Running a fan to cool amplifier any ill effects?

if the tubes run slightly cooler this may extend their life a little.

I would be more concerned about the electrical noise the fans motors could be dumping into the mains. If you have a different circuit for the hifi or conditioning of some sort you could be ok. As long as the fan motors are good quality it may not a problem anyway. Lets face it many amps use fans internally.

Can you hear the fans in your listening room?

Unless your amplifiers are in a confined area, you should not have to worry about heat. VAC designs their products with heat dissipation built in and normal air flow around the tubes will provide adequate cooling. Fans are not necessary and may introduce unwanted noise. I think you are fixing something that isn't broken.

Thanks for the responses so far....the fans are on a seperate cicuit than my audio equipment. I checked out the noise level...not a problem. I realise that the amplifiers are well designed units....the transformer housing which is thick heavy metal gets hot enough where I can only heep my hand there for about 3 seconds. So to me I just feel better if the cooling will disipate some of the heat generated. If it extends the life of the tubes....even better...though it might seem unnecessary or overkill.

Try to prevent the fans from touching the chassis .
The fans could induce a low level vibration and a subsonic that the Amp will carry. Perhaps making your amp work harder.
If you can, put the fans on a stand blowing on the Amp.

I have two mono blocks that are fan cooled. Because the design was for rack mounting, and the close proximity of the 8 el34's per amp, this was a must. The fans blow directly across the tubes. The original fans were ac driving, and I replaced them with very quiet dc driven types with their own supply system. Each fan is on a rubber mounting system to help isolate their vibration(which is minimal)from the chassis. I believe that this prolongs the life not only of the tubes, but other components inside the chassis. These amps are now 45 years old! I believe if you check around, you will find that most "experts" will tell you that excess heat will age a tube about as fast as anything(ok over biased etc). Some complain of the noise, but I have been able to screen this and slow the fans such that it doesn't bother me........