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Valve orientation?

 
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Valve orientation?

Post by Katie Bush » Mon Aug 24, 2015 8:23 pm

I suspect this question has been asked before, but couldn't be certain.

Anyway, here goes.. Is there an ideal orientation for the optimum operation of the thermionic valve? It seems that for many years, valves were orientated vertically, and almost universally.. One could remove the back cover from a radio, TV, record player or amplifier, and the valves were almost always standing vertically - perhaps they were too large and heavy to be orientated in any other way?

In later years, it was extremely common to find the chassis was now vertical, and the valves were orientated horizontally - maybe it was just because smaller and lighter valves were less physically problematic in this orientation than their older and larger cousins? :aaq

However, given that electrons have mass, it would seem logical to arrange the valves vertically? Surely, horizontally mounted valves would tend to emit a greater quantity of electrons in the vertically downward direction than the upward direction? If so, valves mounted horizontally would exhibit some degree of bias in the direction of electron flow? The same would not be true in the case of vertically mounted valves.

Going further, there were numerous TV sets whose chassis were constructed with diagonally sloped top surface, and the valves mounted at a rather jaunty angle.

So which orientation would be best? Presumably there was no significant difference, otherwise the set makers would have factored that into their designs, but from the "perfect world" perspective surely there would have been an ideal orientation? :aab

Marion

 
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Re: Valve orientation?

Post by Ed Dinning » Mon Aug 24, 2015 8:33 pm

Hi Marion, as far as I know it is discouraged to mount valves vertically down as this leads to increased heating of the base/ pins.
Mounted horizontally, the pins supporting the internal electrodes should be vertical to prevent sagging grid wires and poissible internal shorts.


Ed

 
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Re: Valve orientation?

Post by Valvebloke » Tue Aug 25, 2015 12:38 am

Katie Bush wrote:... However, given that electrons have mass, it would seem logical to arrange the valves vertically? Surely, horizontally mounted valves would tend to emit a greater quantity of electrons in the vertically downward direction than the upward direction? If so, valves mounted horizontally would exhibit some degree of bias in the direction of electron flow? The same would not be true in the case of vertically mounted valves ...


The electron mass is really, really small so the effects on them of the earth's gravitational field are completely negligible compared with those due to the electric fields in a valve, or even those associated with the quasi-thermal process of thermionic emission. In almost all real-world cases the same is true even of single atoms, which are typically tens of thousands of times heavier than electrons. But the people who make ultra-precise atomic clocks have managed to make use of the gravitational pull on atoms in the so-called 'atomic fountain' https://en.wikipedia.org/wiki/Atomic_fountain. In this the atoms are 'fired' very gently upwards and then brought to a standstill by gravity acting downwards (of course :bba ). This allows their transition frequency to be measured very, very precisely indeed.

VB

 
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Re: Valve orientation?

Post by Refugee » Tue Aug 25, 2015 2:28 am

I am pretty sure it is mostly down to the mechanical construction of the electrodes.
Early pinch construction valves were a bit more fussy about orientation but later types were a bit more robust and the data sheets often stated that they could be used in any orientation.
The effect of gravity on electrons is very small and can only be measured with extreme test equipment.
I like the blanket stitch on the atomic fountain in the Wiki article :aad

 
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Re: Valve orientation?

Post by ntscuser » Tue Aug 25, 2015 2:46 am

Katie Bush wrote:In later years, it was extremely common to find the chassis was now vertical, and the valves were orientated horizontally - maybe it was just because smaller and lighter valves were less physically problematic in this orientation than their older and larger cousins? :aaq


Surely it had to do with the introduction of printed circuit boards in place of hand-wired chassis?

 
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Re: Valve orientation?

Post by mark pirate » Tue Aug 25, 2015 3:57 am

as far as I know it is discouraged to mount valves vertically down as this leads to increased heating of the base/ pins.

I have a Marconi radio where the valves are mounted upside down! I have also seen guitar amps that do the same.
On the Marconi set there are no clips to hold them in place :aaq

 
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Re: Valve orientation?

