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               Legal Limit - Solid State Amp Photos

Each "Pallet" has 4 MRF-150 FETs, takes 6 watts drive, and produces 600 watts output

This amp will mount two pallets on each copper heat spreader. There will be a total of four pallets. 

Click on photos to enlarge in separate window.


Milling shoulders on solid copper heat spreader               Drilling / countersinking holes for bolts



Pallets are 3  5/8 X 5  1/8 - Copper heat spreader is 9 X 5 X 3/8 - note 1/2 inch channels along edges

 and center to allow mounting to aluminum heat sink. There are 24 holes drilled and hand  tapped 

for 4-40 screws on each copper spreader  to hold FETs and boards.



Close-up of thermistors, crimped &  soldered                                          Thermistor mounted to FET.  

inside ring terminals                                                                                        Red wire connects to lead for BIAS tracking


Four FETs in place, ready to be soldered to board.                                Closer view - holes in channels are counter-sunk,

FETs must be mounted to heat spreader first, then                               to allow for 10-32 socket head  cap screws to mount

soldered, to prevent damage to FETs                                                        copper heat  spreader to aluminum heat sink


Views of Finished RF Pallets

To simplify changing boards, all inputs/outputs now have connectors


BNC connector added for RF output                                                          SMA connector added for RF input 


BNC mount fabricated from Brass sheet                                                    PowerPole® connectors for DC (black & red) and bias (purple)


                                                                                                        RG-316 cables,  RF from splitter to pallet input

                                                                                                                                     cut to +/-  1/32inch                                                                                                                                                          


New Views of RF deck / heat sink

Deck is 10.5 wide X 6 tall X 12 long. Base of sink is 3/8 thick aluminum

Sides and ends are 3/16 thick aluminum

Weighs 29 lb before any parts or copper added

4 - 120mm, 12V fans will provide cooling

All bolts/fasteners used in project are stainless steel 



View from end of heat sink assy, one fan removed             Mounting copper heat spreader to heat sink


Nine #10-32 screws will insure a snug fit                                   Mounting the 4 way splitter and combiner to heat sink

 and good heat transfer


One side complete, once standoffs are added,                          Need to add balancing resistors for combiner / splitter

2 additional pallets will be mounted to other side                   and Selco's for temp sense to run fans



A home brew Icom® band decoder will be built and incorporated. (DONE, 7/29/09) A front panel, 
7 position switch will allow manual or auto selection of filters. LED's will give visual indication
of filter (band) selected.

A stepped speed control for fans and the band-pass filter boards are next items to work on.
On advice from K5RUS, went with a thermistor based controller, providing totally variable
(quieter) speed control, with a single Selco® override for full speed if necessary.
(DONE, 8/11/09) (re-built w/ heavier duty parts for better long term reliability, 8/22/09)

I've decided to incorporate multi color LED bar graphs to monitor forward and reflected power,
similar to what you see on Alpha® amps. LED display will be about 4 inches long, large enough
to actually see. Several LM3914 IC's along with necessary LED's were acquired to build the 20 led
(green / red) forward power bar graph, and the 10 led (green / yellow / red) reflected power bar graph. 

Designing and building opto-coupler based keying circuit. Sensor for "overtemp" will disable
keying and Bias, and turn on front panel warning led. (parts acquired, 8/24/09) 

Just after the last step was completed, a tree took down my main tower and 6 antenna. Even the best amp in the world won't help with no antenna, so since that time, I have focused on building tower(s) and stacked mono-band yagi's. Once all the outside hardware is in place, I hope to return to the amp project.