Looking for Silent Fan Cooling f my ARC Tube AMP

Kevyo is right. You want a low-speed one for two reasons: prevent problems with tubes and low noise. Rogue uses one that is amazingly quiet and you may be able to find out from them what brand it is. And don't blow it direct on the tubes.

Do not allow the fan to blow directly onto the tubes as this will cause microcracks. Place the fan's exhaust away from the amp, which will allow the cool air to be "drawn" into the amp, thus enhancing the natural cooling convection effect to take place.

Yes definitely draw the heat away vs, blowing air into any component, tubed or not. A variac will reduce line voltage to slow down & quiet that fan, but don't use an SCR dimmer (even one for motor control) because they're typically electrically noisy. Lutron may be the exception but I've never tried one.

I don't get it. ARC's VT100 mk2 has a fan mounted inside the chassis. It's on the bottom of the amp, and I haven't checked to see if it is blowing up or down. However, what IS that fan doing besides bringing new air into the chassis for cooling? Is the VT100 mk2's design flawed in that respect?

I actually have my fan behind my rack circulating the air away from the rack. But I need a totally silent fan.