Output transformer - to eliminate the output transformer we stick with a line amplifier design. Line amplifiers, unlike power amps, can be capacitor coupled. We still get to experience the joy of tube sound, but without the burden of driving speakers directly with tubes. In the picture below you can see a Mr. E.Z. Tube connected between a PC line-out and cheap PC speaker amplifier. My next instructable will cover the construction of a 'gainclone' op-amp power amplifier to pair with the Mr. E.Z. Tube.
Power transformer - The vast majority of tube amps use a transformer connected to mains power (AC) and a rectifier circuit to produce clean high voltage DC for the tube. This heavy chunk of metal and wire is expensive and dangerous. The rectifier diodes and capacitors alone are a whole project. Mr. E.Z. Tube uses a 240 volt switch mode power supply I originally designed for nixie tubes. The SMPS is simple, with the option of battery operation!
For a detailed overview of the SMPS operation see my SMPS instructable for nixie tubes:http://www.instructables.com/ex/i/B59D3AD4E2CE10288F99001143E7E506/
The Mr. E.Z. Tube SMPS has a few enhancements to eliminate switching noise:
1.A larger inductor (1.2 amp continuous rating).
2.A soft recovery rectifier diode (BYV 26C) was used.
3.Two large output capacitors and a choke were added to the HV output.
4.Updated firmware with high voltage 'enable' switch.
With these enhancements there is VERY LITTLE switching noise - it is only noticeable with no audio playing and power amplifier volume at 100%.