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Questions tagged [vacuum-tube]

Any device that incorporates an evacuated chamber in which free-floating electrons are manipulated.

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Can I use a laptop backlight inverter as a tube power supply?

I would like to build a circuit that has a magic eye in it. That needs ~290V. I was wondering if I can/should use a CCFL inverter (salvaged from an old laptop) to generate that voltage, maybe driving ...
The Bishop of Canterbury's user avatar
5 votes
6 answers
568 views

Were vacuum tube computers made of logic gates?

A lot of introductory resources on modern CPU present them as being built from NAND gates (see here and there for instance). Actually, it is possible to build a modern CPU using almost exclusively ...
Weier's user avatar
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2 votes
1 answer
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Can a vacuum tube convert tube heat to power

In playing with the triode component in the Falstad simulator, I often observe behaviors that seem nonsensical, with a tube sometimes acting as a power source. If a triode just had three connections ...
supercat's user avatar
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NOT gate using triodes

I can't understand the functioning of the circuit of a NOT gate using a triode (vacuum tube) and a resistance (big rectangle connected between the triode's anode and the positive power supply). For ...
Aleksei Koshelev's user avatar
4 votes
1 answer
1k views

What is this glass bulb containing three parallel electrodes?

I'm trying to figure out what the glass component on the PCB is. Maybe some sort of vacuum tube? Maybe a triac? It's got three leads, and appears to have three parallel electrodes inside the glass ...
gamerboy0295's user avatar
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How to identify an old oscilloscope tube?

I have this tube: There is no manufacturer or part number written on it, only the numbers 50321. The first 5 I'm not sure. Any idea what can it be and what voltages are needed to operate it? It's ...
vjalle's user avatar
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2 answers
75 views

Replace One Centre-Tapped Resistor with Two Resistors

I have just started research and design on a small tube guitar amp and have hit the first of what is probably many uncertainties. The idea is to reuse the transformers, 7C5 power tube and 7Y4 ...
slubtle's user avatar
1 vote
1 answer
99 views

Dropping the line voltage on an HH Scott 265A tube amplifier

I have a pair of monoblock tube amplifiers that were designed to run on 117VAC. My wall voltage is about 121-123V. What is the best way to drop the voltage down to an appropriate level? Option 1: ...
Jon's user avatar
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Reverse Transformer For Smooth High Voltage

So I want to make a valve audio preamp, but need a way to generate clean high voltage DC for the plates of my tubes. I started with rolling my own boost converter which worked well, but was unable to ...
G Frank's user avatar
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3 answers
96 views

Vacuum tube circuit behavior

I’m the following picture, how does the circuit work between points A and B? I’m confused about the polarity of the cathode in front of the heater element. Is the cathode positive? Image source: The ...
notaorb's user avatar
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6 votes
1 answer
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Understanding How this Phantastron Circuit Works

I'm having a hard time gaining an intuitive understanding of, and modeling with an equation, this particular circuit linked below. It's called a "Phantastron", and it was used in old radar ...
Matthias Birkemeier's user avatar
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Troubleshooting thermionic emission

I am attempting to make an electron beam device work. The setup is very basic - a wehnelt in a vacuum chamber connected to an AC filament heater source and a DC high voltage source as pictured below. ...
Magemathician's user avatar
1 vote
1 answer
161 views

X-ray filament and cathode connection

I was studying how X-ray machines works. I have seen that the filament creates a current that produces electrons. By applying a high voltage between the cathode and anode, the electrons move towards ...
kam1212's user avatar
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3 votes
3 answers
1k views

Is it possible to make cathode ray or electron gun without a vacuum?

I stumbled upon this picture on the internet here is the link https://www.reddit.com/r/ElectroBOOM/comments/16azeq5/cathode_ray_succesfully_shooting_a_plasma_beam_in/ I wasn't able to get info from ...
Majd's user avatar
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1 answer
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What kind of signal is at the grid of the triode in a VTTC?

Ok, so Adrian Marsh shows on his YouTube channel a VTTC with fractal fern discharges: https://www.youtube.com/watch?v=Oo_mINYLqOI It turns out to be a class C Armstrong oscillator, and Adrian has a ...
Hermolaou's user avatar
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2 answers
108 views

How were high voltage vacuum triodes used in TVs?

How were the grids of TV high voltage (over 10 kilovolt) vacuum triodes operated back in the day?
Hermolaou's user avatar
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1 answer
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Can a CRT last 100,000 hours or even 300,000?

Online, I could find that high-quality cathode-ray-tube displays (whether be it for a computer monitor or a television set) have a design lifespan of 30,000-50,000 hours of cumulative operation. I ...
CoastCity Lapse 00crashtest's user avatar
2 votes
1 answer
370 views

How much are OT100 tubes worth and what was their specific purpose?

