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Horizontal tube placement


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6/6/2000 2:53 PM
Winnie Thomas
Horizontal tube placement
Okay, Here's my newest question:  
 
Can the tubes in a guitar amp be run horizontally, that is, parallel to the floor?  
 
Winnie
 
6/6/2000 3:50 PM
PTJohn

This is secondhand from the kind folks at Antique Electronics, they told me that preamp tubes will work OK in any orientation, but power tubes are going to work best and last longest in this order:  
1 - base on the bottom, vertical  
2 - base on the top, vertical  
3 - horizontal  
 
The reason for this is the mass of the components inside the tube. It kinda makes sense, with the heat and the large plates and such.  
 
Hope this helps.  
John.
 
6/6/2000 4:36 PM
Ray Ivers

Winnie,  
 
I think the major issues are 'grid sag' (grid misalignment over time due to gravity; the main reason why tubes are not supposed to be stored horizontally), cooling, and physically keeping the tubes in their sockets under shock loads. The grid sag issue should less important with beam-power tubes, and more important with 3-grid power pentodes like the EL34 / EL84. GEC was quite specific about KT88 horizontal mounting ("pins 4 and 8 of each tube are in the same vertical line"), i.e. plate-structure 'holes' if any top and bottom, plate-structure 'wings' (main heat-dissipation area) left and right.  
 
Steve at VHT told me that to date they have had no VHT rack-mount power amp tube failures directly attributable to horizontal mounting, but these are fan-cooled amps. I personally would not recommend this type of tube mounting, for reliability reasons, but I really haven't too much experience with it so don't necessarily take my word for it.  
 
Ray
 
6/6/2000 5:00 PM
Peter S

When I was in the design stages of the Kimerik 50 watt amplifier I did quite a bit of research on this subject. I built protypes with horizontal and vertical orientation. I ended up choosing the horizontal orientation because my amps have a lifetime warranty on them and I wanted to get the best possible reliability from them. As long as you use correct pin orientation when mounting power tubes horizontally there will be no adverse effect on tube life. What the prototypes taught me was that in a properly designed cabinet, the horizontal tubes run MUCH COOLER, due to convection currents set up by the tubes heating of the air around them. This results in a very cool running chassis and tubes that run about 40% cooler than vertically mounted tubes. The same effect could be achieved using a fan only convection cooling has no moving parts, no noise and dosent use power. So far, 14 years later, it is apparent that tube life is not adversely affected by mounting the tubes this way, and may even increase tube life as long as you meet two important Caveats.  
1) Correct pin orientation......the correct pin orientation for horizontal mounting of power tubes can be found on the tube data sheet.  
2)proper venting of the cabinet with a vent above and below the tubes to allow convection currents to flow past the tubes and exit the cabinet.  
 
Peter S  
Kimerik Amplifiers
 
6/7/2000 2:00 AM
Ray Ivers

Peter,  
 
It was good to read your post about operating tubes horizontally. I've always been so religious about storing tubes vertically, and I figured that if there were problems with having them horizontal when cold, imagine what must go on when they're HOT! But with your experience and the VHT amps I've seen, I'm going to revise my judgement - which is great, since I've always wanted to use horizontal tubes for compactness. I can also see how they would run cooler, since the heat immediately 'leaves the scene' rather than traveling up along the envelope to heat up the top (or base) of the tube. The VHT's use vents above and below the tubes, and they run nice and cool. I think I would want to use tube retainers, but they are a good idea anyway.  
 
Ray
 
6/7/2000 3:18 AM
Peter S

Ray,  
Tube retainers are pretty much an absolute neccessity. Some of my early prototypes didnt have them and I had many a tube with a broken off locator pins. Spring and hats work best, but I have an amp I'm using now with Fender style clip retainers, and it seems to work just fine. The convection cooling that results from the horizontal mounting is pretty amazing. The chassis never even gets vaguely warm. It keeps the electrolytics nice and cool too. The compactness is also a great benefit. Dont forget the vents above and below or you lose most of the benefit of the convection. I imagine that if you didnt have good ventilation, you would get a distortion of the geometry of the tube and probably have problems with premature failure.  
 
Peter S  
Kimerik Amplifiers
 
6/7/2000 2:15 AM
Winnie Thomas

1) Correct pin orientation......the correct pin  
orientation for horizontal mounting of power tubes  
can be found on the tube data sheet.  
2)proper venting of the cabinet with a vent above  
and below the tubes to allow convection currents to  
flow past the tubes and exit the cabinet.  
 
 
Peter, I remember seeing this somewhere, but can't recall. I checked out several tube pages but couldn't find the pin orientation. I'm interested in 12A_7, EL84, 6L6, 6V6 and rectifier tubes 6CA4, 5U4 and 5AR4.  
 
This has been very helpful, thanks.  
 
Winnie
 

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