[SCCC] Amplifiers

[Bill Kendrick]

I have a KPA 1500, one of the first. It was a rough start because of an
intermittent short in the 6 meter yagi. They did modify the fault detection
and it kicks out much faster now. The only issue I see is it gets hot. Since
there are only two devices the heat is dissipated in a small footprint. The
amp heats up really fast. In FT8 I put it in standby when it hits 70C. It
normally runs between 45 and 63 C. Even in CW when I contest the amp hits
70C when I am running Qs. The fans have 3 levels and at 70 it sounds like
the amp is going to take off and fly around the room. Otherwise, it is
pretty quiet. My Astron 50 amp switching power supply is the real noise
maker in the shack. You can run 1500 on FT8 but why? Typically on 6 meters
800 watts will do for the Es European opening. Finally, to hit full output
you often have to draw 60 amps and the fault limit is 62. On 40 meters if
you move frequencies the VSWR changes and that number is often exceeded.
Even if it isn't the output power fluctuates with frequency. I find myself
operating at 1300 watts to avoid any issue. No big deal. If you want to hit
it hard you just remember to back off when you move to another station.
 
Now, the Expert 2K-FA is probably the most reliable solid state amp on the
market. You can break it but you have to far exceed the spec limits. Several
guys on DXChat have it and they say it never exceeds 40 C or so. It has
other features like multiple antenna ports and it is quiet enough. It has, I
think, 8 transistors in 4 modules so the heat is distributed. The drawback
is that you can not run full power in digital modes. It throttles itself
back to medium (they have three bias settings) after a certain time period.
Still, not a big deal!
 
Bill
N6RV