Time for another tube question. First of all, thanks to the folks who post good information on this site. I know the sharing of information freely can be a pain but it's the backbone of Audiogon in my opinion. You all help to keep my tube equipment in good health and that makes me happy.
Ok, down to business. I am running the following setup in a home made rack.
ARC VT-60 and a Mark Levinson ML 27.5 on the bottom shelf the amps have about 6" of vertical clearance to breathe before the next shelf.
The next shelf has a Levinson 360S DAC and a No 37 Transport side by side and they have about 2 inches of vertical clearance to breathe.
The next shelf holds my Modwright SWL 9.0 Linestage and my Dynalab Tuner side by side they have about 3" of vertical clearance.
The amps get hot ... especially when I add ale on a Friday night. Too hot? I'm not sure ... but hot enough for me to put a small desk fan behind them to keep the air flowing. The fan works well but my question is :
How does this affect the amplifier? Tube amplifiers are designed to get hot ... that's the idea ... right? At what point do I risk negative impact on sound quality? Do I even want to go down this road? I see that ARC has put fans in the VT-100 so I don’t think I'm too far off base. I don’t like the fan noise so I am having fan mounts built and I am going to use 12 volt 120mm ultra silent PC fans. A little less air flow but very, very quiet. They will be easily replaceable and will only cost about $7-12. I figure I will get a couple years out of a set. I'll run one across the pre and one across the amps.
The heat will not likely have a negative affect on the sound, UNTIL one of the parts gets cooked by the heat. Using forced air cooling should add life to the units and extend tube life, as well. Have you checked to see how hot the bottom of the DAC and Transport get? There could be a lot of heat radiated from the shelf over the amps.
I had thought that cooling tubes with a fan produced uneven temperatures on the glass envelope and was not a recommended procedure, as this practice would actually shorten tube life as a result. Knowledgable people please chime in on this.
McFarland (and Horseface), There is no harm in placing a small fan behind a tube amp and draw air accross the entire amp. I think the no-no is putting a fan in front of the tubes themselves and forcing air on the tubes.
Tube amps need no fan assistance unprovided by the manufacturer if you are running it in an open area with sufficient ventilation under, over and on the sides of the amp. If you need to enclose an amp, simply measure the temp in the enclosure close to the top of the amp. So long it is within normal temp ranges for your personal living it shouldn't be a problem for your amp.
Unfortunately, in this situation, Horseface has a SS amp which generates some heat and interferes to some degree with the ventilation under the tube amp (I'm not sure how hot the Levinson gets but its a heavy duty amp and the competitors models I've owned there was a fair amount of heat to the touch. He has 6 inches clearance above the top of the tube amp. Under normal circumstances I would think that would be, marginal but adequate (he could check the temp at amp level and see how much hotter the air was there to be sure. But IMHO, his piling up the two amps has the potential to overheat both amps. I think his solution by placing small fan(s) behind the amps drawing air away from them is an excellent idea. It might be overkill, it might not, but there is no down side if he can control the fan noise.
At least that is my experience with tubes and fan YMMV.
My Shanling tube monos are on the bottom shelf of my 5-shelf rack. Their ceiling is the next shelf up, about 2 inches from the tops of the output tubes. That was too close for me so I removed the second shelf. The amps now have 10 inches of clearance overhead and they stay a lot cooler. It's a pain to lose the shelf, though.
To clarify the Levinson and ARC are also side by side with 2-3 inches on both sides and I only run one at a time. I did run them both for a while in a bi-amp arrangement ... I was very pleased but not to the point of running that setup permanently. I like to run the Levinson in the summer as the ARC heats up the whole room. As for the VT-60; I have the cover on the amp so the air blowing across the unit pulls heat transferred to the chassis cover not the tubes directly... in that regard, I guess the cover acts as a heat buffer. The DAC was getting warm which was how this all got started. When the 360S gets too warm it gets very grumpy. I checked it with the desk fan on and it's just a bit warmer than normal. It's all running fine now. I have just completed a test with and without the fan. I cant hear much if any difference in sound. The fan project is a go. I am going to avoid the fan directly blowing across the tubes and I am considering pulling air vs pushing.
I'm stuck in this little 14' X 15' bedroom until I build the addition to my home. I am really intersted in a pair of Cary or McIntosh tube amps but in this room I think I might cook myself. I want to pull the amps out and set them up close to the speakers on amp stands with lots of room to breathe. Until then ... the VT-60 is as far as I want to push it.
When you are 'drawing' the heat away from the tubes using induced draft, what air do you think that the tubes air are getting to remove the heat? The same cold air as if you had the air 'blowing' directly on the tubes as in forced draft. It doesn't matter how the air is circulated over the tubes, induced or direct. With sufficient overhead space AND surrounding space, natural convection is sufficient, i.e. don't put power amps in cabinets or in tight shelves without fan-cooling or leave them out in the open.
Honestly, the easiest solution is to pull your amp out of the rack. Find it a better home or on an amp stand. Pre-amp and gain tubes produce very little heat by themselves. The amps will cook everything above it.
I would never use a fan. 1-it would have to be plugged into a seperate circuit to avoid noise. 2-you very easily can get added noise by the "breeze" blowing over the tubes. 3-even if the fan draws air away, you will end up with filthy equipment.
interesting thread! i made a layered posterboard and cork spaced 'breathing' elevating shelf for my dvd which i set atop my sony ht receiver to keep heat off dvd. cut out cork corner squares 2"X 2" and glued them to corrugated poster board (3 levels) cut to fit dvdp feet. stopped amp heat from reaching dvdp and still allowed amp to cool. i think the concern about the heat from lower amp heating amp above is valid. insulating the shelf from heat transfer is simple way to fix. you don't need much circulation for tubes heat imo but you do not want them heating other gear obviously. i like pc fan idea :)
My father built a Dynaco Stereo 70 amplifier in the 1960's. He plugged a fan into the switched outlet of his home-made Dynaco preamp, and has had air blowing directly onto the power tubes for about 40 years. I'm telling you, he played a lot of records during those years, and plays a lot of CDs now, turning his system on almost every night. Well, those original Mullard EL-34 tubes (with Dynaco labels) are still working fine, test like new in my tube tester, and will not need to be replaced as long as he lives. Now a little more detail: he never used the amp cover, has his amp located under the cabinet that houses records and equipment, has the bottom shelf of the cabinet just about 1 inch above the top of the power tubes , and the cabinet has front and back decorative skirts that further enclose the amp in a very confined area. So I think his intention was to protect his wood cabinet from catching fire as much as it was to extend tube life. I think he accomplished both.