Upgrade from heat belching 5U4

[Chad Hauris]

5U4's are pretty reliable...have had hardly any failures from them. Some have been destroyed by shorted caps further down the circuit, though. Don't really feel there is a need to replace rectifier tubes with solid state.

Actually 5U4 and other filament type rectifier tubes are pretty "instant on"...as soon as you can see the filament lit, it's working (usually within 5 seconds). 5AR4 and similar types with a cathode sleeve warm up as the same rate as amplifier tubes.