by 5B4AIY » 26 Feb 2013 16:44
Hi, Larry,
The TRX-1 PA uses the IRFR110 power MOSFETS, and these are fairly rugged devices. When mounted on a PCB, as they are in this case, the maximum disspation is limited to 2.5W. Assuming an overall DC to RF efficiency of 50%, fairly typical for small solid-state amplifiers, then with 10W DC in and 5W RF out each device will be at its maximum dissipation.
Under SSB service the typical peak to average ratio is of the order of about 5:1 so the amplifier will operate fairly cool in this mode at 5W PEP O/P. When operating CW the duty cycle is significantly higher, and in this mode it would be around 50%, so, although the output stage will operate hotter than with SSB, it is still within the maximum ratings of the MOSFETS.
Not so with RTTY/PSK31. These modes use a 100% duty cycle, and in this case in order to keep the dissipation and temperature down you would have to run the amplifier at no more than about 2W output. Providing you observe this derating, then you should not have any problem.
73, Adrian, 5B4AIY