I have a Henry SS750HF solid state amp. It has four boards, each with a pair of
2sc2879's. The following happened:
1) I applied drive on 28 MHz when the filter was set for 14 MHz (he who is
without sin may cast the first stone). After I finally noticed that there
wasn't any output, I selected the correct filter and found that the output was
much lower than normal. Investigation revealed that the E-B junction of one of
the transistors was SHORTED (all of the others were OK).
2) I had a spare board with transistors from the same lot as the others. I was
99% sure that the board was good. I swapped it in and applied drive (on the
same band). Same result -- low output. Investigation revealed that the E-B
junctions of BOTH transistors on the board were OPEN. I decided that the board
hadn't been any good in the first place, and I ordered a matched pair of
2sc2879's from RF Parts.
3) I put these transistors on the original board. I checked the transistors and
adjusted the bias so that each board drew 250 ma in idle. Then I applied
drive. Result: low output. Investigation revealed that the E-B junctions of
the new transistors were now OPEN.
I've looked at the splitter and combiner on the theory that maybe something was
funelling all the drive to one board or there was no load, etc. These are very
simple units and nothing appears to be wrong. heat is not an issue; it happens
I've converted about $85 (including shipping) of transistors into sand and I'm
not prepared to spring for any more unless I can figure out what's going on.
Does anyone have any idea? Right now I'm in a mood to entertain offers to buy
the unit as is, too.