Questions tagged [vacuum-tube]

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

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47 views

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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1answer
259 views

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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1answer
1k 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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31 views

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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2answers
61 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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1answer
58 views

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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3answers
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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3answers
110 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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2answers
164 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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65 views

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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70 views

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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4answers
2k views

Measuring voltage across 1 ohm resistor

This might be a very stupid question, but I can't seem to figure this out and I'm going nuts thinking about it. Assuming you are trying to adjust the fixed bias of a tetrode push pull pair in a tube ...
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1answer
343 views

Is there a chart that translates old tube symbol to the new tube symbol [closed]

Im looking for a chart that helps you translates the old tube symbol into the updated format.
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141 views

Magnetron Working Principle

I was reading this simple description of magnetron working principle. Can you explain me why when electrons go near the cavities, they start to resonate at microwave frequency? I do not see the link ...
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2answers
131 views

Fixing an old radio [closed]

I am trying to fix an old radio that my girlfriend just bought. It's from around 1964. I'm just a normal electrician and I am not used to fixing things like this. Radio model: Huldra 7-45 Skapmodell ...
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1answer
53 views

Calculating Capacitance / Rolloff Frequency for Across the Line RFI Supression

I’m in the process of restoring my first All American Five (AA5) tube radio – in this case, a GE Model 115 from the late 1940s. As I’m getting ready to order replacement capacitors for it, one of ...
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1answer
140 views

Heating vacuum tube filament via capacitor

As I understand vacuum tubes (like triode / pentode) usually are designed to be heated with certain current through the filament. And usually it is about low-voltage and comparatively high-current. E....
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2answers
285 views

Troubleshooting Hum in a Tube Guitar Amp

I have a Fender Deluxe Reverb Reissue guitar amplifier that hums whenever I turn on the reverb. It sounds like loud 60 cycle hum. The reverb effect is still applied, but is accompanied by the hum. ...
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1answer
411 views

Tube Transmitter Issues

I'm back working on my friend's 807 tube transmitter. I've had some previous posts on this and I'd like to thank all the people who responded for your help! I bought an oscilloscope and a dummy load ...
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2answers
115 views

Electrodes and number of pins in vacuum tubes

I am confused regarding the terminology 'diodes', 'triodes' etc and the number of pins in these elements. If a diode has a cathode, an anode, and a supplementary anode (the control grid or plate) and ...
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2answers
106 views

How to obtain 360vdc from 240vac for audio use without a transformer?

I'm in the process of creating a tube guitar amplifier with an output power of ~6w (fender vibrochamp AA764) which requires the use of 360-400vdc. How could I obtain such a voltage from mains without ...
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1answer
186 views

Why would a tube radio leave the 6.3V heater tap on the transformer disconnected?

I'm attempting to repair a Clarion C104 tube radio. I started the repair years ago, put it away, and now I'm giving it another attempt. When I started the repair, the transformer (Clarion part no. C80-...
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3answers
2k views

In a vacuum triode, what prevents the grid from acting as another anode?

A triode vacuum tube has three electrodes, namely an anode, a cathode and a control grid in between of those. Assuming that the filament is hot, current would readily flow from the cathode into the ...
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1answer
88 views

+/- 96 V transformer less power supply design

I know this is a dangerous practice, but obtaining a transformer to make a vacuum tube power supply in my country is prohibitively expensive. So i have to go for transformer less psu. I am just making ...
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1answer
209 views

tube amp - high power supply voltage ?! troubleshooting

So I started working with troubleshooting a channel imbalance on the schematic attached, 12ax7 + 6L6GC push pull. But the problem seems to be a bit different... My voltages seem to be a bit hot!! (a ...
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1answer
269 views

Triode Regenerative Receiver Circuit - room for improvement and possible errors

I've designed this radio circuit, it's made to work on the 80m and maybe 40m band. Regen is controlled using a pot in the tickler coil. Tube is ECF82, coil is air cored on a 30mm former. Will it be ...
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2answers
816 views

Tube transmitter tuning

I am trying to tune/tweak/repair this transmitter for a friend of mine. It is oscillating, and it has rf power on the antenna, but it just doesn't seem as "strong" as it should be. The diagram says ...
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1answer
91 views

Tube transmitter plate current meter question

Can I install the mA meter in this schematic directly in the circuit? This is the high voltage plate supply and there is RF on it. The diagram doesn't specify if there is any circuitry to adapt the ...
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2answers
310 views

3.5 MHz 2W AM vaccum tube transmitter [closed]

What do you think of my 80m band radio transmitter I designed? Originally I though about using an Armstrong oscillator, due to its simplicity and sine wavyness, but I heard that crystals are better, ...
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2answers
76 views

Phase splitters/inverters using valves with directly-heated cathodes

I'm building an audio amplifier using Raytheon 6418 valves and I'm struggling with the phase splitter. The 6418 has a directly-heated cathode and I'm wondering what limitations this might introduce. ...
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1answer
374 views

