Lots of ‘Repco’ type valve spring compressors don’t work for Trumpy heads and you don’t really need to fork out the coin for one if you have an ordinary carpenter’s clamp. Cut a piece of 25mm water pipe 75mm long. About 2/3’s of the way along drill a 10mm hole right through the pipe. Cut a slot 15mm wide at the end of the pipe back to either side of the 10mm hole – see photo.
It’s probably a better tool if you weld the tube to the clamp to make sure everything is secure but I’m a lazy bugger and I don’t have a welder. Maybe weld a plate to the base of the tube and fix it to the clamp with a central screw? The bottom of the clamp goes to the valve head and the split tube to the valve spring – not much room to get the collets out but it does work okay.