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Are cooling fans recommended for tube equipment ?

Thx for the link -- I like the temp-sensitive feature ... my meager solution, of course, was cobbled together in about 20 mins ... next feature would be the temp-activation, but the tube equipment is always high temp ..I suppose I cld put the AC Infinity under the receiver case ... I have no rack/shelf system yet, but when I do, the Infinity wld let me get away with putting the Fisher on the second shelf instead of the top shelf ....
 
I think the fan really helps components like electrolytic capacitors last longer, even though most are specified to work at 85 degrees C, some at 105 C, which is way too hot to touch. It just feels better keeping them cool, if nothing else.
 
Kappclark;
Cooling is more to keep the Transformer and Filter caps in bounds of their operating temps. Tubes are designed to run "HOT". Hence the term (British) "Thermionic Valve". What everyone has gas over is the fact that the radiant heat cranks up the transformer temps, and cap temps causing eventual breakdowns. But if the output tubes are isolated from the transformers and caps by a heatshield or distance, the chances are less. There are Tube receivers that you can cook Steak and eggs on due to locations and design of components. The Sansui 1000A is a Nuke Plant compared to a 400, heat wise.

Hands are a shitty way to monitor temps. You can't tell if hot water is 105*F or 150*F (very warm to scalding). All you know is that it's HOT! Transformers are designed to work with temps as high as 190*F(in short spurts) with the Average normal high end being about 145*F.

The 400 is designed to get somewhat WARM forward of the HEATSHIELD the output tubes sit behind. There is a good reason for the heatshield. It deflects the high heat from the tubes AWAY from the transformers (yes the power trans too) allowing them(trans) to run cooler. The same goes for the CAN CAPS. Although there is heat generated by the transformer (POWER), comparatively it's a hell of a lot less than 4 glowing output tubes. And higher votlages will make more heat. So trimming the wall voltage will shed some heat too, although it won't be apparent at a casual glance. A laser thermometer is ideal for this.

FISHER specified a 15% variance +/- on voltages in the schematic @ 117V. This was due to component tolerances that were looser than a worn girdle at the time. What you need to do is to open the bottom up and find the heaters for V1 thru V7. Hang your meter on the leads, and ramp up the power so that the voltage on the heaters is no more than 6.3V +/- 5%. (5.9V to 6.6V). FISHER DID Starve heaters (more for lower noise than anything else. With the heaters at 6.0 to 6.3v note the wall voltage on the variac/kill-a-watt. Use that as your wall voltage setting for the variac or aim for that with a buck transformer.
 
Thanks for the detailed explanation -- good idea about laser thermometer .. would there be any at all 'downside' to using a cooling fan on the Fisher 400 ?
 
No downside really. I don't run fans at all (except a room fan to move air around in the room and it's usually 6ft or more away from rig). My executive console has an 800c that is enclosed and runs slightly warmer than the 400 ever will and there is NO FAN period. But Bias on all my Fisher's with Fixed bias is set for NMT 75% of max dissipation, which is substantially cooler than Stock biasing. I've never seen temps above 140*F in my 400's or 800c unless they were running flat out full bias and then trans temps were about 150 for the POWER Trans. Output's were about 130 as I remember. These are fairly normal temps for unaltered (read stock!) receivers of that era.

I have a X-101-B and a FM-100B in a custom console cabinet with an open back. Natural convection allows temps to stabilize at 125*F on the FM-100B and 145*F with the X-101-B on the Power Transformer. Output tubes are running 275-290*F depending on outside or in the middle subject to radiant heat. Obviously the side of the transformer facing the tubes is warmer than the other sides. Laser the top and it gives a decent compromise.

Your choice. I've been running tube gear since I was a kid (I'm 65 now), and never had a need to put a fan on them. Hell, a lot of the tube gear we had in the Navy (early 70's) was tubed and most of it didn't have fans. And very little of the tube gear on the Sub I volunteer on, uses fans (except the Radar and Sonar and they're not getting restored and neither is operable).
 