I got this tubes OT100 and I want to know their value, and what are they used for. They are NOS, unused and in working state.
Mihai Gabriel's user avatar
3 votes
2 answers
205 views

Why need voltage doubler when transformer can be made for full voltage

I have seen old vintage tube power supply (for example Heath HP-23A), that transformer secondary is roughly 300v RMS and a voltage doubler is used at output to obtain 750+ V DC for vacuum tube anode. ...
Ashok Das's user avatar
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0 answers
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PWM with IN-12 nixie tubes [duplicate]

I have some IN-12 nixie tubes and I can drive them using TPIC6B595N chip which has 50V clamping. And this chip has G pin which it is possible to use global dimming. What I questioned is which PWM ...
enis's user avatar
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4 votes
1 answer
602 views

Tube guitar amplifier design

In the preamp section of the Soldano Slo 100 amplifier (schematic), the gain stages are capacitor coupled to each other and between the stages most of the input is fed to ground via RC circuits. The ...
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2 votes
2 answers
455 views

Hybrid tube-solid state amplifier

In a hybrid tube-transistor amplifier (tube front end and solid state follower stage) how is the rail voltage applied? Tubes and transistors have different collector/plate voltages. What is the best ...
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8 votes
1 answer
682 views

Review my guitar amplifier

I am building my first tube amplifier based on the following schematic (PDF): I designed a PCB: Both the schematic and PCB are available on github. Some things I considered: I added a switch for a ...
Besi's user avatar
  • 737
4 votes
1 answer
390 views

Help me make sense of this guitar amp relay circuit

Here is a channel-switching relay from a guitar amplifier. It is supplied with 6.3 V AC. Closing the switch (near center) operates the relay. It's on a schematic that's taped to my wall, and I started ...
Isaac Lubow's user avatar
1 vote
1 answer
1k views

Yet another 807 tube transmitter

I just can't seem to get away from these 807s. Although I am to the point where I might replace them with 6146s. I built this transmitter with a 6AG7 oscillator, and 2x 807 final amplifier. The ...
McMurdo's user avatar
  • 117
2 votes
2 answers
194 views

Can a vacuum triode switch large amounts of DC on and off quickly?

I need to switch an inductive load on and off very quickly. Turning an inductive load on and off very quickly implies the supply voltage is large, several kV. Peak current through the load is several ...
James Strieter's user avatar
3 votes
2 answers
248 views

Could a vacuum-tube diode be used to snub a relay's coil?

I recently asked a question about inductor flyback in relay computers on Retrocomputing.SE. The preferred modern way to snub the inductive kick of a relay's coil is to add a flyback diode across the ...
DrSheldon's user avatar
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0 answers
52 views

MNA matrix of a vacuum tube

I've been working on a project involving a digital model of a vacuum tube. We're currently experimenting with a Wave Digital Filter approach. Now I've been reading Kurt Wegner's fascinating work and I ...
João Vaz's user avatar
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0 answers
218 views

How to find the total gain for a particular gain stage

Can someone help me how to calculate the total voltage gain for this particular gain stage? As you can see, there are five resistors. They are R3, R4, R5, R6 and R7. R4(100k) is the load resistor and ...
SnoopyKid's user avatar
  • 215
2 votes
4 answers
954 views

Low-voltage vacuum tube amplifier design

Amateur radio HF frequency amplifiers using transistors commonly can be powered with around 12 to 14 VDC, or even lower voltages, for QRP transmitters. Tube amplifiers seem to require DC power ...
hotpaw2's user avatar
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2 votes
0 answers
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Tube AM transmitter question

I designed an AM tube transmitter based on a crystal oscillator. Can you please tell me if this would work, or what I could improve?
George Chita's user avatar
7 votes
3 answers
2k views

How did the vacuum tube computer technicians know when a tube had failed?

I have read that in vacuum tube computers, a tube would fail every couple of days. How did the technicians know that a tube had failed? Wouldn't a broken tube silently cause the calculations to ...
Andrey Bienkowski's user avatar
1 vote
1 answer
127 views

Puzzling mains-frequency interference at output of signal generator

The output from the 1940's-era modulated oscillator I'm restoring is being fouled by a 50Hz signal and I haven't been able to find the cause of it - so I'm far from being able to eliminate it. It's a ...
Simon Owen's user avatar
1 vote
1 answer
240 views

How can I recreate a triode plate characteristics graph using a matematical formula?

Vacuum tube data sheets often include a graph of plate current vs. plate voltage for various grid voltages. For example, this screenshot from the GE 12AX7 data sheet: I would like to create this same ...
Dave H.'s user avatar
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7 votes
4 answers
915 views

What specifically causes damage when a transformer-coupled valve amplifier has no load across the secondary coil?

