It's on the driver transistor right near the final.
Also dropping the drivers bias a couple of ma to the bottom range of spec helps stop the oscillation.
Bottom left corner of this schematic, http://www.georgiacapital.net/ke4sls/htx100/pg_0061.jpg
Stan : Great suggestion! However we had allready tried increasing the cap value on neutralizer for both finals with no change. This thing has driven me over the edge and after a lot of hours looking for out of value caps, leaky switching diodes & or xistors, I discovered that the bias line for the finals was actually going negative when it started oscillating. Since the output filtering ( lowpass filter) was centered around 54 MHZ, & that was what the freq counter said was the freq of osc, I went backwards through the whole ALC loop trying to find something wrong. Nothing there. Tried running 40 ma on both finals & lowering the output levels with the Hi/Lo output adjusts & actually made it a little more sensitive to start oscillating! Finally gave up, put it all back to "spec" settings & added a 2.2 uf cap on the 2nd final bias adjust pot on the pot side of r149, 82 ohm 1/2 watt,& has not locked up again yet! Only side effect from this is a slightly overdriven audio . Nothing excessive, just have to not get to loud into the mic. Thanks again for the help! 73 !! KJ4RZY AL