[Clydeuk]

I wouldn't bother going out and buying a load of capacitors as you will not hit upon the solution just replacing caps. You need to get a multimeter and measure across the horizontal output transistor, I am convinced that will be short-circuit. If you're not confident with the circuitry you really need someone to help you. Simply replacing capacitors is likely to cause more harm than good due to the possibility of human error. Also as mentioned above the third harmonic capacitor will be a critical value and you won't get that locally. You can't just replace this with something close in value, it has to be exact.

If there is a short across the B+ such as a failed transistor then it will cause the power supply to trip the way you describe.