# Tag Info

21

When vacuum tube radios were invented, only a fraction of houses had mains electricity, therefore, first radios (and their tubes) were battery powered, they used three batteries: "A" battery for heaters. As heaters require a lot of power, this was a rechargeable battery. A 6V lead-acid battery usually is at 6.3V, so this voltage was chosen as standard. "B" ...

10

Replace the 7805 with a 1Amp or more adjustable regulator and set it to 4.2 volts. Run both the arduino and everything from that instead of running it off the 5V. The Arduino will be fine with 4.2 volts without any issue, and it makes it easier since you dont have to worry about level translation for the input lines either.

9

The electron wouldn't get very far, the mean free path in air would be very short or around nm's before it would collide with an air particle. This would lower the current of the 'open air' electron tube significantly. You might be able to overcome this by shortening the distance between anode and cathode or by raising the voltage of the 'tube'. The point ...

8

You can't. It's not worth it. Tube TVs are so old our local Goodwill won't even take them. You shouldn't. There are dangerous high voltages. This isn't a project to start with.

8

This guy built diodes and triodes that operate in a flame. I think that's about as close to open air as you can get. You could, of course, move to the moon and do your experiments in the great outdoors. The "open air" there is a pretty good vacuum. Here's a picture of a flame triode:

7

There are two types of heaters. In one, the cathode is a hollow cylinder and the heater is inside the cathode but electrically isolated from it and everything else. In the other type, the cathode is a wire with at least two connections. Current is passed thru this wire to heat it while its common mode voltage is driven with whatever signal is supposed to ...

6

The normal rating for vacuum tube heaters is 6.3 volts and 12.6 volts. The 12.6 heaters normally give an option for a centre tap so they can be connected as two 6.3V. There was always a debate about which was best A.C or D.C. but the original amplifiers were wired as A.C. The perceived benefit of rectifying was to reduce hum but the rectified power still ...

6

Is it possible to use a 2.4GHz magnetron as a oscillator for a Tesla coil? The short answer is no, definitely not. The long answer is... well, long. Note that the following reasons are each, by themselves, absolute show stoppers. Only one of them would need to be true to make a 2.4 ghz Tesla coil totally impractical. Unfortunately for this idea, the ...

5

A thyratron (especially a large one) is an example of a pretty rugged device that is quite expensive and difficult to replace with a solid-state device. For example, these hydrogen thyratrons will switch over 10 MW of power - tens of amperes at 25kV switched in less than 1usec, at a peak current of 1000A. Some such devices are used at 100kV. Usually ...

5

So looking at this: What the Pre-Ionized Gap (PIG) and the Thyratron (T) form is a spark-gap flyback impulse generator. Pretty much the same kind of deal that Hertz used to prove the existence of wave propagation, just much, much more precise, shorter, higher energy impulses, and also, the flyback energy is used to excite a laser. So, if you stick with ...

5

An X-ray tube might require 100kV. A current of only 1A would be 100kW, which is a fairly large amount of power even for a water cooled tube with rotating target. The efficiency using a tungsten target would be less than 1%, so most of the power goes into heat. There's no need to produce more X-rays than required, however CT scans may require something of ...

5

There are many different ways that you can get hum in an amplifier, and its hard to troubleshoot without the amp at hand. But generally; hum can enter in three ways: Directly, inductively or capacitively coupled. Looking at your case; did you try to short the reverb return input at the amp when disconnecting the reverb. If the hum is still present, the ...

5

Those few turns look to be a "gimmick" capacitor. Should behave as small (a few pF) capacitor between plate and grid. Provides some degree of negative feedback at high frequencies. Given the relatively high Miller capacitance of the triodes I'm not sure it has a lot of effect. What effect it has will also be dependent on the impedance connected to the I/P ...

4

The other answers are correct; tubes can be heated with either AC or DC. Traditionally AC was used for economic reasons - it saved the expense of a rectifier - except in low power (battery) equipment - which wouldn't apply to a guitar amp. Now with AC heating, there will be some small variation in cathode temperature across the AC cycle, and this modifies ...

4

It's common to run these things from the mains supply. It can be done like so: simulate this circuit – Schematic created using CircuitLab I've skipped some of the detail, but essentially two back-to-back transformers will do it. Pay attention to the way they are arranged. You'll want some smoothing and filtering things after the bridge, and ...

