Does anyone here know why we settled on 6.3 V of all things? -Why not 6.0, or 3.1416 V? Some of the other higher "unusual" voltages I can almost understand, being more relating to current than voltage for series strung filament applications ("All American 5" design, Muntz TV receivers etc). But the unusual, seemingly random 6.3V seems an odd choice.
There has just got to be a good story behind this one...?
There has just got to be a good story behind this one...?
I'm guessing, but I think it has to do with battery voltages. Some portable tube radios and other equipment had two or more batteries. One battery was the cathode heater, called the "A" battery. Another battery, the "B" battery was a high voltage battery for the plates. It made sense to make the tubes have the same filament voltage rather than make another set of tubes for mains power (aside from the transformerless sets).
Many receivers/amplifiers had an isolated 5volt winding for the rectifier tube. Not sure of the "why" on this voltage selection.
Many receivers/amplifiers had an isolated 5volt winding for the rectifier tube. Not sure of the "why" on this voltage selection.
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5.0V heaters were used with early battery tube, using 6.3V batteries and a rheostat. This allowed a little more life per charge, since the rheostat could be adjusted as the battery voltage dropped... RCA later standardized on multiples of 2.5V for AC tubes: 2.5, 5, 7.5, 10V - they may have been thinking about using an integer number of turns on transformers, and all voltages could be EXACT. A radio often had three transformer windings - 2.5V for small-signal tubes, 2.5V or 7.5V for output tube(s) and 5.0V for the rectifier. The higher power tubes like 10, 50 were 7.5V, no matter since they had their own heater winding... but the small-signal tubes could still add up to 10A or more! Philco had other ideas - they built car radios using 6.3V tubes and decided to use the same ones in their AC powered radios. They bought from Sylvania, not the enemy (RCA), and Sylvania was happy to provide whatever they wanted. Fewer parts to stock and all that... guess whose idea worked out?
Early radios that used Directly Heated tubes did have a rheostat (pot with only two terminals) in series with the filaments. There were three reasons for this. Some times a radio would use a "wet cell" (rechargeable lead acid) for filament power, and other times the same radio could be powered by a "dry cell" (primary carbon zinc) in areas where there was no line voltage to recharge the batteries. The rheostat was used to adjust for battery charge, battery type, and even radio volume. The early DHT's would handle this.
By the time indirectly heated tubes were becoming popular most people had access to electricity to recharge batteries, and radios found their way into automobiles. Although there were some oddballs just about every automobile produced from the late 20's to the early 50's used a 3 cell lead acid battery, which produces 6.3 volts nominally. So if you wanted to pick a voltage that would make everybody happy........
By the time indirectly heated tubes were becoming popular most people had access to electricity to recharge batteries, and radios found their way into automobiles. Although there were some oddballs just about every automobile produced from the late 20's to the early 50's used a 3 cell lead acid battery, which produces 6.3 volts nominally. So if you wanted to pick a voltage that would make everybody happy........
Great thread kruesi.
Knowing how early electronics was controlled by practical concerns, I would expect that there were requirements for heater power. Bigger tubes needed more cathode heating - more heating needed more amps, more amps caused more losses. It's a power transfer thing?
Any ex-Sylvania employees out there?
Knowing how early electronics was controlled by practical concerns, I would expect that there were requirements for heater power. Bigger tubes needed more cathode heating - more heating needed more amps, more amps caused more losses. It's a power transfer thing?
Any ex-Sylvania employees out there?
It's really sounding like the 6.3V choice was from lead-acid cell voltages- dunno why this never occurred to me. Although many pre-war radio circuits I've looked at are powered from A, B and C cells, I guess I'm too used to powering everything from the line.
In my post above I mention the C cell battery pack... I of course meant the "A" cell- we're talking filament voltage here, not grid bias(!) -My oversight.
Tom- I had no idea all the stuff about 2.5, 5, 7.5 ... ever existed! I do recall old transformers having a number of different filament windings, but never put two and two together. Thanks!
