Fans on tube amps

Bill Duncan · From: Lenoir, North Carolina, USA

Are fans used for cooling purposes commonly used on tube amps?
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Richard Sinkler · From: aka: Rusty Strings -- Missoula, Montana

Every tube amp I have ever seen doesn't have cooling fans.
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Craig Schwartz · From: McHenry IL

interesting , I suppose there must be a reason for the extreme heat on those glass tubes at all times.
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Jack Hanson · From: San Luis Valley, USA

Someone will correct me if I'm wrong, but I believe some of the early Ampeg SVTs had cooling fans inside.

Jon Light (deceased) · From: Saugerties, NY

My Tone King Comet is a 4 x 6V6 amp and it has a fan.

Lane Gray · From: Topeka, KS

My Super Twin has one, but I suspect it's aftermarket. With 6 6L6s it might get warm.
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Mike Wheeler · From: Delaware, Ohio, USA

Those fans that are original from the manufacturer aren't there to cool the tubes (they don't need cooling), they're there to remove the excess heat so it doesn't damage any other components in the cabinet, including the cabinet itself.
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Stephen Cowell · From: Round Rock, Texas, USA

Tubes can actually fail from lack of ventilation... if you take a Twin Reverb and convert it to Class A a fan might be wise. Most amps have adequate cooling for the tubes as-is... but adding a fan can prolong the life of both tubes and the rest of the components. Downside, of course, is the noise... so you can get a 12v fan and run it from rectified filament voltage to slow it down. Normally the fan would be right on the final tubes... or you can cut a hole in the side and put the fan there (one of the Allman brothers Marshall mods I believe). Aspen Pittman talks about this in his Tube Amp Handbook I believe.
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Ron Whitworth · From: Yuma,Ariz.USA Yeah they say it's a DRY heat !!

Hello;
I always run a small outboard 110V fan blowing across my power tubes of my tube amps.

I have a Mesa Boogie amp that has the fan built into the chassis but on all my older Fender tube amps I always set a little fan behind them blowing inside.

It seems to me, anyway, like my tubes last longer than the guys who don't use a fan.

It makes me feel better anyway about my tube amps!
Ron
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Craig Schwartz · From: McHenry IL

Would a 12 v fan be recomended in a rack system that warms up with a revalation pre with a power amp. I`ve been wondering if that would be a good idea or just overkill ?
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Bill Duncan · From: Lenoir, North Carolina, USA

The reason I had questions about fans installed for tube amps was that my amp is mounted with the tubes down, and the chassis gets quite warm. For a fact heat is a real killer for components other than the tubes, and since heat rises, with my chassis above the tubes in the path of the rising heat, I'm adding fans to my tube amps.

So I asked to find out if other folks thought the same way.

An important item I kept in mind was to use a fan that is both quite air flow wise, and not introduce electrical noise into the system either.
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Tim Marcus · From: San Francisco, CA

Fans are a good idea

Implementing them properly can be tricky
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Steve Lipsey · From: Portland, Oregon, USA

But....don't the tubes work better when not excessively cooled? I did that mod to my Marshall - built a computer cooling fan into the large square plastic side handle, back in the day (I thought I was the first one to think of that!) - and then decided I liked it just fine running hot (it never got extremely hot).
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Stephen Cowell · From: Round Rock, Texas, USA

For final tubes, you can control the heat on them with the bias... it's an idle control. Different tubes (and brands) sound better/worse at different idle settings. Most tubes sound better on the 'warm' side... what you're doing is minimizing crossover distortion, the distortion that happens when the waveform turns off one side and turns on the other... that's why Class A sounds better, there is absolutely no crossover with Class A since both sides conduct 100% of the time.

When a tube's plate gets too hot it can start emitting electrons just like the cathode... this messes with the current flowing from cathode to plate and makes them sound bad. A little more heat and you can see them glowing red... a little more heat and the plate, or the glass (!) can melt. The bias has a lot more to do with the heat on the tube than an external fan does... but a cooling fan would tend to drive the bias current down some, which can be adjusted back up. A good bias adjustment is done after the amp is at operating temperature... when you warm up a tube amp, don't have it in Standby, or it won't get warm at all. Also, electrolytic caps have lower ESR at higher temperatures, so the amp will sound better when it's heated up, to a point... the fan can actually help with this, by moving the heat around.

