So I had noticed a while back, when developing my Icom (CI-V or band Data) to Yaesu BCD Band Data Converter that occasionally I could get 70MHz to show up as the band.
I always had it in mind to investigate this further. Today I set about finding the BCD which selected 4m (70MHz) and found it with all BCD lines high (Band A=1, Band B=1, Band C=1, Band D=1, ) great! On page 5 of the manual it shows the pin-outs, on BAND-DATA 1 or BAND-DATA 2 connect pins 4, 5, 6 & 7 together and then to 12v via a 1k resistor to get 70MHz. I noticed the amp would only allow LOW which I presume is to stop the PA’s overdriving into a non-optimized filter. The fact that LOW is only fixed when on the 70MHz band lends me to believe the designers know this and allow it. Now to the interesting part.
With 25w in I get about 240w output, rather useful as the UK limit is 160w. Id was about 25amps though which at 33v is about 825w and means it’s about 30% efficient but none the less the amp does it.
However with 65w in I was getting a peak of 500w. 35% efficient.
I’ve not run this long term so it’s all at your own risk! I did run it for about 10 minutes to keep the dummy load cool, but for UK legal this should be a good option to get you to 160w with about 20w drive.
Update 2/1/12: G6UW ran their Quadra for 2.5 hours in the first 4m RSGB UKAC contest of the year without issue. On air their signal was clean and caused us no issue, they were an S9+50 signal with us being less than 10km away.