Updated layout & tricks

The layouts and schematics posted here are the 'original' ones: if you decide to build an amp based on these layouts, please take note that you should at least update the wiring of the power cord (use a three prong cord and remove the deathcap). The wiring of the heaters is also a very good candidate for a more modern approach. See this layout from Weber for an idea:

Furthermore an artifical centertap from the PT can do a lot to reduce heater hum (even if your PT has a centertap) in SE amps (but I like it in PP amps as well). You can wire it from the heaters to ground using 100R resistors like this:

You can also use dc-elevation on amps with a high cathode voltage when you wire in an artificial centertap: use two 100R resistors and run them from the heater connections on a powertube socket to the cathode (pin 8) of  that same socket. Heaters (ac) now float 'above' the dc you add form the cathode.

For more info, please visit the website of Merlin B, valvewizard.co.uk. He has a wealth of information available. 

In any case, do not use both the CT from your power transformer (if it has one) and an artificial centertap. And finally, no matter what you do with your amp, be very careful: the voltages inside an amp are lethal.