Tony G0MQG Tips

MX295 2 metre conversion.

Some years ago, having read an article in “ham radio today” ( I think that was the mag the article was in) I decided to have a go at converting a Philips MX295 to 2 metres. The modification went quite well and I found that when rewinding the coils in the receiver front end, if this was done carefully to get these correct the receiver was extremely sensitive, probably because of the dual gate mosfet front end. I done several of these radios and some I replaced the prom with a UV eprom which I programmed myself with all repeater and simplex channels. However, because these radios were designed for band 3 (approx 200 mhz) I found the PA would oscillate when retuned to 2 metres and spent many an hour trying to tame it ith only partial success. The last one I converted I decided to have a different approach with the transmit PA. I removed the heatsink from the rear of the radio and removed the PA and driver transistors and associated components leaving only the rf in to the PA compartment, the pin diode switching and the 12 volt supplies to the PA and driver transistors. As the heatsink has a cast finish in the PA compartment I took it to a toolmaker friend and got him to machine over it for me to give a good finish. I then fitted a slab pa module (which I got from ebay) to the heatsink and wired this to the rf in, the 12 volt supplys as neccesary and the rf out after rebuilding the filter stage (copying how the MX 294 was done) this worked quite well and was stable and produced about 12 watts output – the maximum the slab I used could provide. This worked very well on 2 metres and even had ctcss fitted as it was used commercially so only had to be set to 94.8 hz for GB3NB, I used this radio for quite a while on 2 metres.

Tony g0mqg

Christmas 2017