And tubelab- you've cleared up the mystery of that huge rheostat- I've seen TRF sets using type 12A directly heated triodes with a large rheostat in series with the filament supply- and here I thought it was just a particularly strange way of doing the volume control. Makes sense to be able to adjust for whatever supply one had available in the days before the completely-standard power grid we have today.
In my post above I mention the C cell battery pack... I of course meant the "A" cell- we're talking filament voltage here, not grid bias(!) -My oversight.
Tom- I had no idea all the stuff about 2.5, 5, 7.5 ... ever existed! I do recall old transformers having a number of different filament windings, but never put two and two together. Thanks!
And tubelab- you've cleared up the mystery of that huge rheostat- I've seen TRF sets using type 12A directly heated triodes with a large rheostat in series with the filament supply- and here I thought it was just a particularly strange way of doing the volume control. Makes sense to be able to adjust for whatever supply one had available in the days before the completely-standard power grid we have today.
Bad form for me to post two replies in a row- but Iain brings up a valid point, one that Tom touched on- I'd expect higher-power tubes (ones that require more emission) to perhaps have higher filament voltages than small-signal stuff- it only makes sense.
Indeed, any rememberances from ex-Sylvania (or indeed ANY tube manufacturer employees) would be gladly welcomed!
Indeed, any rememberances from ex-Sylvania (or indeed ANY tube manufacturer employees) would be gladly welcomed!
6.3V comes from the acid-lead days. 3 elements will provide exactly 6.3V nominal voltage.
It is also a series of TV tubes that work with constant curent (eg 300mA), all the heaters connected series directly to the power main. The bigger tubes (higher power for the heater) had a bigger voltage drop on the heater, smaller ones had a smaller voltage drop. The rest was disipated with power resistors. In this way the TV set didn't need a transformer, just a rectifier and thus was able to work on DC and AC power networks (was called "universal"). And was way lighter.
In european system, the tubes with 6.3V heaters are having the first letter E, the ones with 300mA have P (eg. ECL versus PCL). Some of the smaller 6.3V tubes where manufactured to draw a 300mA curent, so they could work on any place (I saw ECC83 series with P type of tubes). Type P was very popular in TV sets working directly at 220Vac.
First letter in tube numbering in european system:
http://www.duncanamps.com/technical/tubenumber.html
It is also a series of TV tubes that work with constant curent (eg 300mA), all the heaters connected series directly to the power main. The bigger tubes (higher power for the heater) had a bigger voltage drop on the heater, smaller ones had a smaller voltage drop. The rest was disipated with power resistors. In this way the TV set didn't need a transformer, just a rectifier and thus was able to work on DC and AC power networks (was called "universal"). And was way lighter.
In european system, the tubes with 6.3V heaters are having the first letter E, the ones with 300mA have P (eg. ECL versus PCL). Some of the smaller 6.3V tubes where manufactured to draw a 300mA curent, so they could work on any place (I saw ECC83 series with P type of tubes). Type P was very popular in TV sets working directly at 220Vac.
First letter in tube numbering in european system:
http://www.duncanamps.com/technical/tubenumber.html
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this topic has been discussed here : http://www.diyaudio.com/forums/tubes-valves/65332-heater-voltage-why-ac-not-dc.html
roughly 5 years ago....
roughly 5 years ago....
Although we take it for granted, low-voltage rectification is a modern invention, made possible by inexpensive and efficient silicon rectifiers. Before that, all that was available were hideously inefficient (thus very, very hot) Tungar rectifiers, which only saw industrial use.
This has implications for heaters and filament design. The radios of the early Twenties had no connection to the AC line at all; there were separate batteries for bias (A), plate voltage (B), and filaments (C). Although domestically unpopular, owners lugged the heavy lead-acid batteries to a service station for a weekly charge-up. There were contemporary articles complaining about holes in the carpet from battery-acid dripped on the carpet when the batteries were moved from set to car to service-station and back again.
