Amateur Radio Stack Exchange
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Questions tagged [vacuum-tubes]

This tag is for questions relevant to vacuum tubes, also known as thermionic valves or simply valves.

Despite having gained the moniker "glow-FET", a vacuum tube is century-old technology in which electron flow is manipulated and controlled by grids, beam forming plates. The first vacuum diodes (rectifiers and detectors) appeared in 1907, and by 1914 they were widely used in radio, both commercial transmitters and high-end receivers. They figured heavily in science fiction as late as the 1960s, despite already beginning to be replaced by transistors for most applications.

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Why are vacuum tubes still used in amateur radios?

I wonder, even in this modern generation why the outdated vacuum tubes are used. In other electronic circuits they have been replaced by more efficient (and small) transistors years ago. Why they are still used?
Sumithran
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help identifying a vacuum tube

I recently bought this tube for use in an art project and would like to know what it is and what it was originally used for. Unfortunately, the silkscreen labelling on the glass envelope was worn off and unreadable and there are no other obvious…
niels nielsen
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Pentode vs. Triode in Tuned RF Reflex Receiver

I'm planning on building a multi-band vacuum tube receiver. I've got a circuit diagram in hand for a two triode twin reflex with optional regeneration (P.E. Edelman, Reflex Radio Receivers, 1924, Fig. 35, also discussed here), and expect to use…
Zeiss Ikon
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Heathkit SB-102 Plate Current out of control

I bought a "technician special" Heathkit SB-102 transceiver. Everything seems to work well until I attach a dummy load and try to go through the "initial tune up" procedure in the manual. At the point where I switch the "Mode" to "Tune", instead of…
Zeiss Ikon
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Can a regen receiver be used as a CW transceiver?

I've looked for a while, but I've never found a design like what I imagine: a single-tube (valve) regen CW transceiver (no cheating with a tube/valve that has two or more triodes/tetrodes/pentodes in a single envelope). The way I imagine this…
Zeiss Ikon
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Identification of valve

My favorite receiver used for 40 m AM broadcasts has a cracked valve, but the valve type normally printed on the glass has rubbed away. Can anyone tell me what the numbers for this valve are ? The radio is mid - late 40's, made in Australia and has…
Andrew
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Frequency Display for Old Tube Radio

I have a Hallicrafters S-120 1960s vintage vacuum tube receiver (an "All American Five" superhet with solid state rectifier replacing one of the "five" tubes). It works well, doesn't have excessive internal noise, and seems very sensitive (with the…
Zeiss Ikon
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Is it practical to use a magnetic amplifier as an AM modulator in a transmitter?

If I'm building a vacuum tube HF transmitter (say, 40 m band), obviously the simplest mode to build is CW; it's common to key the oscillator input to the final (in order to keep the oscillator running stably, minimizing chirp and drift). If I want…
Zeiss Ikon
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Pi Matching circut for tube PA - what values?

I am working on my 80m and 40m CW transmitter and ran into a problem: I need to match the high impedance of PL504 to 50ohm coax, a Pi match seems to be the best, but I don't know how to calculate the inductor - the calculators online give capacitor…
thegamebusterpl
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How is working on DC high voltages as in a tube radio different from 120VAC?

Suppose that I am familiar with the safety procedures for working on 20 A 120 VAC 60 Hz household lines. What should I be prepared for before working on high voltage DC circuits (say, 800 volts) as is commonly found on the anodes in tube…
Mike Waters
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How to identify this vacuum tube?

I have a vacuum tube and need help working out what it is. The numbers on the tube are APW 8047 it 4 pin and fits in a B4 socket. I wasn't able to find it with a Google search of the number. Are there any resources that let me look it up? All found…
mort win
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Will a "crystal set" work with an untuned RF amp stage?

In my ongoing process of building up to a homebrewed general coverage receiver/transceiver, a first step might reasonably be a crystal set, where a tuned circuit and simple, or even improvised, rectifier extract enough power from the transmitted…
Zeiss Ikon
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Has this regeneration control been done?

I'm planning to build a two-tube reflexed RF regen receiver soon. I'm examining methods of controlling the regeneration — it needs to be possible to both initiate and halt oscillation in all bands (I plan to cover 500 kHz to 30 MHz, if I can manage…
Zeiss Ikon
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What are the properties of the radiation of a magnetron?

It is commonly known that electromagnetic radiation from an antenna is polarized; the electric field is parallel to the rod and the magnetic component is perpendicular to it. What does the radiation of a magnetron look like? Is this radiation…
HolgerFiedler
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How to identify the mic connection pins in Heathkit SB-102?

One of the things I need to do to put my Heathkit SB-102 into service is connect a microphone. I've got a suitable crystal mic, with four conductors in the cable -- two for the mic element, and two for the Push To Talk (PTT) switch. The PTT switch…
Zeiss Ikon
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