Post by turretslug » Tue Aug 25, 2015 10:57 am

It suits things like combo amps to have the bottles fitted upside down, with chassis-mounted controls at the top and speaker underneath- I agree that it's not ideal but perhaps it's expected that valves get a bit of a caning anyway in this circumstance so any life-shortening is lost in the stats. I was once brought one of these with the comment "It's distorting a bit when I turn it up". I resisted the urge to quip, isn't that the reason for its existence, and it was quickly obvious that one of the push-pull modern EL34-alikes had dropped out of its unrestrained socket. Nice easy fix.... I wouldn't be surprised if the excess heat transfer to the base had made the contacts lose their springiness, though.

 
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Re: Valve orientation?

Post by Briancuff » Tue Aug 25, 2015 12:55 pm

Pye produced a series of broadcast quality monitors, the 2780/2788s in in the early 1950s in which the chassis was vertical, similar in design to the PTV domestic TV (but not so accessible) so it's not that new!

 
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Re: Valve orientation?

Post by Kalee20 » Tue Aug 25, 2015 10:50 pm

The Tektronix 545a 'scope has many valves mounted base-up... But it does have a big cooling fan.

Tuning indicators of the EM80 type seem to be as likely mounted base-up as base-down, behind their escutcheon.

 
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Re: Valve orientation?

Post by Terrykc » Wed Aug 26, 2015 11:31 pm

Katie Bush wrote:... In later years, it was extremely common to find the chassis was now vertical, and the valves were orientated horizontally - maybe it was just because smaller and lighter valves were less physically problematic in this orientation than their older and larger cousins?

Marion, I'm afraid you are missing the blindingly obvious here!

Early sets had narrow deflection CRTs which took up a lot of space, so the horizontal chassis could occupy the space underneath it (and usually did).

Fast forward to the 110° slim-line tube and the desire of the marketing department to accentuate the feature by making the cabinnet even shorter than it really ought to have been and all that horizontal space vanished. By now, of course, increased screen sizes meant that the amount of vertical space had increased in the interim so a vertical chassis was the perfect choice!

This had already started to happen with the earlier 90° tubes, of course.

Later solutions were the two tier arrangements loved by Thorn and the box formation favoured by Bush but the large horizontal chassis was gone for ever ...

 
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Re: Valve orientation?

Post by Katie Bush » Fri Aug 28, 2015 9:37 pm

Hi Terry,

You're too telly orientated! Radios don't have CRTs, nor record players, but a lot of radio, even if not so many record players, still went for vertical chassis.

In any case, my question was framed in the "perfect world" (for the valve) scenario, rather than what was practical for the set makers.

Marion

 
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Re: Valve orientation?

Post by Terrykc » Fri Aug 28, 2015 10:27 pm

Sorry Marion,

I wasn't considering perfection - or anything like it! - just practicalities ...

As far as radios are concerned, the vertical chassis probably became more common after it was adopted for TV use but was also used in earlier sets where space was at a premium - the Bush MB60 springs to mind here.

As for record players, restricted and awkward spaces meant that manufacturers squeezed the electronics in any which way they could!

Ventilation problems excepted, I don't recall any reliability problems caused by the valves being mounted horizontally ...

 
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Re: Valve orientation?

Post by mark pirate » Sat Aug 29, 2015 8:37 am

the Bush MB60 springs to mind here

Several later Bush sets had vertical chassis, the DAC70/VHF90A and VHF80 are among them.

 
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Re: Valve orientation?

Post by Doz » Sun Aug 30, 2015 12:30 pm

Check the 5U4 rectifier data sheet here http://www.r-type.org/pdfs/5u4gb.pdf

It states it must be vertical, unless pins one and four are in a vertical plane, presumably to stop the filament sagging.

 
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Re: Valve orientation?

Post by Russell W. Barnes » Wed Sep 02, 2015 11:19 am

The Marconi B6122 HF transmitters were designed with the first audio stage - a Leak amplifier - mounted so the valves were horizontal. The BD272 transmitter, of a similar design, had the Leak amplifiers mounted with the valves vertical. There was no difference in valve failure rate whatsoever, and bear in mind these amplifiers were running nearly 24/7.

I might add that the early Band II translator relay sites had horizontally mounted valves too, as did the drives in the Band I TV transmitter input equipment bays. We're talking B7G / B9A valves here (apart from the rectifier valves in the Leaks).


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