I’d like to run a Sherwood s5000 amp and S2200 tuner in a rack with other SS components. Cassette, receiver, CD.
Rack is in a built in cabinet with wall venting top and bottom. Small computer fans are in the top exhaust vent and they are controlled with thermostatic switch.

I’d like to keep the Sherwoods toward the bottom of the rack with other components above them. Concern is the heat of course, especially the amp.

Any recommendations for spacing of the tube components, are they a must do at the top of the rack with amp on top, or advisable to just keep them out of the enclosed cabinet?

Thanks
 
Unless installed within an enclosed furniture console, the short answer is no. Manufacturers knew what they were doing where it came to designing tube equipment to provide adequate ventilation nor is there any benefit to trying to reduce the surface temperature of the tubes themselves.

Heat tends to draw dust; fans also draw dust. All that will be accomplished is accelerated dust accumulation on, in and around the unit.
 
So keep them out of the cabinet entirely? No spacing is adequate?

The fans do no blow on the components, they aid venting out of a tall "audio cabinet" or "closet" that is enclosed. I can eliminate the exhaust fan venting if that would be preferred for dust accumulation.
 
MtnAudio said:
So keep them out of the cabinet entirely? No spacing is adequate?

The fans do no blow on the components, they aid venting out of a tall "audio cabinet" or "closet" that is enclosed. I can eliminate the exhaust fan venting if that would be preferred for dust accumulation.
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Auxiliary cooling is not necessary with OEM accessory cabinets (assuming the factory's clearance recommendations followed). Only when the component is built in to custom made furniture as was common in the '60s where heat could build up rapidly is when fans are called for. For equipment sitting on a tabletop with plenty of free space above (or around 6" or so) clearance above the unit, there should be no need for any special measures.

Correct, the air flow should never be directed toward the unit but a fan placed behind the unit blowing rearward will still draw dust from the front. AK member here once tried that with a McIntosh tube amp (fan at rear and blowing rearward) and said all he got was a mess and never did it again. When built into an enclosure, dust is less likely since the rest of the cabinet is more or less sealed.
 
So am I wrong in adjust bias for this? I've definitely cooled off my bulbs. Was careful in not adjusting too much as to over heat output transformers... solved my problems I believe... atleast thousand hours on it. Tends to take longer to warm up to operational temp....
 
62caddy said:
Auxiliary cooling is not necessary with OEM accessory cabinets (assuming the factory's clearance recommendations followed). Only when the component is built in to custom made furniture as was common in the '60s where heat could build up rapidly is when fans are called for. For equipment sitting on a tabletop with plenty of free space above (or around 6" or so) clearance above the unit, there should be no need for any special measures.

Correct, the air flow should never be directed toward the unit but a fan placed behind the unit blowing rearward will still draw dust from the front. AK member here once tried that with a McIntosh tube amp (fan at rear and blowing rearward) and said all he got was a mess and never did it again. When built into an enclosure, dust is less likely since the rest of the cabinet is more or less sealed.
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Your so right. Hard enough keeping your gear from getting dusted. Reminds me of a curling iron smell haha. Cover it when not using it. Hood off while I am. But hey im new at this. I suspect I just take hood off for the beauty of it. House is 69 degrees year around. I think maybe that's more important part of it all. No temperature or humidity change. Extra emphasis on the humidity.
 
62caddy said:
Auxiliary cooling is not necessary with OEM accessory cabinets (assuming the factory's clearance recommendations followed). Only when the component is built in to custom made furniture as was common in the '60s where heat could build up rapidly is when fans are called for. For equipment sitting on a tabletop with plenty of free space above (or around 6" or so) clearance above the unit, there should be no need for any special measures.

Correct, the air flow should never be directed toward the unit but a fan placed behind the unit blowing rearward will still draw dust from the front. AK member here once tried that with a McIntosh tube amp (fan at rear and blowing rearward) and said all he got was a mess and never did it again. When built into an enclosure, dust is less likely since the rest of the cabinet is more or less sealed.
Click to expand...
I'd also say tube shields as an option if was that big a problem.
 
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