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Mr. Triatic 6th August 2004 11:07 AM

mounting tubes upside-down
 
hi!
i wonder if there´s some problems with mounting a tube upside-down? the tube is a PCL86, i know that some tubes life is dependant on how they're rotated when mounted horizontal for example 829 or 832, but if they are vertical but upside-down?

SY 6th August 2004 11:20 AM

Turning the tubes upside down will cause all the electrons to fall out. You'll have a real mess on the floor. You'll have to get out your molecular tweezers to get some of those electrons out of the carpet.

As for the real answer, it seems to be no problem. I've got and amp in-house using 6550 outputs upside down and had zero problems with tube life. Haven't done it with a PCL86, but that's got a structure which looks symmetric. The one caution would be to ensure that air flow around the tube is not impeded by the chassis- warmed air rises.

jane 6th August 2004 11:47 AM

Re: mounting tubes upside-down
 
Quote:

Originally posted by Mr. Triatic
hi!
i wonder if there´s some problems with mounting a tube upside-down?

No I don't think so.
Remember that many of the old guitar amps had the tubes upside down...

fdegrove 7th August 2004 12:11 AM

Hi,

Quote:

Remember that many of the old guitar amps had the tubes upside down...
............And used retainer clips to keep'em seated.

IMHO, it not such a great idea to have tubes mounted tip facing downwards.
Unless there's no other way I just wouldn't do it. It's just plain asking for trouble.
Current production sockets are nowhere near as tight a fit as they should be for this kind of operation, especially not those dreaded Chinese clo(w)nes...
Besides, how are you going to replace them? By dismantling half of the amp while you could have just pulled them out from atop?

Cheers, ;)

rcavictim 7th August 2004 12:53 AM

Speaking of those tube amps like Fenders, etc. that all mounted the tubes hanging downwards, I think this is an especially bad idea because heat naturally rises and this bakes the snot out of the chassis components, or in the case of newer amps bakes the circuit boards causing heat related failures also in solder connections and traces.

One case where mounting the tubes upside down is in tube amps manufactured in China and exported to North America. Once on our shores the tubes are all right side up! :D

Some directly heated tubes including the 5U4, 5Y3 type rectifiers as well as power triodes must be mounted either vertically, or with special attention given to pin orientation if Horizontal so that filament sag will not cause an internal short. If a tube can be mounted sideways, or upside down the good tube manuals say so, and say how.

The english language is weird. "Upside down" could be interpreted to mean that there is an upside to mounting it pointing down no? :xeye:

Positron 7th August 2004 10:55 PM

Tube pins
 
I think RCA alluded to heat rising, solder connections etc. Another sinister problem is the heat around the tube base, the pins.

Heat is transferred through these pins, especially the filament pins. I prefer to keep the tube upright so the cool air surrounds the tube socket, helping to cool the socket and therefore pins.

Otherwise, harder to keep the tube pins cool.

Hope this helps.
Steve

Richard C 7th August 2004 11:25 PM

Re: mounting tubes upside-down
 
Quote:

Originally posted by Mr. Triatic
hi!
i wonder if there´s some problems with mounting a tube upside-down?

Absolutely, this should only be attempted when either seated or standing, anything else is just plain showing off and could easily result in injury.

v-man 8th August 2004 12:14 AM

the only reason a lot of guitar amps use their tubes upside down is because its easier and cheaper to make the chassis,and keep all the controls at the top of the amp, eg, messa boogies, marshalls etc,[i have them in for repair all the time] it is not a paticularly good idea to run any output tube upside down, some of the more serious reasons being, they cook the tube bases and cause hairline fractures,which lead to high voltage shorting, as other people have allready stated, they cook the hell out of the components on the top of the chassis,especially the power supply electrolytics. in some circumstances,in the case of octal based valves, eg, EL34, 6L6, KT88 6550, etc, i have known the solder to melt on the tubes bases!!!also, if they use printed circuit boards, [as most of the new amps do] the heat warps the printed circuit boards, again leading to cracks, and track failier. there are more reasons but i think you get the picture by now,if you want convenience, then go ahead,but if you want long term reliability, put some thought into the design, and do it right. ;)

RE 604 8th August 2004 12:18 AM

Hi to all ,
take a look at the german studioamps like V 72 , V 73 , V 76 , V 81 and so on . The tubes in this legendary amps are mounted horizontal and upside down in extremly small cases and they worked for years and years without problems .
Many of my amps are older than 50 years and I only changed the electrolytics in the power supplies .
Regards , AlexK.

fdegrove 8th August 2004 01:10 AM

Hi,

Quote:

take a look at the german studioamps like V 72 , V 73 , V 76 , V 81 and so on . The tubes in this legendary amps are mounted horizontal and upside down in extremly small cases and they worked for years and years without problems .
O.K...but those are mic preamps running at low currents and mostly horizontally mounted tubes, alligned in such a way as to avoid microphony at all cost.
All little engineering masterpieces, I must add.

The PCL86 however is a little powerhouse that's good for about 12W of plate dissipation alone....

Besides, what's to be gained in the case of upside down mounted powertubes for domestic use?

Cheers, ;)


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