Questions tagged [vacuum-tube]

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

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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 ...
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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 ...
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Is nine the maximum number of electrodes used in making thermionic valve/vacuum tube?

I was reading about vacuum tubes. In section called Multifunction and multisection tubes, they mentioned a device called a Pentagrid converter where I learned that vacuum tubes containing eight ...
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7 votes
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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 ...
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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 ...
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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. ...
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1 answer
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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 ...
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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 ...
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14 votes
5 answers
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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. ...
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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 ...
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Tube Amp Dummy Load With Headphone Jack - Distorted

I decided to make a dummy load / headphone converter for a tube amp. I did not expect it to be perfect, but the low end (~<500Hz) is very distorted. Amp Specs: 8 Ohm Output, 15W Max. So the circuit ...
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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 ...
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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 ...
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1 vote
3 answers
79 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 ...
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1 answer
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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 &...
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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 ...
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3 answers
125 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 ...
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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 ...
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2 answers
109 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 ...
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20 votes
5 answers
3k 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 ...
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102 views

600V DC Switch method question

I am making a linear PSU capable of O/P 600v @ 300mA. This is for vacuum tube experiments. I need to connect/disconnect the load from the PSU using a switch. I will not turn OFF the PSU itself. I ...
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Designing a hybrid RF ampilifier with tube and transistors

I have an 807 vacuum tube and I want to design a RF power amplifier with it. Since I have only one tube so I want to use transistors for the rest of the power amplifier circuit. The 807 tube will be ...
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1 answer
211 views

Strange ringing/oscillation in guitar tube amp

So I finally finished building my guitar amp. It sounds great, except for one thing that occurs when gain is too high. What happens is that when I turn one of the preamp volume pots high enough ...
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Restoration/mod of mid-1960s PP 2xEl844 4x6AT6 guitar amp, voltage, hum problems. Similar to Fender 5F10 schematic

Is this the right place to find solutions to the above problems? I'm trying to make this amp usable, but after some rebuilding and reconfiguring, I still have a hum problem and what seems to be odd ...
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Drive an older VFD tube via an Arduino et. al

I have a beautiful old itron DP95A4 tube that I would like to use as a small display to visualize some data. I suppose I'd need a driver and some sort of multiplexer, preferably used with an Arduino ...
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Vacuum tube DC amplifier circuit

I am currently working on a project to amplify a very small signal (about 10 millivolts) using a vacuum tube. I understand vacuum tubes were used as amplifiers and transistors back in the day, but I ...
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2 votes
0 answers
51 views

Vacuum tube emission (anode current, transconductance) percentage that is considered GOOD

Russian vacuum tube datasheets almost always specifies anode current like Ia = 100 mA +/-20mA at some conditions. The same with transconductance. But western tube datasheets specifies only one ...
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2 votes
1 answer
82 views

Tube amplifier preamplifier

I received this little two tube preamp http://www.gikfun.com/electronic-diy-kits-c-7/6j1-tube-preamplifier-board-20-stereo-multiple-diy-kit-p-730.html It comes with 9 470uF caps. The symbol on the ...
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3 votes
1 answer
207 views

Can you cover tubes?

All of the tube amp designs i see have the tubes exposed to air. Is this a design feature for heat dissipation or is it simply because some find it pretty?
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2 votes
1 answer
401 views

Powering 6E1P vacuum tube VU meter

This will probably be a rather lengthy and detailed question(s). I wanted to break things up, but since everything is kind of related, I've decided to keep it as one post. I do apologize if that's not ...
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Replacing X-ray or any radiation generating vacuum tubes with solid-state alternatives? [duplicate]

What are the reasons X-ray vacuum tubes could not be replaced by solid state alternatives? I'm thinking if it is possible to make a compact solid-state X-ray or higher energy photons generator just ...
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1 answer
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Which ground plane shape is more appropriate in my application?

I've been working on re-making the two PCBs in the HP 211A square-wave generator from 1955, as the traces on the one I own are starting to peel off. Focusing on one board, the multivibrator, for the ...
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3 votes
5 answers
1k views

Can a lower voltage overheat a magnetron?

Background I am working on a microwave oven that starts to emit an odor after 2 minutes of full heating despite otherwise working correctly. The smell is the same as that "sweet", ...
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2 answers
203 views

Why does triode voltage drop change as a function of grid voltage?

