Experimental low power amplifier for 2190m longwave

I salvaged some potentially useful parts from a faulty pc power supply, e.g. bridge rectifier, schottky diodes, heatsink, fan, chokes, transformers. The 12V-0-12V, 5V-0-5V output transformer typically operates near 40KHz. I thought of using it for the output matching transformer in a low power transmit amplifier for the 136KHz, 2190m longwave band.
My design is based on the very cheap, ( half a $ ), TDA2030 class AB audio amplifier ic, which has a bandwidth of 140KHz.
The circuit is experimental. I was curious to find out if such an amplifier would be useful for 136KHz, despite using some untypical, possibly 'unsuitable', components.

I built the amplifier on a home-made printed circuit board, 70 x 100mm. The ex-pc transformer, ( yellow & black ), is on the left. The TDA2030 is mounted on the ex-pc heatsink. ( Pcb artwork and the circuit schematic are available from me on request ).

Fitting the circuit board inside the old pc power supply box, ( cover not shown ), with its original 12V fan, and adding a LED, rf and dc connectors, completed the construction.

For testing, I powered the amplifier from a +13.6Vdc power supply and connected the input to my frequency synthesiser tuned to 137.8KHz. With the input attenuation set to minimum, and the output terminated in a 50 Ohm load, the measured voltage gain was 41.75dB. Output power was 3.5W.
I could now either connect the amplifier directly to my longwave antenna and make some very low power test transmissions, or use it as an intermediate amplifier stage in a much more powerful transmitter, yet to be built.

Modifying PC PSUs - finishing off

Recently my electronics workshop in the cellar has become just warm enough to visit to complete the modifications. Since the posting on 26th January, I have chosen to use 30 Amp Anderson Powerpole connectors for the red/black 12V output terminals; fitting a LED 'power-on' indicator and non-slip rubber feet underneath completes the work.
( Thanks Richard for donating the original. )

Putting old computer power supplies to good use

ATX type switching power supplies which have been removed from redundant computers can be easily modified to provide useful +/-5V and +/-12V ( also not so useful +3.3V ) DC fan-cooled bench supplies delivering around 300 watts in total. Voltage regulation of all rails is controlled by the regulation of the +5V rail, which needs to be permanently loaded with a resistor of about 10 Ohms rated at 3 to 5 watts. The power unit I am modifying is almost complete; just needs some nice red and black output terminals to be fitted and then it's ready to take its place on the workbench.