[Kenwood] TS-440S RF Power decreases at Higher Freqs

[W0rw at aol.com]

My TS-440S has an RF power output that decreases at higher frequencies.
This is intermittent, after a few hours of operation it works OK.
No mechanical or vibration symptoms (i kicked it and nothing changed).
The output is connected to a dummy load (with the ATU out of the circuit).
The output power decreases with frequency increase:
7MHz 100W
10MHz 90W
11MHz  80W
12MHz 70W
13MHz 50W
14MHz 40W
15MHZ 30W
16MHz 30W
21MHz 20W
28MHz 20W
Has Anyone had this problem before ?
Maybe one of HF drivers has a problem...
Right now the loss is stable enough to trouble shoot.
It is a 1989, s/n 9120627, i have all the books.

Paul  w0rw at aol.com