The basic triode vacuum tube consisting of a filament,cathode,grid,and plate works like a fet such as MPF102. The filament when up to temperature emits electrons. The cathode is the same as the source on the fet. The grid is the same as the gate, and the plate the same as the drain.
I hope this helps

 

From what I have been reading, tubes don't require more than 6 volts to get the filament burning hot (the amount of current is another story) but I think a simple 9 volt battery should light up a number of them when connected in parallel like some houses are weird for switches with more than one fixture ( the figure above the mirror in the bathroom with like 6 bulbs in it)

 

From what I have been reading, tubes don't require more than 6 volts to get the filament burning hot (the amount of current is another story) but I think a simple 9 volt battery should light up a number of them when connected in parallel like some houses are weird for switches with more than one fixture ( the figure above the mirror in the bathroom with like 6 bulbs in it)

Typically the first number of the tube number is the filament voltage 12AX7 has a 12 volt filament. Doubt a 9 volt battery will be able to supply enough current to light even one 6 volt tube.

 

Both 6 and 12 volts were common filament voltages for tubes. Some of the 12 volt units had center tapped filaments so the two halves could be run in parallel on 6 volts. If you look at transformers, 6.3 volts was a common secondary voltage to run those. If you look at some of the tube data sheets, you will see that the filaments were current hungry so your idea of running them on a 9V battery would result in a very short battery life. Back before transistors, portable radios had two battery packs. The A battery ran the filaments and the B battery ran the plate circuits. Also, specialty tubes were available for things like hearing aids. Back then, a hearing aid was about the size of a pack of cigarettes and had a cord from the box to the ear piece.

http://www.hearingaidmuseum.com/gal...nfoVacuumTube/info/generalinfo-vacuumtube.htm

 

We had sub-mini tubes in some of the old crypto devices designed during the 50's. Part of the process of calibration was to adjust the filament and plate voltages to insure proper operation of the feedback registers and noise generators. Most the logic tubes had a filament voltage of 1.25 volts.
http://www.jogis-roehrenbude.de/Leserbriefe/Vico-Pichotka-Mini-Audion/6088.pdf

http://en.wikipedia.org/wiki/KW-37

 

A small 9V alkaline battery has a small maximum current.
Vacuum tube filaments need a high current.
Then you cannot use a 9V battery.

 

Here's the datasheet for arguably the most common preamp tube which is currently in use:
http://www.tubesandmore.com/sites/default/files/assoc_files/t-12ax7_ecc83s-jj_specificationsheet_0.pdf

The filament requires either 12.6 v at 150 ma or 6.3 v at 300ma.
These specs are under base type.
The filaments are pins 4,5 with a center tap at pin 9.
So, how would you connect the filaments to run at 12.6v vs 6.3v??

Also note, this tube is actually two triodes in one package.

 

I liked the little battery-powered 1S5 when I was a teenager. I built a little one tube AM band regenerative receiver (this was in the mid-to-late '50's). It worked great (for a kid) with a long-wire antenna and high-impedance headphones.
The filament required 1.4V @ 50mA, which a D cell provided. The plate supply was a 22.5V hearing aid battery, which lasted for months.
You can still find plans for these receivers on the Internet.

 

4 to 5 with 9 open is 12.6. When 4 is tied to 5 with power between 4-5 and 9 is 6.3
Another usage of the center tap was to use a center tapped 12.6V filament transformer with the center tap grounded. In that case, pin 9 would also be grounded. It reduced the introduction of AC hum in an audio amplifier.

 

Post #21 reflects my sentiment. Tubes are like jfets in that they are normally "on" and must be biased to conduct less than maximum idle current in order to work as class A amplifiers. In both cases, the gate (grid) is not intended to carry current. When the gate or grid does become positive with respect to the cathode (source) it is usually considered to be a mistake or a transient condition. In this comparison you will find similarities that might help you understand tubes.

 

Baron...
If you want to build something, check this out:

http://www.shine7.com/audio/12ax7_pre.htm

Shows how to design a simple preamp. Lots of useful info.
For experimenting regular copper wire is fine......
Also, the gain of 51 is more than needed.
Many typical amps need only approximately 0.7V - 2V input signal for full power.

 

ONE vacuum tube has horrible distortion.
ONE transistor also has horrible distortion.

TWO vacuum tubes have much less distortion.
TWO transistors also have much less distortion.

But when the vacuum tubes wear out the distortion is horrible and their replacement cost is high. Transistors do not "wear out".

 

Didn't further tube developments improve the sound quality, such as pentodes and tetrodes. These were interesting to read about.

 

Didn't further tube developments improve the sound quality, such as pentodes and tetrodes. These were interesting to read about.

Here's some interesting reading regarding pentodes in ultra-liner mode:
http://www.tubecad.com/january2000/page2.html

Pentodes were commonly connected in this mode using tapped output transformers for improved specs. Many hi-fi tube audio amplifiers used and still use this topology.

 

Here's a good link for tube audio circuits:
http://diyaudioprojects.com/Schematics/

 

@tubeguy
delightful read at DIY site
note of caution: the solid state rectifier bridges are often drawn incorrectly.