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Old 10th June 2013, 02:58 PM   #11
MikeVou is offline MikeVou  United Kingdom
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No, of course I'm wrong. Provided the 6.3V AC is specified as "rms", they will be the same!
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Old 10th June 2013, 03:00 PM   #12
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Originally Posted by MikeVou View Post
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?
You're right, You've got something wrong. The 6.3 volts is AC RMS so it has equal heating power to DC. The peak voltage is 1.414 x RMS for a sine wave.

The thing everyone seems to have gotten wrong is that the first radios were entirely battery powered! It wasn't until the invention of the electrolytic capacitor that radios could make their own DC from any AC mains.

That then required new tubes that had indirect heaters so you could power the filaments from low voltage AC.

The lower filament voltage tubes that ran on a single cell came later when they were making portable tube radios. Some ran on 1.5 volts others 3 volts. Since they were designed for DC they often used the filament as the cathode. Or at least direct heated.
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Old 10th June 2013, 03:11 PM   #13
fpitas is offline fpitas  United States
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Quote:
Originally Posted by MikeVou View Post
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?
6.3VAC RMS will have the same heating value as 6.3VDC.

Edit: looks like the subject got covered before I posted.

Last edited by fpitas; 10th June 2013 at 03:14 PM.
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Old 10th June 2013, 05:02 PM   #14
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Originally Posted by tubelab.com View Post
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".
PM when you get the chance about next years ham fest in Dayton . As for the conversion to 42 volt I think it as to far if they had gone 24 volt then 2 batteries and an easy way to jump a dead battery set would have been a voltage double diodes with the set with a 12 and 24 volt hook up . That was the problem when in about 55 or 56 they went from 6 to 12 as a mater of fact ford was positve ground in 55. 24 volt is currently used on Semi I understand.

Last edited by Triodethom; 10th June 2013 at 05:09 PM.
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Old 10th June 2013, 10:08 PM   #15
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Quote:
The thing everyone seems to have gotten wrong is that the first radios were entirely battery powered!
This is true, all of the early radios were battery operated.

Quote:
That then required new tubes that had indirect heaters so you could power the filaments from low voltage AC.
Ther first AC operated radios used DH tubes. I have sold off, or given away most of my old radio collection, but there were plenty of AC operated radios going back to the early 20's (and probably earlier) that operate from mains power and use DH tubes.

Quote:
As for the conversion to 42 volt I think it as to far if they had gone 24 volt
We had to write several proposals discussing the costs associated with converting many of our mobile radio products to 42 volts while still supporting the existing user base at 12 volts. This was maybe 5 to 8 years ago.

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24 volt is currently used on Semi I understand.
Most semi trucks do indeed use two BIG 12 volt batteries in series. The current needed to start a big Diesel engine on 12 volts would be outregeous.

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That was the problem when in about 55 or 56 they went from 6 to 12 as a mater of fact ford was positve ground in 55.
My first car was a 1949 Plymouth. It was 6 volts positive ground. It had a Motorola radio that had about 10 tubes and used a pair of 6V6GT's for the output stage. The power amp and power supply was on a seperate chassis, so I got two of them mounted them in the trunk and fed them with a Panasonic portable cassette player. I had the loudest car stereo in high school.

The VW beetles of the day used 6 volts negative ground. There was a step up box that converted 6 volts negative ground, to 12 volts, and I wanted an 8 track player, so I simply turned the battery around so I had negative ground, and installed the booster box. The ammeter worked backwards, but everything else in the car seemed fine including the original radios.

After blowing up two of the booster boxes, I ditched my generator, added an alternator from an old Pontiac, and a voltage regulator from a Dodge Dart, and dropped in a 12 volt battery. I had to replace all the light bulbs, and the gas gauge stayed on full until I had about 3 drops of gas left, but again the car ran normally. The old 6 volt radios, like the light bulbs, had a short unhappy life. I had various solid state stereos in the car in the 20 years that I had it.

