[Red to black]

Not necessarily, the fuse could have blown on its own on these, or dry joints could have been responsible in any event.

Before you buy anything first prove that the items are actually faulty by testing and voltage measurements.

The Zener diode I mentioned became a stock fault late in the day for these sets and has also caught many an unwary engineer out at least once before.

The first time I had it, it did take some tracing! with many other parts replaced before I realised (finally!) what was wrong.

Obviously make sure the large cap is discharged first! the Thyristors are not easy to check cold (best by substitution) unless S/C of course but rule everything else out first. Check the 4 bridge diodes cold (ie.dead /not powered up) The main HT line on this set is 156 Volts so check that too.