output is connected to a dummy load, as I have not looked at the PA signal on a Spectrum Analyzer yet.

The Chaos of the Bench
Testing in Progress

My goal was to build the new PA with the additional FAN Control circuit small enough that it would fit the same 1 x 1.5 inch layout of the current PA-47. I had to rearrange a few parts to make it all fit.

While doing some experiments with a new layout with DipTrace, I tried laying it out as a four layer board. Four layers makes the circuit layout much easier. but it would be a lot more expensive ( about 3 to 4X ).

New two layer PA-47 boards with Fan Control are now on order.

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