A shot of my old 2 meter amplifier (W0KT called it a telephone booth due to the cabinet it is in), converted from a Quintron QT-8505 PA. 650+ watts out with about 5 watts of drive. I normally use a 4 dB pad before the driver board. I can probably remove the driver board and use a full 25 watts of drive and still get full power out. The original design used a preamp/IPA board and the exciter only provided 200 milliwatts of power. Power supply requirements are 28 VDC at 70 amps and sits below the PA chassis. The fans draw air in the front of the power supply and blow up the fins on the back of the PA chassis. The heat sink is so massive I never bother to run the fans (too noisy as well). A very simple conversion and with the paging market all but done, it is possible to find used transmitters for a reasonable price. The RF devices are all MRF174's. Note the simple 3-way spitter and the complicated 3- way combiner! The 200 watt PA boards are 2 MRF174's in a push/pull confuguration. These devices are a FET and act a little like a tube. Bias them to about 750 mA of current per device, somewhere around 4 VDC. The bias actually goes negative during standby. The lower section is the low pass filter and the directional coupler. The amp is fully metered and the cast chassis is an immense heatsink! I'll add a photo of the control and meter compartment later. 
| 
