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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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76 views

Help identifying a variable resistor's function

I have recently acquired a TC Electronics Tube Pilot guitar effect pedal. While exchanging the vacuum tube in it, I noticed that there was a 22k ohm variable resistor on the board. Can anybody tell ...
6
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2answers
115 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
44 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
83 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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1answer
33 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
71 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 ...
3
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3answers
94 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 ...
1
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3answers
95 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
116 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
50 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 ...
0
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1answer
48 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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1answer
73 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
155 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 ...
13
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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 ...
1
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0answers
87 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 ...
0
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1answer
71 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 ...
1
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2answers
176 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 ...
3
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3answers
631 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
158 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: ...
2
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1answer
156 views

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

Dear Electronic Goorus, 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 ...
0
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1answer
48 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 ...
1
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0answers
191 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
141 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 ...
1
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1answer
233 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 ...
4
votes
1answer
215 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 ...
6
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3answers
427 views

Which particular transistor types represent triode and pentode vacuum tubes best?

If you encounter an old text which uses tubes instead of transistors, and if you are not familiar with the tubes, which one of the transistor from the following transistor tree would you think of to ...
3
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2answers
336 views

MAX6966 a suitable sink driver for nixie tubes?

I recieved some IN-14 nixie tubes for Christmas, and was hoping to implement them in a project i have been considering for some time. The details are unimportant, except that each nixie tube should ...
6
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2answers
1k views

Tube cathode biasing with CCS

I'm unable to understand how the biasing of the 12AX7 Tube in the schematic below works. In particular, I can't understand how the LM334 can switch on, where does it find the required voltage to ...
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2answers
248 views

Method for inductance measurement of iron core vacuum tube audio output transformers

I am involved in the direct measurement of inductance of vacuum tube audio output transformers. Inductance levels vary from around 1 H to 50 H for the primary and down to just a few mH on the ...
0
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1answer
128 views

What type of resistor component is this?

I have an RCA Victor 35x tube radio and I need to know what type of resistor this is and what it's purpose is? There is some wire wrapped around the resistor and it's attached to the antenna. ...
5
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2answers
979 views

What do “cycles” in a capacitor mean?

I'm trying to replace some old leaky capacitors for this radio I'm working on and in the data sheet they have this rating of cycles for the large capacitors near the bottom of the sheet here: What ...
2
votes
2answers
228 views

Edison effect in vacuum

I was reading this page which says: What Edison discovered (and it was promptly dubbed the "Edison effect") was that electrical current doesn't need a wire to move through. It can travel right ...
5
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3answers
1k views

How to identifiy this “2222 063 90025” vintage capacitor?

I am restoring an old stereo valve amp and would like to test (and replace if needed) some components. I don't know the history of the amp, but it's made in New Zealand and looks to be from the 1960'...
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1answer
138 views

Can a vacuum tube Triode increase the voltage in a circuit above the voltage rating of the batteries in the circuit?

I guess this will take a little explanation. I have not mastered the "sketching" used on this website yet. The triode in question has one plate circuit connected to a 90 volt battery and the filament ...
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2answers
72 views

Can an audion tube amplify a pulsating direct current or must the current be converted first to an alternating current? [closed]

Can an audion tube use a pulsating direct current as input and magnify the signal from the electrons flowing from the filament without first converting it to AC current? The reason I ask is that : I ...
10
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4answers
2k views

When a AM radio wave reaches the antenna does the signal need to be in a closed circuit to be amplified?

This needs some explanation. In the diagrams of radio instructions I always see a single line from the antenna to the input for amplification. Let's use a vacuum tube amplifier as for example. There ...
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1answer
628 views

Vacuum Tube Tesla Coil (VTTC) schematic interpretation

I'm quite new to the Tesla Coil stuff and I want to build a VTTC form a GU-81 tube. I'm using schematics from this Instructable. I don't want to make anything I don't understand and although I ...
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0answers
172 views

Ascertaining Valve Part Numbers

Old valves (vacuum tubes) sometimes do not come in their original boxes. Sometimes the part numbers seem impossible to read. Is there an easy way to read an apparently illegible part number? Would UV ...
2
votes
3answers
784 views

Need help adding gain overdrive/control to my tube guitar amp design

I'm new to analog electronics, so bear with me. Consider my guitar amp design: What we have is a 12AX7 feeding into a cathode follower, going into a James tonestack, through another 12AX7 gain phase, ...
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0answers
591 views

Solid State Output Tube Driver for a SE guitar amp

I'm learning as I go once again. Consider this output stage segment from a guitar amplifier I physically built: The LND150 is an "depletion mode" MOSFET, whereas the IRF820 is a normal "enhacement ...
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1answer
526 views

Simple vacuum tube tester design

I recently acquired a bunch of vacuum tubes from ebay and I'm in the process of trying to design a simple tester to check the functionality. Below is what I'm currently thinking about: I managed to ...
3
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2answers
233 views

Why Triodes for high power tubes

The Pros and Cons of Triodes Vs Screen grid tubes like Pentodes and Tetrodes are well documented elsewhere.When it comes to low and medium power tubes both triodes and screen grid tubes are readily ...
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3answers
2k views

Triode - how come grid is “more negative” than cathode?

This is probably the most lame question of all the time here, but... I cannot understad grid-cathode "negative" polarization. For me, grid is always positive to the cathode. I mean, in practice, ...
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4answers
604 views

Tube Guitar amp Input Transformer Removal

for a few weeks I've been trying to remove the input transformer from my little 60's Magnatone amp. The schematic indicates a 1:3 step up input transformer, but from reading elsewhere on the internet ...
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1answer
147 views

Matching radio tubes - what is widelly accepted tolerance in parameters?

When matching radio tubes, most important parameters are anode current and transconductance. Is there widely accepted tolerance in parameter variation? I have read an article where tubes are ...
8
votes
3answers
2k views

Why are thermionic valve/tube heaters generally designed to be 6.3 V?

Why are the heaters generally 6.3 V (or multiples thereof)? Does it make for an easy transformer winding ratio when used in countries with 120 VAC or 240 VAC mains? They often pull quite ...
1
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1answer
302 views

Running vacuum tube without grid or bias voltage

First some context: I am considering building a decoration out of a old RF power vacuum tube (like a Eimec 3-400Z, Telefunken RS630,...) with direct heated tungsten filament. I plan to get a ...
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1answer
204 views

Are tubes used for high voltage/high power h-bridge circuits?

If so, when working with a load that involves voltages > 1kV and power levels well into the kilowatt range, which type of tube would be more useful: Triodes or Thyratrons? I saw a similar question ...
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2answers
117 views

Another question about Lighting up Vacuum Tubes

Hi Can anyone tell me if the 4-400 on my vacuum tube means 4 volts? & how do I tell what voltage the large RCA tube is as there are only RCA 105 written on it. I'm making them into lights & ...
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2answers
449 views

What is the purpose of resistor Ra in this simple vaccum tube voltage amplifier circuit?

Came across this in a book, there's a brief explanation of why there's said resistor in the circuit: " ... it should be obvious that if we apply an audio signal voltage to the grid (i.e., vary the ...