[Amps] AL-572 high input SWR

[K4RO Kirk Pickering]

A friend has asked me to look at his Ameritron AL-572.
The amp quit functioning about 7 months ago, after two
years of dependable service.  The amplifier was used
almost exclusively on 17 meter SSB. The symptoms are 
as follows:

Very low output - 100W on 20m-10m, 300W max on 160m-40m

Very high input SWR - > 3:1 on all bands, over 5:1 on 17 
meters. This is the SWR the radio "sees" looking into
the input of the amplifier.

My first guess was that a component (which is common to 
all bands) on the tuned input  circuit has smoked. A 
quick visual inspection does not reveal any burned parts.

Before I go digging deeper, does anybody have any
experience with this amp or suggestions on what may
have failed?  Thanks for any assistance.

-Kirk  K4RO