Little Bear T11 tube phono pre-amp VACUUM TUBE upgrading

I have a Little Bear T11 vacuum tube phonograph pre-amp. It has three Shuguang 6N2-J "Military Grade" vacuum tubes which I want to upgrade. The pre-amp also has a Chinese made 6z4-J Rectifier. The amp ...
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3answers
302 views

Coloured coating within CRT

I have noticed that a lot of CRTs have a coloured coating inside of them that would appear to have practical purpose other than maybe protecting the aquadag. Paints and plastics tend to be avoided in ...
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3answers
223 views

Vacuum tube stereo amplifiers with an odd number of tubes

While researching the world of vacuum tube audio amps, I noticed that many commercially available stereo amps have an odd number of tubes. Here's a random example. How can a decoupled stereo sound be ...
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1answer
245 views

Power transformer question in vacuum tube circuit

I am having trouble wrapping my brain around this power transformer circuit. I must be missing something very fundamental, so I apologize in advance for that. Can someone explain to me why the center ...
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0answers
167 views

Vacuum tube voltage regulator - capacitor on the output

I'm thinking about building a tube-based voltage regulator to provide the power for the screen grids of the output tubes. I have seen multiple designs of this and am currently thinking of doing it ...
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2answers
131 views

Diode on op-amp output to drive tube

I am working on a tube based guitar amplifier, and found an interesting schematic online. There is an op-amp that has diodes across a resistor in the feedback path. I understand what it makes the op-...
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2answers
280 views

Modify a 1629 magic eye tube circuit to a 6E5S tube?

I've an EICO 950B capacitance tester with me. It has an aging 1629 magic eye tube. I have a bunch of 6E5S tube with me. Can you guys guide me with the modification? I know the first step to this is ...
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3answers
256 views

Why do tube amplifiers have such (relatively) small reservior capacitors?

In learning about guitar amps, I've been studying the schematics for solid state and tube amplifiers, and I found a pattern that I've never seen an explanation for. If you consider any of the main ...
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4answers
2k views

Why put a step-down transformer after a vacuum tube in an a valve amplifier?

I'm researching valve amplifiers. I found this schematic for one: So the input is amplified by the first valve, and then the amplified signal is amplified again by the second valve, right? My ...
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218 views

Magic Eye Tuning Tube Variable Negative Voltage

I am thinking about several applications of magic eye tuning tubes as display pieces and had a question about their operation. I have attached a sample circuit from a datasheet for an EM84 tube. I ...
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1answer
184 views

Is it normal for the OC2 vacuum tubes to glow bright orange during operation & OA2 to flicker while running?

I just got this vintage Heathkit IO-10 oscilloscope from ebay. Just tried powering it up and it seems to be working fine. But I noticed that the OC2 tube seems to glow very bright orange and the OA2 ...
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2answers
484 views

Question on Use of Y2 Saftey Capacitor in AA5 Style Tube Radio

In a radio I am restoring, there is a 0.1 uF capacitor between B- and chassis, designated as C12. My thought process is that if this capacitor were to fail, I would not want B- shorted to chassis as ...
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4answers
2k views

valve tone control circuit build

Here I have built the following schematic but have encountered some problems. The treble was crackling and the bass was dropping out. I have somewhat fixed the treble issue with grounding the pots but ...
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2answers
444 views

Calculating current in an unknown transformer with multiple isolated secondaries

I have an old power transformer that I'm retrofitting into a new valve amplifier. Having measured the voltages on the secondaries when 230V is applied to the primary and got the following results: P: ...
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1answer
271 views

Amplify Raspberry Pi Zero W Audio with 60s Tube amplifier circuit

First of all, thank you for taking a look at my question. Electronics is not my field of expertise, and I have found myself a bit stuck. I have been restoring some old 50s and 60s tube amplified ...
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1answer
58 views

Calculating voltage, current, and impedance values on an old transformer

I'm working on an old valve amplifier, with the intention of reusing the transformers in a new project. I've used what I know of transformers to calculate the ratio of each winding the corresponding ...
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0answers
311 views

What is happening to this vacuum tube?

I’m trying to repair a 63 year old record player. Opening it up, all of the electronics have aged badly, except for the drive motor, which is basic enough that it operates properly. I know enough ...
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4answers
164 views

Help me trying to understand transistor and vacuum tubes? [closed]

Obviously I'm a newbie in electronics and I think I understood how transistors and previously, vacuum tubes work (as a electrical switch, I'm disregarding amplifying in this question). But for me is ...
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1answer
395 views

Tube power supply capacitors replacement

I'm building the following power supply (credits to Audio design guide): I would like to replace C5, C8 and C9 with 1000uF capacitors (with the same voltage rate). From my understanding these ...
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1answer
405 views

Need help reading a schematic, is this a 220k log b pot?

This is saying a 220k log b potentiometer for the tone pot VR8, correct? That is such an extremely odd value, but I don't see that sort of notation very often either and I wanted to make sure I'm not ...