Marshall amps are built perfectly for tube longevity... the tubes are upright, and vertical, with plenty of space around them. Fender amps are not built with tube longevity in mind... the tubes are inverted, and when the amp is kicked back they're at a funny angle, and the heat flow can be trapped if there's not a decent gap between baffle and chassis.
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John Billings · From: Ohio, USA

About 50 years ago, I put a Pamotor fan in my old Showman.

Eric Philippsen · From: Central Florida USA

The only amps I've ever run across that required a fan (but didn't originally have one) were the earliest Vox AC30's. They were Class A and the chassis was mounted sideways such that heat from the tubes rose up into the cabinet which had no ventilation screens or holes. The result? They got super hot super fast. That's why so many of them blew up and the transformers' wax melted like butter.

But they sure sound good.

Paul Honeycutt · From: Colorado, USA

I have a Mesa Boogie MK I RI that has a fan mounted in the bottom of the cabinet. I can't say I've ever used it. It plugs into the AC outlet on the back of the amp IIRC. I just saw a picture of AC/DC with a stack of Marshall heads with fans mounted on the side. It's probably not a bad idea, but a lot of amps have been carrying on for decades without them.

Greg Cutshaw · From: Corry, PA, USA

We still have induction heaters in my shop powered by vacuum tubes. The smallest one produces 10KW with a pair of 6960A tubes. These tubes are $2250 new and $840 to have them rebuilt. The last one failed intermittently with a control grid to cathode short. Very scary unit when things go bad! The 6960A's are water cooled and the water is cycled through an external heat exchanger or sometimes we just use city water.

John Faulkinbury · From: Topeka, Kansas

When I had my '63 Fender Bassman head, I took the front cover off and had a fan at the back of the amp, not so much for cooling the tubes as it was for keeping the air flowing.

Dave Hopping · From: Aurora, Colorado

My Mesa-Boogie Mark 3 came with a fan,which I always ran.Had 4 big bottles(and a whole lot of little ones)in a cab roughly the size of a blackface Princeton.

The whole topic of chassis cooling brings to mind a Q I've had since forever:The Fender 4-10" Concert amps came from the factory with 2 back panels,the bottom one having openings with grillcloth,and the top one having no openings.It'd seem to me that the panel with openings would give better ventilation and should be on top.Buut nooo!Anybody know why?

Erv Niehaus · From: Litchfield, MN, USA

Quite a few rack mounted amps have fans. Oft times the fans get noisy and become very distracting.

Len Amaral · From: Rehoboth,MA 02769

I agree with Erv. The power amps that I had with fans and racks with fans were distracting. I'm saying it's not a good idea but those little gizmos can be noisy.

Daryl Thisdelle · From: New Brunswick, Canada

I would have to agree with Stephen Cowell on it is more important to bias the tube properly and run it at the right temperature then to have a fan. He stated that a tube must run hot to get the proper sounds from it so cooling a tube with a fan is usually used to just move air around and to not cool tubes. The hotter the bias(the tube runs hotter) the shorter life of the tube. The problem with bias and tubes as soon as you set the bias it is not long after it has changed. I like to run solid state as far as my amp set up. I do not have to worry about warming up or being careful not to hit the cabinet or anything like that. I save my tube gear for in my home recording studio where everything stays in its rack and not is banged around or goes through big temperature changes. I have the Walker SS System and all my problems vanished.
Daryl
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Bill Duncan · From: Lenoir, North Carolina, USA

Rarely is there a perfect answer. The fifty watt tube amp I use doesn't need a fan. It only has two 6l6's and three 12ax7's, and the back is almost fully open, and heat is not a problem.

The hundred watt I have has four 6l6's and three 12ax7's, and has a enclosed speaker with a floor below the tubes about an inch, thus limiting airflow somewhat.

Before the fan it got really hot and that can't be good. I wish I could do without the fan, but I think that would be asking for problems.

I never found a fan meant for computers that I thought was quite enough, the one I finally used came from a vector drive, and it is very quite. It seems to be working as intended and now my amp stays cool.

Even the hundred watt amp would most likely be OK without a fan if I had stayed with the factory cabinet which was an open back. But what fun would that be?

There's always a trade off
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Jim Kennedy · From: Brentwood California, USA

heat and moisture are two of the biggest enemies of any electronic gear. I'm talking about spilling beer spilling beer on your amp on a hot night. I worked on all types of communication equipment from phones to microwave transceivers while in the Navy. Heat and humidity were our two biggest concerns. almost always the solution to both was to get the air moving. For guitar players, it's always a trade off. If you believe your gear is running to hot, install a fan. better safe than sorry.
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