I know that a few cars went to 12 volts negative ground in the early 50's. I think Cadillac was 12 volts in 53 or 54. I know the 53 Dodge (Red Ram Hemi V8) we had was 6V but my neighbors 55 Desoto (Firedome Hemi V8) was 12V.
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Old 11th June 2013, 12:26 AM   #16
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Tubelab You cover ever thing nicely as always.
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Old 11th June 2013, 01:01 AM   #17
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My Mother had a "portable" radio she purchased just after WWII. It was the size of a portable typewriter, and was cased in grey bakelight. It used a wet "A" (filament)battery; oddly I remember it being 3 volts something. The A battery was about 3"x3"x10" tall made of glass; you could see the solution sloshing around in it. I think it was exide brand or perhaps Union carbide. It used a dry cell "B" battery, which I remember as being nominal 200 V or something. The B battery was about 2"x2"x6" tall, wrapped in cardboard with the Eveready black cat logo on it. The source of 3 v A batteries and dry B batteries (the company store at the coal mine) dried up by the time of our move in 1956 and my thrifty Mother threw it away in the sixties.
6.3 nominal dry cell "lantern" batteries were extremely common in the fifties and can still be purchased. these were four 1.6 v carbon rod cells in series, IMHO. It works out close enough to 3 wet lead-acid cells at 6.6v, that was used in car radios. So the 6.3 V filiment tube was a good compromise. by 1956 the "vibrator" had been developed to make the B+ voltage in cars, a bimetallic strip that interrupted the battery at an audible frequency to drive a step up transformer. I have a 1956 fomoco radio with vibrator supply that still works reliably (no electrolytic caps). My father had a 1950 chevrolet radio that stopped working in 1952, so the vibrator technology in 1950 was still pretty iffy. I didn't fiind out about the vibrator until I had one go bad in the ford in 1967, and my chemistry teacher taught me about them.
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Last edited by indianajo; 11th June 2013 at 01:08 AM.
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Old 11th June 2013, 01:09 AM   #18
TheGimp is offline TheGimp  United States
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1955 Cheverolet Belair was 6.3V as well. I converted mine to 12.6V by replacing the generator, ingnition coil, radio (the original was AM only), horn, starter, and all light bulbs. Not as difficult as it sounds.

British cars on the other hand were positive ground. Are they still?
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Old 11th June 2013, 02:31 PM   #19
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Quote:
by 1956 the "vibrator" had been developed to make the B+ voltage in cars, a bimetallic strip that interrupted the battery at an audible frequency to drive a step up transformer. I have a 1956 fomoco radio with vibrator supply that still works reliably (no electrolytic caps).
The vibrator supply goes back to the 40's and maybe even the late 30's. My 1949 Plymouth radio had a vibrator and I believe an 0Z4 gas recitfier. The rectifier might have been a 6X5 I am not too sure on that. It's been 40+ years since I tossed them.

I have dismantled several WWII vintage mobile two way radios that use a vibrator supply. The vibrator was not bimetallic, it was totally magnetic. The early ones were crude and worked much like the spark coil in a model T Ford. The later ones were complex and generated a near perfect square wave that needed little B+ filtering. There were two sets of contacts with different spring tension. There was a ferrous weight on the end of the "armature". One set of contacts opearated the internal coils, while the other set fed the external step up transformer. When energized, battery was applied to one coil, attracting the weight at the end of the armature, armature movement broke that set of contacts, and applied battery to the other coil pulling the weight back the other way. Then those contacts opened and the other closed starting the process over.


