[Elecraft] [K2] K60XV Low Output at Low Voltage

[Steve Kavanagh]

I noticed this past weekend that my K2's transverter output level was lower than the nominal 1 mW it was set to when operating from the car battery with the ignition off.  I confirmed this behaviour today, with about a 12.2 V power supply voltage to the K2.  The power control of the K60XV worked fine up to about 0.85 mW but was unable to go higher when the power knob was turned up to maximum.  There's no problem when running from a 14 V supply.
 
The only transmitter stage running from the unregulated 12 V rail (in transverter mode) seems to be the buffer U9 - does anyone know if this stage is running close to its compression point and if this behaviour is normal ?  Its gain appears to be fixed by resistors and one capacitor and shouldn't be very voltage-dependent.  Or do I need to look into tweaking the 10-12 m bandpass filter to get a bit more margin ?  Or maybe adjust/modify my transverters to run from a lower input level ?
 
73,
Steve VE3SMA