4

There are several types of biasing in tube amplifiers. Your schematic shows one particular type, grid-leak biasing. Grid-leak biasing is by far the hardest to understand, and many erstwhile explanations expect you to push the "I Believe" button and go on. At first blush, it does seem magical: How can the grid get negative with respect to the cathode, ...

4

I was studying tube designs as a child, long before I had any clue how a grounded cathode amplifier might be designed. Which means I don't remember that much. But one thing I do recall, which had bothered me a lot back then, is the ability of a grid to self-bias. You might look up "grid leak resistor," or something similar. A vacuum tube's cathode may ...

4

The Atmega microcontroller in the Arduino will run fine at 4V, so the simplest solution would be to power the whole thing from a 4-4.2V switching power supply instead of using a voltage regulator. Since 4.2V is the end of charge voltage of LiIon cells, there are plenty of off the shelf 4.2V power supplies available. Failing that, you can use a SMPS or wall ...

3

Triodes can work with positive grid voltages but are very rarely operated that way except in power amplifiers. Grid current will flow when the input is positive which can cause distortion and if enough grid current flows the grid can heat to the point of causing damage. It is also not possible to reduce the anode current below the quiescent value using ...

3

A glass fuse works by breaking the circuit when rated current passes through it. When the current passing through the fuse exceeds the rated current, the thin wire melts and breaks the circuit. The glass fuses commonly come in various types: Fast Blow Normal Slow blow Glass fuse does not contain any gas AFAIK. The glass tube protects the outside ...

3

In most amps, valves can be heated with AC or DC. Tapping the heaters may be important since the heater filaments can act like a diode if the cathod is some volts above heater potential (which is the case most of the time with auto bias) and induce AC hum in you beloved signal. Make the heaters center tapped +15V above low signal tubes' cathode can prevent ...

3

These fluro torches typically have very basic inverters in them. the ones I've owned didn't even use the heaters instead treating the tube as cold-cathode and igniting it by breakdown. I don't think that's very good for the tube.

3

I am assuming that the input voltage that feeds the 7805 regulator is significantly higher than 5V. If so, I would use a small adjustable SMPS Buck Regulator that operates from that input supply. You can either build one yourself or simply purchase one of the very inexpensive boards / modules from your favourite supplier. Set the output voltage to the ...

3

GS Tube doesn't make the FEU49B, or any other tube. They sell new old stock Soviet produced vacuum tubes. The datasheets are therefore difficult to read - I know English and German, but no Russian. As I understand your question, you are looking for the pins for "Photo cathode" and "Modulator," and can't find them on the pins that go into ...

3

Looks like you can just swap it out and trim the bias to be the same as it was before. The bias has more than a 10:1 range. The voltage drop of a selenium rectifier depends on how many plates it has.

2

A vacuum tube device's heater filament can be supplied with either DC or AC, the tubes work the exact same way with either type of supply: The heater is simply using the power for resistive heating. The voltage to be supplied would also be the same, i.e. if a tube is rated for 12 Volts, then one uses 12 Volts DC or 12 Volts AC. On the second part of the ...

2

You need to be a little more specific as to which model you're dealing with. You also need to be really careful. If this tube TV uses vacuum tubes on its main circuit board, troubleshooting can be as easy as identifying blown tubes, sourcing replacements and plugging them in. If this is a solid-state TV with only the picture tube as a tube, debugging may ...

2

If it is not exposed to the water, then it is used to make ozone and kill all airborne bacteria and virus and oxidize any organic compounds. It works fine for that and UV lamps are using in bio-labs and lots of places where they need to destroy organics. There used to be mercury vapor lamps in clothes washers and they did not need the high voltage. ...

2

Sounds like a UV lamp, for water sterilization purposes. Don't look at it for too long.

2

A low pass filter is pretty much defined by the R and the C value: - $f_C = \dfrac{1}{2\pi R C}$ The same applies for a simple RC high pass filter and the steepness of the transition from "pas" to "reject" frequencies is very shallow: - Even if the cut-off frequency did fluctuate by (say) 1% (and likely very slowly due to warming and cooling effects of ...

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