['LIVEWIRE?']

Thanks, Lawrence, for explaining the function of that semiconductor diode. The diagram, t.b.h., isn't that clearly drawn in some ways. Maybe that's why I had difficulty working out what the diode (4000x?) was there for. Speaking of diodes, a note on the diagram states that, in some cases, 2 x 1N4007s are used instead of the GZ34, but only in amps fitted with EL34's. Having looked at the data for '34s,, 5881's, and KT66's I can see no reason why 4007's (or other semiconductor diodes) shouldn't be used with any of the 3 o/p bottle types. If necessary 3Amp diodes (1N540x) could be used, with appropriate series resistors, of course.