Correct me if I am wrong, but I thought that blowing air onto hot tubes can result in "microcracks" and is not recommended.
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That's what it says in my Jadis manual as well. However, ARC does use fans in some of its models (I think my M-300/Classic 150s had them; that I can't recall entirely will testify that their noise was not intrusive), and I believe they make them for installation in enclosed rack/cabinet enclosures. You might want to check with ARC about this--what model amp do you have, anyway? You could ask ARC if a fan is really necessary for your application as well.
I put a Radio Shack fan on top of my Audio research VT 100 MK II and put a variable speed fan potentiometer from Home Depot. This lowered the fan speed and also the noise from the fan. This profect only cost me around $20.00. I put the fan so it blows across the amplifier to circulate the warm air away from the unit. Not blowing directly onto the tubes.
Hope this helps
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.
Usually the higher priced squirrel cage fans seem to be more durable as well as quieter. I've used these in high power HF tube amplifiers. In this case the bottom of the cabinet is pressurised and the air moves through a ventilated tube socket,up around a chimney enclosing the tube then out the top of the cabinet. This seemed to keep very big and very $$$$$ tubes happy.
Whether the air is 'forced' across the tubes or 'drawn' across the tubes makes no differnce since it is the temperature of the air that makes the difference and it is the same in both cases.
At any rate, if you can't hearthe fan then the amount of air flowing isn't high enough to be any 'danger' to the tubes, forced or induced.
Salut, Bob P.
Try End PC Noise for a wide selection of quiet fans. I have one I got from them mounted to the back panel of my HT system cabinet running 24/7 and it is inaudible. I power the fan with a 12V wall wart. Two cable boxes in the cabinet alone generate a substantial amount of heat around the clock, and with closed cabinet doors, I need to get rid of the heat buildup.
A comment that uses extreme brevity and a hint of irony is a "micro crack". Also, fans have been cooling tube amps in one way or another (suck? blow?) seemingly forever, and this is the first I've heard of micro cracks...I'm suspicious...I'm going to be looking for these everywhere now..."Hold still Marge...you could be standing near a tube with MICRO CRACKS"...