The AN758 Amp from CCI will be the benchmark for our amplifier. I received this amp kit from CCI last Friday. Natural convection cooling is out of the question unless you have a very large heat sink with a copper plate to move the heat from the heat source to the radiators. My goal is to enable 100% duty cycle operation. The HF SuperPacker Pro Version 2 used a copper heat sink with integral fan that worked well. The design for version 2 had the heat sink internal with the fan drawing air across the radiators and exiting the bottom of the box. There were several issues:
- The copper is hard to drill and tap.
- The fan was mounted upside down and wanted to come apart due being installed upside down.
- The airway had to be clear for proper ventilation.
I picked this heat sink fan combination: http://www.micforg.co.jp/en/c_fs80e.html
The thermal resistance target for a single heat sink cooling two devices would be: 100-50/150 = .33 C/W
I ordered the model FS8025PU which has the heat sink with mounting hardware and a quality 80x25mm fan.
The heat sink/fan combination attaches to the rear of the circuit board with L-brackets. The fan passes through a cutout at the rear of the amp. Looking at the rear, you would see one inch of the fan body. The circuit board of the amp would be mounted on four 1 inch standoffs. Air flow design and fan noise will be a major consideration.
I am planning on a DC/DC Converter Module based on the Linear Technology LT3782EFE high power dual phase boost converter mounted stand-alone to provide up to 50V for the RF transistors.
I am starting to build the AN758 Module and hope to have it in test this week. We will do our own artwork incorporating additional circuits as needed.
I have been getting some price quotes on dip silver mica caps used on the filter module. To get a decent price, we need to buy in volume. One manufacturer has a 1000 piece line item. I am shopping around for a reasonable supplier that will allow us to buy at least 100 sets of components at low cost.
73, K5OOR – Virgil