Tim Lamb wrote:

TV aerial feeds. We have a loft 4 way amplifier. How likely am I to get
away with simply Teeing off the load end of one of those to supply a
5th. load?

Just fit a splitter on the shortest existing feed.

CPC:

AP00090 (uses belling plugs)
AP02109 (uses f plugs)
AP02104 (uses f plugs)

Given that you have an amp with gain to each output it's highly unlikely
the 4dB loss will make any difference.

Bill