This is a project I started years ago. The EB63 kit was made by Communication Concepts and uses MRF454. I thought I might reference the Texas Star amps for parts changes. I got out of radio and never finished it. Any help is appreciated.
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EB63 amp adapted for 2SC2879
- Thread starter aeromojito
- Start date
Really really old. But if you already had the board for it, and wanted to assemble it, you can use the HG Semi MRF454 transistors. If you want to build a 2SC2879 based amp, start with a design that was meant for the 2SC2879, as turns ratios on the transformers and all tuning circuit capacitor values are likely to be way different, and bias current too. Nothing wrong with either Transistor, if you aren't looking to find the breaking point of transistors by driving the dog-doo out of them, then nothing wrong with the daily operation of a 2 x MRF454 amplifier, especially with proper biasing. I haven't used the HG MRF454 yet, but have heard they are great. I HAVE used the HG MRF 455 in one of my small amplifiers, was skeptical, but after probably 100 hours of use, still working perfectly, they were a drop in replacement. Some recommend a little bias current change (lower than original MRF454/455), but my amplifier was already biased pretty low, so it worked out fine.
I already have it assembled from many years ago. It actually does work but with less power than expected. I'll take a look on the oscilloscope but my meter says 175W PEP. On AM, that is with a 70W carrier. In other words, the peak power is not 4 times the unmodulated power. The bias is a little high at 1.3A but easy enough to change. I changed a few capacitors and the input transformer from 4 turns to 3 turns. Most 2879 amps I see have a 1:3 ratio on the output transformer so I may change that.
OK. I reduced the bias to .5A and took out 1 turn of the output transformer. Now it will deadkey 50W and peak at 225. I tried a 3db pi attenuator and it deadkeys 50W and peaks at 175 with a 4W input. Not bad.
I guess I'm still the only one who has attempted this. Since the last post, I changed the C-E capacitors to 120pf and added 2 attenuators. I also beefed up the power wires and a few other minor changes. I added a relay to the bias resistor. I tried a higher input and got up to 350W on the PEP meter. Since then, I use it when I need it and usually stay under 200 W.