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Old 10th June 2013, 08:28 AM   #1
M Gregg is offline M Gregg  United Kingdom
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Default Why 6.3V?

Simple question,

I guess someone knows..

Why are heaters 6.3V....ie why the .3? not six volt. or even 6.5V..

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Old 10th June 2013, 08:38 AM   #2
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3X lead/acid storage cells in series. Remember, that 6.3 V. is nominal. Most types are OK plus or minus 10%. Plus or minus 5% is "never" problematic.
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Old 10th June 2013, 08:44 AM   #3
M Gregg is offline M Gregg  United Kingdom
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I thought about the batteries..

Then I thought ..when was it decided to make it a standard and why, was it portability..or something else?
Ie was battery power the first idea? Or was it Tx power.
I found this interesting..(its not the answer though)..but the dates are..

http://www.ee.umd.edu/~taylor/Electrons3.htm

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Old 10th June 2013, 09:51 AM   #4
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My old radio is powered by a 2V and a 70V battery.

There was no mains power at many homes when the radio era started so TX wasnīt an option.

Since my local grocery store has stopped selling anode batteries itīs now converted to mains power .
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Old 10th June 2013, 01:03 PM   #5
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RCA chose to make AC powered tubes in multiples of 2.5V. This made transformer design easy, as the separate windings could be exact multiples by having 2X or 3x the number of turns. Small signal tubes were generally 2.5V, rectifiers were 5V, the first high power triodes were 7.5V, some transmitting tubes were 10V. But... Philco had other ideas. Philco was the largest radio manufacturer at the time, and made car radios (which used 6.3V tubes) as well as AC powered radios. Why not use the same tubes for both? And since they weren't buying tubes from their competitor, RCA, they had no trouble buying what they wanted. Most companies followed Philco's lead, eventually RCA did as well.
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Old 10th June 2013, 01:15 PM   #6
MikeVou is offline MikeVou  United Kingdom
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Here's a possible answer -

6.3 Volt Valves
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Old 10th June 2013, 01:20 PM   #7
MikeVou is offline MikeVou  United Kingdom
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And an earlier thread, suggesting the same thinking -

Filament voltages - an idle curiosity
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Old 10th June 2013, 01:25 PM   #8
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In a far away land, a long long time ago.....OH, wait that's a different story.

As previously stated many houses, primarilly rural, did not have AC power. The "farm radios" of the day used a rechargeable lead acid battery for the heaters/filaments. B+ and B- were conventional dry batteries.

The heater battery needed replacement/recharging far more often than the others. Often the radio owner took the heater battery down to the local gas station for a swap out when he went to get gas for the car or tractor. The predominant rechargable technology of the day was lead acid at 2.1 volts per cell. Many tubes were 2 volts or less with a variable resistor in series with the filament which could be reduced as the battery drained.

The 3 cell battery (6.3 volts) was quickly becoming the standard in the auto/tractor industry, so the vacuum tube world adopted this voltage as the indirectly heated tube become common. Cars became bigger, with bigger engines. Better gas allowed higher compression ratios which required a bigger, higher torque starter to crank the engine. The battery cables were already 1/2 inch in diameter and getting larger every year. This prompted the auto industry to adopt the 6 cell battery in the 1950's. There was a push by the auto industry to switch to 42 volts a few years ago to reduce the copper content in modern cars, but that seems to have died.

An interesting side note:

I work for Motorola. The company's first product was a "battery eliminator". It was a power supply that operated from household power and generated the A+ (heater power), B+(plate power), and C-(grid voltage) that the "farm radio" needed. The second big product was a car radio. That's when the company changed it's name from Galvin manufacturing to "Motor" "ola", a combination of "Motor Car" and "Victrola".
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Old 10th June 2013, 01:49 PM   #9
TheGimp is offline TheGimp  United States
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You sometimes see 1.5V filaments as well. Zinc-Carbon batteries were 1.5V.

The filament was the "A" battery.

Why do you see a lot of 180 V B+ specs? ....

"B" Batteries were 90V.

2 X 90V = 180V

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Old 10th June 2013, 02:53 PM   #10
MikeVou is offline MikeVou  United Kingdom
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Isn't there a slight problem here?
If you wanted the AC heating equivalent of a 6.3V DC car battery, you would need about 8.9V (assuming sine-wave). Or have I got something wrong?
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