The big breakthrough was the invention of the dedicated high-voltage rectifier tube, which made the AC-powered radio possible, changing radios from a hobby for crazy enthusiasts (like modern DIY audio) to something anyone could enjoy - if you could afford the radio, that is.
Radios in the late Twenties were priced from $70 to $300, but that's in pre-inflation dollars - equivalent to 10 to 20 times that in modern dollars. Time payments were invented so people could buy this must-have appliance on time - although very expensive, it was one of those things you just had to have, much like the Internet today. Back then, it was the only source of instant news, and free music and entertainment as well.
It made the all-mechanical wind-up phonograph look - and sound - pretty stodgy and out-of-date. Record-making was converted to the new "electrical" method in order to compete with the superior sound of the radio, not the other way around. Eventually, mechanical phonographs were replaced by combination units that combined better-quality electrical pickups with radio cabinets - I'm not too sure any stand-alone electrical phonographs were made during the Thirties. The radio was the star of the show, not the phonograph, which was seen as old technology.
What's interesting is that the radio business is one of the very few that continued to grow even during the Great Depression, along with sound movies. Radio, and aviation, were the cutting-edge technologies of the day.
Returning to the A and C voltages, the A voltage was made unnecessary by the advent of cathode bias (with AC-derived high voltage, you can afford to waste a bit of power), and the C voltage was simply 6.3 VAC from a transformer secondary. The indirect-heated tube was invented to get rid of the hum in low-level stages, and it didn't matter in the power tube, which took somewhat longer to convert to indirect heating.
This has implications for heaters and filament design. The radios of the early Twenties had no connection to the AC line at all; there were separate batteries for bias (A), plate voltage (B), and filaments (C). Although domestically unpopular, owners lugged the heavy lead-acid batteries to a service station for a weekly charge-up. There were contemporary articles complaining about holes in the carpet from battery-acid dripped on the carpet when the batteries were moved from set to car to service-station and back again.
The big breakthrough was the invention of the dedicated high-voltage rectifier tube, which made the AC-powered radio possible, changing radios from a hobby for crazy enthusiasts (like modern DIY audio) to something anyone could enjoy - if you could afford the radio, that is.
Radios in the late Twenties were priced from $70 to $300, but that's in pre-inflation dollars - equivalent to 10 to 20 times that in modern dollars. Time payments were invented so people could buy this must-have appliance on time - although very expensive, it was one of those things you just had to have, much like the Internet today. Back then, it was the only source of instant news, and free music and entertainment as well.
It made the all-mechanical wind-up phonograph look - and sound - pretty stodgy and out-of-date. Record-making was converted to the new "electrical" method in order to compete with the superior sound of the radio, not the other way around. Eventually, mechanical phonographs were replaced by combination units that combined better-quality electrical pickups with radio cabinets - I'm not too sure any stand-alone electrical phonographs were made during the Thirties. The radio was the star of the show, not the phonograph, which was seen as old technology.
What's interesting is that the radio business is one of the very few that continued to grow even during the Great Depression, along with sound movies. Radio, and aviation, were the cutting-edge technologies of the day.
Returning to the A and C voltages, the A voltage was made unnecessary by the advent of cathode bias (with AC-derived high voltage, you can afford to waste a bit of power), and the C voltage was simply 6.3 VAC from a transformer secondary. The indirect-heated tube was invented to get rid of the hum in low-level stages, and it didn't matter in the power tube, which took somewhat longer to convert to indirect heating.
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I'm confused, my understanding is that "A" batteries heated filaments, and "C" batteries provided grid bias. Old battery radios that I have owned followed this convention. Typo?
Filament Voltages
In America, 2.5V AC was chosen for the filament voltage for AC-operated sets, since this produced the least hum in DHT output tubes as well as less electrostatically-coupled hum in heater-cathode types. In a big radio, the filament wiring could become massive, due to the high currents involved.
