I'm hoping to use my new power amplifier during the next BATC activity weekend in June. First though a temperature test was needed as it's not very efficient. Testing power consumption a couple of weeks back it was using 85 Watts to generate 10 Watts RF output.
Following discussion with a knowledgeable friend I added a small Papst fan found in my spares cupboard. Advice was to have it cut in at about 60 degrees C; so I bought and fitted a normally open bi-metal device.
Initially I thought about buying some of the adhesive temperature strips and couldn't believe the cost; luckily I was loaned a measuring device with a probe which tucked nicely between the temperature sensor and one of the heat sink fins.
Starting at 20c which was shack temperature at breakfast time I fired up the amplifier with loads on input and output; at the same time running a stop watch. From an earlier brief run I had suspected the sensor and fan would be a safety feature only, I figured I would be OK with short overs.
It took 20 minutes and 40 seconds for the fan to kick in and the probe showed that it was exactly 60 degrees. After 2 minutes with the fan running the probe temperature dropped to 54 degrees; and 51 degrees after 5 minutes. Confident the amplifier is protected I'll run it in June.
There is one more issue to deal with; and that's where and how to mount the heavy lump without using long cable runs. Maybe the subject of another post.