I'm new to this forum, so be gentle! I'm an electronics and computer systems engineering student, and I always thoroughly enjoy audio circuits, especially examining older valve based designs (I play ...
AL270's user avatar
  • 73
4 votes
2 answers
1k views

Is it possible to use CRT tubes for audio amplification?

I was wondering if it's possible for me to use the tubes in an old CRT TV to build an audio amp (specifically a guitar amp). If not, would I be able to salvage something else (like an old radio) to ...
Daniel Oren-Ibarra's user avatar
1 vote
0 answers
106 views

What is this device? (from historical photo)

Anybody know what this might be? It's from an old photo with my grandfather as a teenager who went on to work on radar during the war and later for "His Masters Voice" repairing televisions. ...
Brad Robinson's user avatar
0 votes
1 answer
112 views

Powering nixie tube from negative voltage?

I've built a photomultiplier tube supply; it takes +100VDC from a boost converter, which then goes through an inverting (in the sense of postive->negative rather than DC->AC) charge pump to give ...
T.S's user avatar
  • 107
0 votes
1 answer
136 views

Tube amplifier with buzz

I built a tube (UK: valve) amplifier but it has one problem. When I turn it on, it starts buzzing at 150 Hz but only if I connect the audio output transformer. If I directly connect the speaker to the ...
George Chita's user avatar
14 votes
6 answers
3k views

How did people make oscillators before they had the triode?

I found on Wikipedia that: “In 1901, Reginald Fessenden demonstrated a direct-conversion heterodyne receiver or beat receiver as a method of making continuous wave radiotelegraphy signals audible. ...
Camion's user avatar
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14 votes
1 answer
2k views

Geometric symbols alongside input filter capacitors on 1960's amplifier schematic

Capacitors C1, C2 and C3 are accompanied on this schematic by a semicircle, square and triangle symbol respectively. I'd expect the meaning of unusual symbols to be explained on the same drawing; they ...
Simon Owen's user avatar
1 vote
1 answer
123 views

Beta decay as electron source in vacuum tubes?

I've been thinking about this for a few days now, would this even be possible? There is another question like this being asked but via the photoelectric effect utilizing lasers. What if we used a ...
Biatu's user avatar
  • 13
0 votes
2 answers
188 views

Why does the wattage on the back of a tube amplifier not match the rating?

When I look at the back plate of a 15 watt Fender blues junior amp (which is a tube amplifier, meaning it uses vacuum tubes) it says 150W. However, the amp is sold as a "15 watt" amp. Why is ...
Marco Prins's user avatar
1 vote
3 answers
229 views

Why is a secondary transformer winding for VT filament heater connected to rectified output? [duplicate]

Ok I know this is a pretty narrow question. I'm learning about vaccum tubes, and I think I have the basics down, but this particular setup is confusing me. See the attached picture. In the given ...
ibanix's user avatar
  • 13
2 votes
1 answer
284 views

How does this pentode power amplifier (old technology, 1960s) work?

This is a diagram of a pentode power amplifier: This amplifier is used to control an electro-pneumatic actuator. Let me describe it a little bit: the input voltage (the control signal) is V3 (-30V &...
Dat's user avatar
  • 449
0 votes
0 answers
204 views

Doubt about high voltage measurement from amp chassis to earth ground

I built a tube amp (Fender 5f1 replica) and it works perfectly with a 3 prong power cord plugged into a properly earth grounded outlet. Any voltage on chassis and practically no "hum". I did ...
Cristiano Sarmento's user avatar
0 votes
3 answers
332 views

Output transformer in guitar amp produces sounds, while none comes through to the speaker [closed]

I built a Fender 5f1 Champ imitation. I've taken care to start it up gradually (first with no tubes, then just the 5Y3, then the 12AX7, then the 6V6 with the speaker connected and finally connected a ...
user3209815's user avatar
0 votes
0 answers
155 views

I have a carvin v3m 50watt tube amp head, red plating/bias help

The amp has 4 el84 tubes and 4 12ax7 pre amp tubes, the amp lost about half of its volume and the power tubes are red plating, is there any thing other than the tubes that I should be looking out for ...
Joe Cortez's user avatar
0 votes
2 answers
616 views

Best diode for very high frequency (Vacuum?)

If we look at what's commercially available, the diodes with the highest maximum frequencies I can find are in the low GHz range, of the Schottky type. I can also find research papers detailing ...
John Hawthorne's user avatar
20 votes
5 answers
4k views

Why is this meter giving different readings depending on its orientation?

My newly-restored (re-capped) 1950s vacuum tube voltmeter is now operational...but there's one further issue. The meter gives correct readings when lying on its back, but when oriented vertically- as ...
Simon Owen's user avatar

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