As car radios started to become popular in the early 1930s, 6.3V versions were made that would run off of the 3-cell lead-acid battery under charge. Once directly-heated triodes and pentodes were replaced by heater-cathode types, the radio manufacturers started to use the 6.3V types since the heater currents were lower. Also, the very first transformerless (AC/DC) radios could use the 6.3V 0.3A tubes in series along with big dropping resistor.
Even in the 1930s, some cars and trucks used 6-cell lead-acid batteries, so 12.6V versions of common radio tubes were made. Since these usually had 0.15A heaters, they could be strung in series much more economically than 6.3V tubes, which lead to the classic "All-American Five" radio line-up of the late 1930s: 12SA7, 12SK7, 12SQ7, 50L6GT, and 35Z5GT which could all be strung in series without a dropping resistor (on a 117V line). The loctal version was: 14Q7, 14A7, 14B6, 50A5, and 35Z3. After the war, these were slowly replaced by the miniature All-American Five set: 12BE6, 12BA6, 12AT6, 50B5, and 35W4. The 12AT6 was later replaced by the higher-gain 12AV6 and the 50B5 was replaced by the 50C5 for UL-compatibility reasons.
The first television sets were transformer-operated and used 6.3V tubes. By the late 1940s, some manufacturers were experimenting in making "series-string" sets, thus eliminating the power transformer, but these were not very reliable, since the different heating times of the different tube put heavy stress on the fastest heating tube (compare a 12W4GT damper diode to a 6AL5 signal diode, for example). By the end of the Korean war, there was severe pressure to reduce costs and reduce the use of strategic materials, so a big push was made by the tube companies to make series-string sets reliable. One result was establishing a standard 11-second warm-up time. Since TV sets used either 0.6A or 0.45A heater currents, there was an explosion of crazy-voltage tubes (i.e. 3AU6, 4AU6, 6AU6) that vastly increased the number of tubes a serviceman had to stock.
As a last-gasp to increase the efficiency of 5-tube radios, in 1958, Sylvania came up with a 0.1A version of the All-American Five: 18FX6, 18FW6, 18FY6, 32ET5, and 36AM6. RCA and Westinghouse also introduced some 0.1A versions. Although more efficient, these types didn't really catch on, since they were slightly more expensive than the standard 0.15A types, and saving a few pennies in manufacturing costs was more important than saving many dollars in the customer's power bill.
The history above is of the American scene. In the UK and Europe, 4 volts was chosen for the standard AC heater voltage, and since it was less difficult than the American 2.5V system, stayed in use up until and shortly after the war. Europe also had different series-string currents - generally 0.1A for radios.
- John Atwood
In America, 2.5V AC was chosen for the filament voltage for AC-operated sets, since this produced the least hum in DHT output tubes as well as less electrostatically-coupled hum in heater-cathode types. In a big radio, the filament wiring could become massive, due to the high currents involved.
As car radios started to become popular in the early 1930s, 6.3V versions were made that would run off of the 3-cell lead-acid battery under charge. Once directly-heated triodes and pentodes were replaced by heater-cathode types, the radio manufacturers started to use the 6.3V types since the heater currents were lower. Also, the very first transformerless (AC/DC) radios could use the 6.3V 0.3A tubes in series along with big dropping resistor.
Even in the 1930s, some cars and trucks used 6-cell lead-acid batteries, so 12.6V versions of common radio tubes were made. Since these usually had 0.15A heaters, they could be strung in series much more economically than 6.3V tubes, which lead to the classic "All-American Five" radio line-up of the late 1930s: 12SA7, 12SK7, 12SQ7, 50L6GT, and 35Z5GT which could all be strung in series without a dropping resistor (on a 117V line). The loctal version was: 14Q7, 14A7, 14B6, 50A5, and 35Z3. After the war, these were slowly replaced by the miniature All-American Five set: 12BE6, 12BA6, 12AT6, 50B5, and 35W4. The 12AT6 was later replaced by the higher-gain 12AV6 and the 50B5 was replaced by the 50C5 for UL-compatibility reasons.