Imagine a thermionic diode connected in series with a resistor \$R\$. The circuit is hooked up to a voltage source \$V\$. The diode conducts a certain current \$I\$ and \$\Delta V_\text{diode}\ + \...
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1 vote
1 answer
324 views

What Causes Voltage Drop In A Vacuum Tube Diode

This question is about the voltage drop across a vacuum tube diode. Consider a circuit that consists of a battery, a vacuum tube diode, and a resistor all wired in series. My understanding is that, at ...
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2 votes
3 answers
248 views

Why most particle accelerators used vacuum diodes instead of transistors?

HERMES III (High Energy Radiaton Megavolt Electron Source) at the Sandia at Sandia National Laboratories is the world's most powerful gamma ray generator. HERMES-III produces a highly energetic beam ...
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6 votes
3 answers
319 views

Amplifiers without vacuum tubes or transistors?

Are there amplifiers that can work without vacuum tubes or transistors? Is it possible to create a working amp with high power without vacuum tubes or transistors?
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1 answer
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Photo-multiplier Tube Pin Configuration

Pin configuration of a photo-multiplier tube (PMT) is presented in its manual as can be seen in the attached image. All dynodes have been related to specified pins (numbered circles in the image) ...
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2 votes
2 answers
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Biasing network for phototubes and photomultipliers

I have some doubts about typical biasing network for vacuum phototubes and photomultipliers. Precisely, let's start by a simple photocathode. I have seen some biasing network like this one: In this ...
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1 vote
0 answers
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Guitar Amp Power Supply Issues

I have a B-52 AT100 guitar amp on my bench (naturally, it wouldn't let me attach the .pdf I have of the schematic, so I had to attach it as two .jpegs. The schematic can easily be found online though, ...
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14 votes
1 answer
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Why is there a winding on a capacitor?

I just came across this tube RIAA preamp on which there is a coil on the input capacitor, can someone please explain what's the reason of such thing? The schematic and the actual circuit bellow. The ...
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4 votes
1 answer
2k views

Insane power dissipation on EL34 tubes in push-pull power stage

Here's my circuit: (now without voltages) It uses two EL34s biased to -30V (fixed bias). Here's the loadline (made with this calculator): When no signal is applied voltage on EL34 anodes is 360V, as ...
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How to detect if vacuum tube is overdriven?

I want to somehow indicate(with LED diode for example) to user when vacuum tube is overdriven (When grid voltage is greater or equal than cathode voltage). My first idea was to connect a LED diode ...
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1 vote
3 answers
314 views

Plate current use of 12Ax7 vacuum tube at low voltage

Does anyone know the current used by at 12Ax7 (or similar) vacuum tube when in normal (triode) operation using a plate voltage no more than 10VDC? I'm not considering the heater current (~300mA at 6....
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1 answer
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Headroom of cathodyne phase inverter (in vacuum tube amplifier)

I know that gain of cathodyne is almost 1, so if it's going to produce 12V peak output, it has to take 12V peak input. However, if the bias is set to something like (-)1-1.5V, then peak voltage of ...
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5 votes
4 answers
2k views

In a parallel plate capacitor, how does placing a metal in between the plates reduce the capacitance?

This source claims that putting a metal plate in between the capacitor plates greatly reduces the capacitance. How is this possible? Two equal capacitances in series decreases the capacitance by ...
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2 votes
3 answers
384 views

Lighting up old vacuum tubes and making them turn on/off

I know there were older posts about lighting up old vacuum tubes but I would also like to turn them on and off. I am a complete newbie with no real electronic experience here so please bear with me. ...
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5 votes
3 answers
554 views

Low power tube headphone amplifier design

I have never worked or even listened to tubes/valves before, so its about time I did. I wanted a simple design to work with being my first tube project, and have found this from diyaudioprojects.com: ...
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2 votes
0 answers
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Fuzzy digits when driving with TPIC6B595

I designed a schematic and PCB of a simple Nixie clock and I hope that someone will be able to explain what's happening. The problem is that when I'm driving the cathodes with TPIC6B595 shift ...
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How close can an output transformer be to a preamp tube?

Imagine a layout for a tube amplifier. The power transformer is on one side, and the output transformer, input jack, and preamp tubes are on the other side. (Take a look at the Soldano SLO for example)...
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