Quote:
I didn't fiind out about the vibrator until I had one go bad in the ford in 1967, and my chemistry teacher taught me about them.
The vibrator supply was on its way out in the mid 50's. By the late 50's all car radios used "space charge" tubes that ran directly from a 12 volt battery, including the plate voltage. These tubes all have a 12 volt heater and a 30 volt maximum plate voltage. There were a few developed for aircraft use that ran from a 26 or 28 volt heater with a 50 volt plate rating. The audio output power of the space charge tubes was dismal, maybe 1/4 watt, so the radios switched to a big fat germanium transistor for the output stage in the late 50's. I used to get these transistors from dead radios in the mid 60's. I still remember the # 2N174. The later radios used a smaller 2N301.

I also have an old RCA radio. I was told by a collector that it dates from 1929 or 1930. It is a superhet design with minimal RF filtering so it picks up signals corresponding with any of the many harmonics of the local oscillator. This wasn't a problem in 1930, but the radio is pretty useless now. It has a crude wax filled power transformers, and some kind of can capacitors that may be early electrolytics. They were all open, so I paralleled new ones across them. Some of the wax paper coupling caps were shorted, so I replaced them. The radio "works" and picks up dozens of broadcasts, but none of them are in the English language.

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My Mother had a "portable" radio she purchased just after WWII.
Wet cells were common in "portable" radios until the "battery tubes" came out in 1939-1940. These tubes revolutionized the portable radio world. Each ran from a single 1.4 volt supply and consumed only 50 ma of heater current. The audio output tube needed 2.8 volts.

Transconductance was low, and they are highly microphonic, but that didn't matter. The heaters were all wired in series, so a 4 tube radio ran from a 5 cell 7.5 volt battery. Each tube was designed to operate with the bias voltage derived from the heater supply, so a portable radio needed only two batteries. Usually there was a 7.5 volt heater battery, and a 90 volt "B" battery. By the late 40's both batteries were combined. Zenith commisioned a special converter tube that has reasonable high frequency response, so they released the Transoceanic portable with shortwave capability. Good luck finding a good 1L6 converter tube today......both my Transoceanics still have their original tubes and they still work.
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Old 11th June 2013, 08:27 PM   #20
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Originally Posted by tubelab.com View Post
T
Wet cells were common in "portable" radios until the "battery tubes" came out in 1939-1940. These tubes revolutionized the portable radio world. Each ran from a single 1.4 volt supply and consumed only 50 ma of heater current. The audio output tube needed 2.8 volts.

Transconductance was low, and they are highly microphonic, but that didn't matter. The heaters were all wired in series, so a 4 tube radio ran from a 5 cell 7.5 volt battery. Each tube was designed to operate with the bias voltage derived from the heater supply, so a portable radio needed only two batteries. Usually there was a 7.5 volt heater battery, and a 90 volt "B" battery. By the late 40's both batteries were combined. Zenith commisioned a special converter tube that has reasonable high frequency response, so they released the Transoceanic portable with shortwave capability.
The wet cell A, dry cell B portable radio could not have been bought before 1946, as Mother went to work at the mine age 16 in 1943 after secretarial school, and was extremely poor until she'd worked a couple of years. She was shock "graduated" at age 15 in 1942 for learning too fast. We didn't see premium products like the Zenith Transoceanic at the company store in Montcoal, WV; what we got was oddball products nobody else could sell. My first record player was a Bozo the Clown model with a paper diaphragm "amplifier" (no tubes). Nobody up there had ever seen Bozo the Clown on TV. You didn't get TV signals up in the mountains.
The vibrator I replaced in 1967 was in the 1956 fomoco radio, so Dad & I got 6 good years out of it, since it was bought in a 59 Ford in 1961. That 59 ford had a 56 vibrator radio with a ballast resistor (going by the knob design), 1957 Ford hub caps, no sun visor on the passenger side, no door pulls, a real stripper. The 1956 Fomoco radio was negative ground, fortunately. I got my first plate voltage training on that radio, bridging the B+ between my index finger on the meter probe and thumb on the frame. A great shock. The 59 Ford car service manual had no high voltage warning; the schematic in that documented a space charge radio with 12v plates on the tubes and a Ge transistor on the back panel.
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