The first television sets were transformer-operated and used 6.3V tubes. By the late 1940s, some manufacturers were experimenting in making "series-string" sets, thus eliminating the power transformer, but these were not very reliable, since the different heating times of the different tube put heavy stress on the fastest heating tube (compare a 12W4GT damper diode to a 6AL5 signal diode, for example). By the end of the Korean war, there was severe pressure to reduce costs and reduce the use of strategic materials, so a big push was made by the tube companies to make series-string sets reliable. One result was establishing a standard 11-second warm-up time. Since TV sets used either 0.6A or 0.45A heater currents, there was an explosion of crazy-voltage tubes (i.e. 3AU6, 4AU6, 6AU6) that vastly increased the number of tubes a serviceman had to stock.
As a last-gasp to increase the efficiency of 5-tube radios, in 1958, Sylvania came up with a 0.1A version of the All-American Five: 18FX6, 18FW6, 18FY6, 32ET5, and 36AM6. RCA and Westinghouse also introduced some 0.1A versions. Although more efficient, these types didn't really catch on, since they were slightly more expensive than the standard 0.15A types, and saving a few pennies in manufacturing costs was more important than saving many dollars in the customer's power bill.
The history above is of the American scene. In the UK and Europe, 4 volts was chosen for the standard AC heater voltage, and since it was less difficult than the American 2.5V system, stayed in use up until and shortly after the war. Europe also had different series-string currents - generally 0.1A for radios.
- John Atwood
Well now there's something ELSE that's new to me- the European numbering system! Not that I was unaware of it- I was- but I really didn't know it was a regular system that describes the tube's characteristics.
It actually makes sense, as opposed to the American system in which only the first and last numbers really mean anything. I still have no idea what the middle two letters mean in most tube numbers or how they were chosen- perhaps the initials of the engineer that led the development effort for that type.
But that's a subject for another thread (!)
It actually makes sense, as opposed to the American system in which only the first and last numbers really mean anything. I still have no idea what the middle two letters mean in most tube numbers or how they were chosen- perhaps the initials of the engineer that led the development effort for that type.
But that's a subject for another thread (!)
It is as regular as grampa on laxatives 
There are few exceptions that make matters confusing, especially because one such exception pertains to the naming of immensely popular output tube.
Enjoy: How to decode European valve numbers
There are few exceptions that make matters confusing, especially because one such exception pertains to the naming of immensely popular output tube.Enjoy: How to decode European valve numbers
According to my old basic radio course book, you are correct. "A" battery is for the filaments...
Unless my collection of old radios are all wrong, that is the case. And as mentioned before the "C" battery (bias) dissapeared. It seemed to go away about the same time the "battery" tubes (1C5, 1N5, 3Q5 etc) came out. In many cases "portable" radios used one dry cell battery that had both the A and B cells inside it. The Zenith Transoceanic come to mind, but there were much earlier examples.
Yep- The Transoceanic was one, likely the "Tom Thumb" (I forget the Mfr) was another. Burgess made a long line of combination dry cells at one time. I also have seen line powered PA amplifiers that used tiny button-sized zinc-carbon 1.5V cells for the "C" supply. Everything else was line-operated with no provision for any other batteries. Weird. Why they didn't use cathode bias, I'll never know...
I'm overwhelmed to realize that all these years (I'm 58, born 1951) I never imagined all these old TRF sets and other early radios being operated from batteries (and lead-acid, at that). Always assumed (!!) they were all line operated. But now that I consider the state of electrification in 1925, it seems obvious! Duh...
I'm overwhelmed to realize that all these years (I'm 58, born 1951) I never imagined all these old TRF sets and other early radios being operated from batteries (and lead-acid, at that). Always assumed (!!) they were all line operated. But now that I consider the state of electrification in 1925, it seems obvious! Duh...