Yaesu FL-110 modification for 5W drive


This pre-WARC 10 - 160 m band solid state all-mode linear power amplifier with low-pass filtering on nine bands was produced for the Yaesu FT7 and FT310S/SD QRP transceivers.


With this modification («fig) your QRP rig (FT-817 etc.) will put out the amplifier's rated 100 W. It will work into a 1 : 1.4 VSWR (SWR ≤ 1.5) when resistors of the input attenuator are removed and replaced. In addition it will allow 5 W drive to full output. It does work on the WARC bands with slight decrease in output power due to the low-pass filtering in the unit.



TEST WITH UNMODIFIED FL-110 (5 W drive and 13.8 VDC)

13.8 VDC

160 m

80 m

40 m

30 m

(20m LPF)

20 m

17 m

(15m LPF)

15 m


(10 m LPF)

10 m


60 W

70 W

80 W

105 W

105 W

60 W

80 W

60 W

55 W


I completed the mod suggested by Frits, PA0FRI and indeed the power required to drive the FL110 to 100 W output is now in the region of 5 W.

Just a word of warning when uses this amplifier with a FT-817. Used in the RF detection change over mode, this set-up lasted about 5 min before the '817 PA module blew!

I guess the change over time of the amplifier relay was enough to leave the '817 output unterminated, and with no effective high SWR protection in the 817, caused the PA to fail.

This is in no way due to PA0FRI's mod, but would suggest using hard switching from the 817 accessory connector to provide T/R switching for the amp.

73 Steve G4EDG