Power mod for the SSTRAN AM transmitter
Posted on May 9, 2007
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Got your attention didn’t I? No, this is not about getting a bigger signal from the SSTRAN, it is about a nice modification to add a power on/off switch. There is no harm in running this transmitter 24/7 but since I only need it a few hours a day it is my personal preference not to throw a dead carrier for no reason. There is no legal reason that you can’t, I just choose not to.
So, after sitting and staring I came up with a way to add a power switch to the device. I didn’t want to mess up the nice front panel appearance and I hope all will agree that I accomplished this objective.
Please note that it takes some skill to unsolder components from a PC board without damage and if you are not comfortable with this you might either seek help or abandon this project.
Vigorous shaking of my junk box yielded a subminiature panel mount toggle switch (very similar to RS cat #275-645) which will mount in the front panel if the power status LED is removed. Here’s a step by step description of the surgery.
- Open the case and remove the front knobs, unscrew the circuit board, and remove the front panel. Drill a hole in the front panel which will provide for mounting the switch using the LED hole for placement. Just enlarge the LED hole to fit the switch.
- Remove the circuit board and unsolder the LED.
- Solder two hookup wires (about 8″ worth for each) to the switch so the circuit is closed when the switch lever is up. Install the switch on the panel and check for clearance when the panel and board are in position. It should be OK. If not, gently bend the electrolytics out of the way. Install the switch in the front panel.
- Locate a position for the LED in line with the “POWER” label about 1/4 inch to the left of the letter P.
- Drill a new hole for the LED. I made it a bit undersized so the LED press fits. If the LED is loose, a spot of glue can be used later but it will make removing the panel difficult. It is best to make the hole a bit small for a press fit. An undersized hole can be easily reamed larger with a small screwdriver to get a good press fit. Ream from the back of the panel so the slight taper resulting from the screwdriver reaming will work to advantage.
- Once the fit is right, remove the LED from the panel. Resolder the LED to the board using short pieces of hookup wire ( about 1″). Watch the polarity and let it dangle for now.
- Facing the front of the board, unsolder the right end of L2 from the board, lift the inductor end, and straighten the lead. I chose this point in the circuit to break the power stream so I didn’t have to butcher the board.
- Cut the switch wires to fit and solder one into the hole in the PC board where L2 was connected. Solder the other lead to the flying lead on L2. Position L2 back onto the surface of the board and make sure the wiring doesn’t short.
- Install the front panel, mount the board to the bottom of the case, and press the LED into the hole. Reassemble the unit and you are done.
The front photo should help you decide if the modification looks OK and give you some idea of how I did this.
I hope if you do this you will be happy with the results. I also hope Phil will forgive me for changing his fine transmitter.