Why 6.3V?

[Radio_Dave]

Just what is it about 6.3V (and for that matter 63V and 630V)?

It seems like such an odd number, yet is it a 'standard' voltage for valve heaters, bulbs and capacitors, etc.

David

[jjl]

I believe that 6.3V was chosen as a standard for valve heaters as it is close to the voltage obtained from a 6V automotive lead acid battery when fully charged. 63V and 630V I'm not so sure about.

John

[Jonster]

That would sound plausible as a 12V lead acid battery gives nominally 12.6V.

[FRANK.C]

That's a good question Dave and is something that I wondered about myself. The same goes for fuses with 6.3A and 3.15A which seam unusual values.

Frank

[John M0GLN]

There's been a previous thread about this and I posted this link about Renard's Series.

http://www.sizes.com/numbers/preferred_numbers.htm

I don't know much about it, its just a site I found that explains all these odd numbers.

John

[Radio_Dave]

Oh well it looks like John has the answer. 6.3 is part of a geometrical series of preferred numbers .

It's a pity because I really liked the 6V lead acid battery idea

Regards
David

[mickjjo]

The first 6.3 volt 0.3 amp "Tubes" appeared in 1931, types 236, 237 & 238, and were designed for running from a 6 volt car battery :-

http://books.google.co.uk/books?id=X...page&q=&f=true

Regards, Mick.

[John M0GLN]

Originally Posted by Radio_Dave

Oh well it looks like John has the answer. 6.3 is part of a geometrical series of preferred numbers .

It's a pity because I really liked the 6V lead acid battery idea

Regards
David

I suppose if it had been chosen to suit the lead acid battery, then the first 2V valves should have been 2.1V, but there's still some to explain, two for example, DF64 at 0.62V and a DF66 at 0.625V, you wouldn't think that a difference of 0.005 of a volt would matter, or even been achievable.

John

[KeithsTV]

Many early sets had a rheostat in series with the filaments so presumably the voltage from a fully charged accumulator could be adjusted down to 2v for the filaments.

I had always understood that the 6.3v was derived from the fully charged 6v battery idea. Perhaps its coincidence that it matches the preferred numbers.

Keith

[wireful3]

Like Keith I also thought it was based on using a 6v lead acid battery for valve heaters and assumed that the ISO value was coincidence. Wikipedia gives the ISO standard as being set in the early 1950s so it seems there is no direct link.

Because the Renard series was known long before valves were used, some intellectually inclined engineer might have thought it a good idea to chose this when looking at the discharge performance of 6v accumulators. It is unlikely but I have come across some bizarre reasons for choosing something that has eventually been accepted as standard.

[John M0GLN]

The other thing is, if 6.3V and its multiple of 12.6V were based on the lead acid battery voltage, why are '12V' power supplies 13.8V?, or am I going OT?

John

[Herald1360]

12V PSUs are 13.8V because this is the float charge voltage for 12V lead acid accumulators.

The cyclic charge voltage to recharge as fast as possible to 100% is around 14.4V; a multistate charger will charge at 14.4V until the charge current falls away to a lowish value, then drop back to 13.8V to keep the battery fully charged indefinitely. Really good ones will monitor the battery to fine tune the voltage with temperature too. For a cheap "safe" single voltage to apply to a 12V accumulator, 13.8V is a good bet.

I suspect a lot of 13.8V "12V" PSUs were intended for mobile application CB rigs, audio amps and the like where an extra volt would make a noticeable difference to the amount of output power available. The equipment has to be able to stand this voltage (and a bit more) when the vehicle is running, so why not get as much out in a fixed application as possible?

So.... why isn't that heater voltage 6.9V? Presumably because 6.3 is also about the middle of the overall range of voltage expected from a 6V accumulator over all its states of charge from cyclic fill up to off charge nearly flat.

Chris

[mickjjo]

I think these odd numbers are explained by the characteristics of lead-acid batteries:-

http://en.wikipedia.org/wiki/Lead-ac..._common_usages

12.6 V is the average figure during discharge and 13.8 V is the figure for freshly charged or "float" charging.
In the case of 2 volt valves the 2.1 volt figure usually becomes 2V at the valve pins due to the resistance of the connecting leads.

Regarsds, Mick.

[John M0GLN]

I posted the link to Renard Numbers as it seemed it might be the answer to the number 6.3 when used for valve heaters, however it looks more likely to be the battery voltage now, it would be much more logical to choose the heater voltage to suit available supplies than to conform to some mathematical table, especially in the 1930s. Perhaps more modern components like 6.3A fuses would now be chosen to suit ISO specs etc.which would probably take into account standard numbering systems like Renard's.

John

[ENGLISH VICTOR]

I believe the Amercans introduced 6.3V heaters first (RCA) the voltage was chosen carefully in order that the valves would operate properly not only when the vehicle was moving but also when stationary i.e. engine not running. The voltage of a well charged battery will only stay at 6.8 V for a short time when the charger is not operating and will quickly level out at aprox 6.3 V for most of the dischage period very slowly dropping over the plateu period to about 6.0 volts then it will rapidly drop and the start of the rapid drop is considered the end voltage, below which it should not be discharged.
The cathodes were designed to operate well at 6.3V and tolerate 6.8V without reducing the life of the cathode noticably. The last statement may be true of radio valves only, T.V. and industrial types may not be so forgiving.
This info was gleaned from an early RCA receiving handbook, it is not verbatim however. The last sentence is mine.
Victor.