Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: supro66 on February 25, 2015, 11:54:57 am
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this might be a dumb question
why do you need 5 volts for a rectifier tube and 6 volts for other tubes :dontknow:
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this might be a dumb question
why do you need 5 volts for a rectifier tube and 6 volts for other tubes :dontknow:
Because a 5xx tube needs 5v and a 6xx tube needs 6v. However, some rectifier tubes operate on 6 v, for example, EZ81, or 6X4.
But more important, most 5xx rectifier tubes have their cathode directly connected to the filament. Some even put a special coating on the actual filament wire and this acts as the cathode. This means that full B+ will also be on the filament winding and this means you will have to heat all the other tubes with a separate winding.
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I understand the two separate power supply's but why 5 volts and not two 6 volts
then there is the 12AX7 [ 12 volts and 7 components ]
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I understand the two separate power supply's but why 5 volts and not two 6 volts
then there is the 12AX7 [ 12 volts and 7 components ]
Why are some light bulbs rated for 3, or 6, or 12, or 14, or 28, or 48, or 120 volts?
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"I understand the two separate power supply's but why 5 volts and not two 6 voltsthen there is the 12AX7"
The biggest reason (guess) is that full on unfiltered B+ shows up on that filament in a (for example) 5Y3 or a 5U4!! That's where you take your tube-rectified B+ from isn't it? This is nasty, pulsating DC high volts and high current with a ton of ripple and the last place you'd want it would be on the heater of your supposedly nice quiet 12AX7. A 12AX7 has a heater-to-cathode "do not exceed" rating of 120 or 140 volts IIRC and most people stay well under that. You would easily have that much in ripple right at the rectifier tube heater. Never mind the noise, you could blow that 12AX7 to smithereens, which would then short out your power supply, or place your power supply across a 1500 ohm resistor. Assuming 450 volts at the rectifier heater thru 1500 ohms, that's .3 amps. .3 * .3 * 1500 ohms = 135 watts. That resistor would vaporize. If the 12AX7 had no cathode resistor it would fry, fast.
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My guess it is the old question
What came first
The Rectifier tube or the amplification tube
Lee De Forest started this game it goes back to then ,they must of had a better source of 5 volts
or they just pulled it out of the air
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My guess it is the old question
What came first
The Rectifier tube or the amplification tube
Lee De Forest started this game it goes back to then ,they must of had a better source of 5 volts
or they just pulled it out of the air
The diode (rectifier) came first. Fleming was playing with this stuff 10 years before De Forest.
http://www.pbs.org/transistor/science/events/vacuumt.html (http://www.pbs.org/transistor/science/events/vacuumt.html)
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> why do you need 5 volts for a rectifier tube and 6 volts for other tubes
6.3V is SO modern.
That's about Car Radio, a big fad in the 1930s. Big enough that older tubes were changed to 6.3V.
But look at the pre-car tubes. The now-forgot '27, '35, and '57 are 2.5V. 2A3 is still around, 2.5 Volts. (And never from a battery!)
2.5V was VERY common on US line-powered radios. You want a voltage which is not-large (to reduce hum), but not-tiny (so you don't need massive wires). 2.5V became somewhat standard, but other voltages were used also.
In England, after some flailing-around with 1-cell (2V) and 3-Cell (6V), 4V (2-cell, but usually AC) became the common heater voltage. Just different, no specific reason; there was very little cross-Atlantic tube-trading until the late 1930s, and by then the advantage of settling on 6.3V were obvious to all. (English cars used 12V batteries whereas US was 6V, but you can easily stack 6V tubes to a 12V source.)
There is a line of 2V tubes (single lead cell).
There are 1.4V tubes (flashlight cell).
> why do you need 5 volts for a rectifier tube and 6 volts for other tubes
Nearly all the rectifier tubes really date to pre-6.3V days. And there is NO reason the rectifier needs to be the same as the other tubes, because a rectifier filament normally sits near B+ and can't share a circuit with signal tubes who run cathodes down near B-/ground. And rectifier can be the biggest heater in the cabinet. I think they doubled-up the standard 2.5V heater for double-output thus 5V.
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Thank you all
I have a friend who has boxes of old TV tubes he thinks they are worth money
I told him most of his tubes are useless
the circuits for these tubes do no exist any more, sweep tubes, Hoz stabilizer,
he has two big tubes that came out of some old industrial boring mill even in China they don't use them
I told him he could make book ends out of them
Back in the old days I asked a teacher a question I got
Because I say so
the teacher said the Area of a circle was
Pi R squared
I said no
Pies are round :laugh:
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I saw someplace Edison kind of invented the Tube
In the course of his experimentation (sometime around 1883), Edison placed a strip of metal inside of an evacuated (vacuum) glass bulb along with the filament. Between this metal strip and one of the filament connections he attached a sensitive ammeter. What he found was that electrons would flow through the meter whenever the filament was hot, but ceased when the filament cooled down:
http://www.allaboutcircuits.com/vol_3/chpt_13/2.html
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Edison invented the rectifier, but did nothing with it.
He was trying to keep his lightbulbs from blacking themselves out. The hot filament emitted soot, coating the inside of the bulb. He placed a second piece of metal inside the bulb, and found when a certain polarity voltage was applied (with respect to the filament) a current flowed between the two. Edison thought it was an interesting occurrence, but it didn't solve the soot problem.
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It's not really a topic for debate, but historical fact.
That said, someone else discovered emission first, Edison called his discovery the "Edison Effect," but it took Fleming and DeForest to create the first useful vacuum tubes.