Hi all,

During testing something went wrong: result no output. At first it operated
flawless: a good 140 W out with 4 W in (FT817). It must have gone into
oscillation because the resistors R1 and R2 were smoked. I used a transfer
relay without further precautions (I know, never ever again: I will make the
bias circuit switchable). Now the funny part: bias is easily adjustable as
ever. Remove the load and it oscillates with heavy harmonics at about 2 MHz,
taking about 3 amps. Iquiet about 200 milliamps. Both bases: +/-0.75 V. My
guess: one of the finals is blown (base bonding evaporated). So I have to
exchange them. Before disassembling this unit I'd like to get some advice
and comments. Is it normal if one transistor fails that all output is gone?
Or did something else fail (as well)? Then: if I need to buy new
transistors: do I need to buy MRF 454 or MRF 458. The latter are in my
actual amp (and seem to be cheaper) and said to similar but I don't have a
data sheet.
Please advise,
Harke