Tube direction and head design.

[Outlaws]

So I just yanked the chasis out of my ProJunior. Its time to make a head so I don't keep thinking I just pissed off a rattlesnake.

Problem:
The chasis was designed for the controls on top and the tubes facing down.
(see pictures below)

Now I am really not interested in having a head with the controls on top and the tubes staying where they are. The thingwould be at least 10" tall. Thats a big head IMO considering the chasis is only 13.5" accross the front.

So I am thinking that if I make it around what is already there, and I use a thin sheet of metal for the back plate rather than what thick bottom would need, I can make it 9" deep instead of needing 10". And depth won't look as dumb as being tall.


Now the question:
Is there any problem with having the tubes horizontal?
I can't seem to see why they would need to be in a verticle manner for any reason if upsidedown and rightsideup don't matter.

I also realize that the tubes would be close to the bottom, so I would probably mount the chasis on a 1" piece of wood first.


Any thoughts on this?

Also any suggestions for a better way to make this head container?
Eventually I would make a matching cab for a 12".

 

[AlfredB]

bear in mind i am no expert ....


but i dont see any reason for probs w/ tubes horizontally ... there were many amps made that could be reclined, etc... (resulting in similar tube-positions)

also the very fact that you make a head, thus getting the tubes out of the rattle-environment of a combo should help also (tubes NOT ratteling loose) ...

so - just go ahead!

 

[Le Basseur]

And depth won't look as dumb as being tall.

I know at least 5 dozens of Marshall guys that'll kill you for these words!!!
Seriously,leave your amp as is.The combo cabinet is pretty well done so why bother with two boxes instead a single one?!?
Regarding your question:
Modern tubes are not at all picky about their position,being horizontal or vertical.This is because the tubes are INDIRECTLY heated,as opposed to directly-heated tubes used in VERY old amps or in modern high-end,but that's another story.
Anyway,a modern tube may stay vertically (pointing upwards like in Marshalls,Sunns,etc or downwards,like a bat,as in Fenders,etc.).Also,the horizontal position is permitted BUT after two decades of amp repairing,I wouldn't reccomend that.Why? Because in a horizontal mount the glass' temperature is very different below (colder) from the beneath (hotter).This is a normal issue:think about how the cold air flows from bottom to the top and you'll understand it.I found out that this way of mounting shortens,sometimes significantly,the life of tube for a stupid reason (temperature difference of the glass bulb).Most often,the glass breaks prematurely.
HTH,

 

[boingoman]

I know at least 5 dozens of Marshall guys that'll kill you for these words!!!
Seriously,leave your amp as is.The combo cabinet is pretty well done so why bother with two boxes instead a single one?!?
Regarding your question:
Modern tubes are not at all picky about their position,being horizontal or vertical.This is because the tubes are INDIRECTLY heated,as opposed to directly-heated tubes used in VERY old amps or in modern high-end,but that's another story.
Anyway,a modern tube may stay vertically (pointing upwards like in Marshalls,Sunns,etc or downwards,like a bat,as in Fenders,etc.).Also,the horizontal position is permitted BUT after two decades of amp repairing,I wouldn't reccomend that.Why? Because in a horizontal mount the glass' temperature is very different below (colder) from the beneath (hotter).This is a normal issue:think about how the cold air flows from bottom to the top and you'll understand it.I found out that this way of mounting shortens,sometimes significantly,the life of tube for a stupid reason (temperature difference of the glass bulb).Most often,the glass breaks prematurely.
HTH,

I disagree, except with the comment to outlaws of "Don't do it!"

People mount tubes horizontally in preamps all the time. Many vintage amplifiers (not guitar) also have horizontally mounted tubes. All that is needed is some kind of retainer, like amps with hanging tubes use.

If your logic were true, a tube in any orientation would be in danger, as would light bulbs and headlights in cars.

I don't doubt tubes can break easier when mounted horizontally, but it's from impact shock, moving the amp while the tubes are hot. The elements are very delicate when hot. Also, power tube elements can get hot enough to sag, make contact, and short out.

Power tubes mounted horizontally usually have a specified orientation for this very reason- to prevent grid sag. This is the biggest reason to not do it, outlaws- it's doubtful the tubes are oriented correctly.

Horizontal orientation is actually recommended in some applications, as the horizontal heat dispersion characteristics are better than in vertical orientations.

 

[Le Basseur]

People mount tubes horizontally in preamps all the time. Many vintage amplifiers (not guitar) also have horizontally mounted tubes. .

Yes.You're right.PREAMP tubes.Wich don't get very hot.
What about output tube's temperature?
Did you ever measured a glass envelope's temperature,say,of a pair of 6550's running in AB2 class with PLENTY signal on the input?

I don't doubt tubes can break easier when mounted horizontally, but it's from impact shock, moving the amp while the tubes are hot. The elements are very delicate when hot. Also, power tube elements can get hot enough to sag, make contact, and short out.

Those "elements" wich are prone to sag (bend) when the tube is hot have names... .In fact,the only issue with shorting "elements" appears in a direcly-heated triode where,if wrongly positioned,the hot filament bends and shorts with the grid.
This phaenomena doesn't happen,though,in an indirectly-heated tube,being triode,pentode or whatever.

Horizontal orientation is actually recommended in some applications, as the horizontal heat dispersion characteristics are better than in vertical orientations.

