OBSERVATIONS From Scotland                 GM1SXX                                                 03/04/2007

For the next part of the puzzle, finding a PA for the MA 1720, I have a solution.  An HF kit amplifier called an EB63. This is a kit by Communications Concepts, a US based company.

http://www.communication-concepts.com/default.htm

Here's what the designers say. The EB63 amplifier has an output of 140 watts (PEP) over a frequency span of 2-30 MHz. The amplifier uses two MRF-454 transistors. These transistors are specified at 80 watts power output with 5 watts of input drive, 30 MHz and 12.5 Vdc. The MRF454 is used because it is a readily available device and has the high saturation power and ruggedness desired for this application. The amplifier will accept Single Side Band (SSB) or Amplitude Modulation (AM) without external switching. A carrier operated relay circuit (COR) is on the same layout to make this an easy amplifier to add to any suitable radio with an RF output of 1-5 watts.
 

SPECIFICATIONS: Frequency Range 0-30 MHz RF Input Power 1-5 watts RF Output Power 140 watts Input Impedance 50 ohm Output Impedance 50 ohm DC Input Voltage 13.6 VDC Input Current 22 amps (typical)

The EB63... based on a Motorola Application Note

I bought one at a rally some years ago because the price was right. I think I paid £25 for it at the time. Definitely a bargain. It needs a watt or so of drive so I may need to build a small linear amp to raise the 200mw of the MA1720 to a suitable level to drive the EB63. It can go in a box with the PA and filter plus of course a 25 amp PSU to drive it. There is  a carrier operated relay on board.  I'll change that to hard switching via the MA1720. Safer and more sensible.


73 Al.