Tube Preamp: How many tubes does it take to .................

McIntosh C220, with remote, with phono, total 4 tubes

’cool tube glow' out the top seems to be it’s claim to fame

http://www.berners.ch/McIntosh/Downloads/C220_own.pdf

One major differentiator is if tubes are used for just the preamp or also for the power supply. Lots of preamps, used to only use them for the amplifier section. Over the last decades there has been a movement to use tubes for both. So my Audio research preamp and phono stage (very similar topology and function) use 8. Two for power supply regulation.

How many? Well, I guess the designer decides, and that I am sure depends on the sound quality he is going for.

Decware Mini Torii has 10, 5 on each side

1 rectifier

2 Voltage regulators

1 preamp tube

1 power tube

It also depends on if you are using dual triodes or single triodes, and if you are using half wave rectifier tubes or full wave. If you are using half wave rectifiers you can use 4 tubes for a full wave bridge, you can't do a bridge with full wave rectifiers.