What are the "recommended applications" you talk about?
Are we talking audio here,or general theory?
And where you get from the horizontal heat dispersion thing?
Please define!
Once again:did you ever measured the temperatures of a horizontal mounted tube's glass,both underneath and beneath?Because I did that with a lab probe thermomether for alot of output tube types and the results are far from being even close.This is why I said what I said,not because I read some mumbo-jumbo posted somewhere on a fancy website.
REgards,

 

[boingoman]

Yes.You're right.PREAMP tubes.Wich don't get very hot.
What about output tube's temperature?
Did you ever measured a glass envelope's temperature,say,of a pair of 6550's running in AB2 class with PLENTY signal on the input?

No, I haven't. I don't have to. They get hot. Can you explain why light bulbs don't spontaneously blow up when mounted horizontally? Light bulb filaments run much hotter than most power tubes, and bulbs use much thinner glass. You'd think a light bulb would therefore be more susceptible to what you describe.

Or why some tube amps use cooling fans? By your logic, a cooling fan blowing on tubes will shorten tube life, as it would cool one side of the tubes faster. I'm fairly sure amp makers put fans on their amps to lengthen, not shorten, tube life.

I can think of at least two RF amps that mounted their power tubes horizontally.

Those "elements" wich are prone to sag (bend) when the tube is hot have names... .

No need to get snide. I just didn't think it was necessary to name them.

.In fact,the only issue with shorting "elements" appears in a direcly-heated triode where,if wrongly positioned,the hot filament bends and shorts with the grid.
This phaenomena doesn't happen,though,in an indirectly-heated tube,being triode,pentode or whatever.

The grid can sag as well, if not oriented correctly. Believe it, or don't. The response of the tube can change as well, as the grid sags out of position.

In any case, everything in the tube gets more fragile as the tube heats up. Hot tubes are very susceptible to shock damage. This seems like it would be the more common failure modality in a guitar amp with horizontally mounted tubes.

Also, if tube life is reduced by horizontal mounting, perhaps you could explain why specific instructions are given by the manufacturer for horizontal mounting of many tubes?

What are the "recommended applications" you talk about?
Are we talking audio here,or general theory?
And where you get from the horizontal heat dispersion thing?
Please define!,

Uhhhh....some sweep tubes in televisions, for one. They get really hot in two specific spots. Orienting them vertically means the hot spots are right on top of each other. The tube is mounted horizontally, hot spots down.
A horizontally mounted tube presents more surface area to the cooler air underneath, being convected by the heat of the tube.

Once again:did you ever measured the temperatures of a horizontal mounted tube's glass,both underneath and beneath?Because I did that with a lab probe thermomether for alot of output tube types and the results are far from being even close.This is why I said what I said,not because I read some mumbo-jumbo posted somewhere on a fancy website.
REgards,

Just because you measured a temperature difference doesn't mean it has any effect on tube life. That's a pretty good piece of mumbo jumbo itself.

 

[Outlaws]

Okay you two. Before we bust out the guns or worse yet, get off topic, the power tubes are EL84. Not the biggest tubes in the world by a long shot, but since they are in the power stage they probably are still susceptible to power stage heat.

Anyways, a head will be made in some form or another. The damn thing rattles inside the cabinet and that is unexceptable. Period.

So if I have to go top-down then I guess thats the way it goes. But I am still curious about the real reason for not angling it.

What is this sag you speak of. The only sag I am famialiar with is on my SuperReverb (which also tilts to a VERY nice / position lol) where my recifier can't recify fast enough and I get a the perfect rhythm compressor.

 

[boingoman]

Okay you two. Before we bust out the guns or worse yet, get off topic, the power tubes are EL84. Not the biggest tubes in the world by a long shot, but since they are in the power stage they probably are still susceptible to power stage heat.

Anyways, a head will be made in some form or another. The damn thing rattles inside the cabinet and that is unexceptable. Period.

So if I have to go top-down then I guess thats the way it goes. But I am still curious about the real reason for not angling it.

What is this sag you speak of. The only sag I am famialiar with is on my SuperReverb (which also tilts to a VERY nice / position lol) where my recifier can't recify fast enough and I get a the perfect rhythm compressor.

Really, I don't know if it's gonna make a difference. I may be being a bit cautious. Some people have pointed out tilt-back amps, which don't hurt anything. Horizontal might make a difference, it might not.

If you go for it, and it doesn't work out, you could always change it. Just be aware that it might not be good.

It's different than that kind of sag.

Some parts of the tube, be it the filament or grid, get hot enough that they can actually physically sag due to gravity if the tube is mounted horizontally. They can flex far enough to make contact with another part in the tube, causing a short, or affect performance.

Manufacturers recommend that if the tubes are to be mounted horizontally, that they be oriented so the affected parts are least susceptible to this.

Some tubes aren't meant to be horizontal at all, because they cannot be oriented to protect both grid and filament.

My reasons for at least being careful, or not surprised if it doesn't work out:
1) Tube orientation allowing the above mentioned sag.
2) Tubes are fragile when hot. In my opinion, horizontal mounting could make the tubes more susceptible to shock damage. Just be careful. That's more a caution than a reason against doing it.

I do not know about EL84s. The odds that the tubes are oriented the right way to prevent grid sag are pretty slim, but I also don't know how susceptible they are to it, or how hard they have to be driven to cause it.

LB also feels they are more prone to shorter life in this orientation. I do not, at least not for the same reasons, or to any significant degree.

 

[Outlaws]

Points taken.


Right now I am looking for some way to just re-mount the tube sockets, but the ribbon cables fender used are not going to give me much slack at all. It would be pretty straight forward connections for some new wires. I might get a second (smaller) chasis just to hold the tubes. So I can mount them upright. I think it would work out really well. Cuase I can still use the PCB board and sockets. Just a few holes and some wires. More than I was hoping to do, but at least it would be kosher.