Can I use a 40w PSU with a 50w tube

I went for the 50w machine, as it seemed a good deal.

It stopped working.

I am noticing 40w spec's are almost identical, but MUCH cheaper !

So, I need to find out if it's the tube or supply that is broken.

Can I buy a 40wPSU and use it with the 50w tube ?
Then if it doesn't work, I will buy a 40w tube.

Also in the future, the 40w will be cheaper each time I need to replace the tube (or supply)

I plan on using the poor little machine, all day every day, once it's working again.

Thanks in advance for any advice :)

Rich