"Arfa Daily"

The 5U4 appears to be able to handle more current, but at a lower max
plate voltage. Also, the heater requires substantially more current. Might
be an issue for the transformer supplying it ?


** Very unlikely to matter.

Say the winding is rated at 5 volts and 2 amps to suit a 5AR4 and the copper
wire is gauged to give about 10 % regulation factor. Then the heat loss in
the 5 volt winding is 10% of the load power or about 1 watt.

If a 5U4 is subbed - the extra 1.1 amps will mean that 5.0 volts drops to
4.7 volts - well within specs for the valve.

The extra heat in the winding amounts to 0.8 watts - which is trivial in a
tranny designed to lose 15 to 30 watts as heat in normal operation.


...... Phil