15

The last mass-produced vacuum tube was the Cathode Ray Tube, Thankfully those are now going the way of the dodo, replaced with much more practical LCD or OLED displays. (Edit: it turns out the magnetron is still mass-produced, for microwave ovens. Although apparently semiconductor replacements already exist, and soon the magnetron will go the way of the CRT....


10

As far as I know, vacuum tubes are used in newly-manufactured radio equipment (as opposed to still-in-use old equipment) for one purpose: high-power amplifiers. The advantages of vacuum tubes in this application are essentially from the fact that the tube can be built as a large and sturdy device. Semiconductor devices may fail due to overheating which ...


9

Vacuum tubes are neither outdated nor less efficient. See https://spectrum.ieee.org/semiconductors/devices/the-quest-for-the-ultimate-vacuum-tube The above IEEE Spectrum article talks about a vacuum tube amplifier that is more efficient than any solid state amplifier. This is just one example of active research on vacuum tubes.


7

I'm sorry if this answer doesn't answer your literal questions – it's just that these questions aren't strictly answerable. 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. It is commonly known that antennas come in more shapes than ...


6

This looks like a JAN-CTL-5948A, found via images within the search results for "huge vacuum tube". According to the linked site (from which the picture is also taken): The primary application of this tube is in high power, high voltage radar modulators. The 5948A is capable of supplying 12 megawatt pulses in this service. The datasheet indicates that ...


5

There's one more reason vacuum tubes are still used in amateur radios: personal preference of the amateur building the radio. Speaking for myself, I understand what's going on inside a vacuum tube much more clearly and deeply than I do the internal physics of a transistor. Further, it's much more comfortable (for me) to think in terms of increasing voltage ...


3

800 volts is far more likely to burn you. Just doubling the voltage from 120 to 240 will quadruple the power heating your flesh. This is just basic Ohm's Law: [P=E*I] DC is one nasty customer: It is easy to get complacent after spending a youth and a career working with docile, harmless 5-24 volts DC, or well-behaved 100 - 240 V AC voltages because of ...


3

Are you sure that you are correct in the comments about your pin 2 and pin 7? (The conventional numbering for these tubes is as in your drawing, so conventionally pins 8 and 5). If you look very carefully or use an ohm meter you might find that your pin2 is actually the cathode and your pin8 is G1, as in your drawing of the 6L6. This would be more normal ...


3

It is a pleasure to follow your adventures with vacuum tubes. A number of references indicate that "triode-strapped pentodes" can be directly substituted in regenerative receiver circuits. In Sound Practices Issue 2 (Fall 1992), Herb Reichert of Eddy Electronic Inc. wrote in Triode Connected Pentodes, "The Williamson amp ... triode connected [push-pull ...


3

DISCLAIMER: I offer these results only as a possible solution. Completing this design may depend on many other factors, thermal and electrical, steady state and transient, component- and layout-dependent parasitics. This is the subject of, at least, sizeable chapters if not entire text books, which I will not reproduce here. Your mileage may vary. I entered ...


3

Inspection of figures 17.17 through 17.19 in the ARRL Handbook suggest that the components in your Pi network might need to be adjusted: Jim Tonne, W4ENE, wrote a utility called PIEL to calculate output tank values. A Pi-L network - a Pi network with an L-network extension - is frequently used to match a wider range of impedances than a Pi network alone can ...


3

An interesting question. Not sure I can properly answer it but I'll contribute what I know. AM modulation methods Changing the RF output tube plate voltage was a very common way of producing AM when I was learning about ham radio in the 1960s. It was usually achieved by using a modulation transformer driven by an audio amp of the same output power as the ...


2

Paraphrasing the Wikipedia entry for the magnetron, we learn that, ... a stream of electrons passes by the openings to metal cavity resonators and causes microwaves to oscillate within, similar to the way a whistle produces a tone when excited by an air stream blown past its opening. The resonant frequency is determined by the cavities' physical dimensions. ...


2

I once wondered if a microwave oven magnetron might make a good transmitter, for CW for EME. I took a spectrum analyser and antenna to the kitchen and microwaved a glass of water, and I saw... The most awful collection of strong tones, covering a large part of 2.4 to 2.5 GHz, all of them shifting up and down in frequency, rising and falling, as the water ...


2

If the diameter of the glass base (just above the metal mounting bracket) is approx 5 ", its a type 5948 or 5948A, If the diameter o the glass base( just above the metal mounting ring) is apprx 7", its a type 1247. Both tubes are pulse modulators for radar with built in hydrogen replenishment.So they are nothing more than a high power switch. The ...


2

Referring to the circuit diagram for this set www.nostalgickitscentral.com/heath/schematics/heathkit_schema_sb102.pdf The mic connector has 2 pins and the grounded body as the 3 connections. As you have guessed the 2 pins are mic input (measured at 0 volts) and PTT switch (measured 30 volts). Both return to the body of the connector. The PTT pin is ...


2

A 1N3409 is a 39 volt Zener, completely unusable in a crystal radio (unless you are sitting at the base of the broadcast tower. ;-) Historically, 1N34 germanium diodes have been used because of the low voltage drop and therefore high sensitivity. They are a dime a dozen, so you can afford to blow up a lot of them.


1

Many radios do include a preamp that amplifiers the RF signal coming from the antenna. However there are many issues to consider. A truly broad amplifier will not only amplifier the radio signal you want, it will also amplify noise and even other radio signals on other frequencies. Most preamps are therefore some what narrow in bandwidth and their tuning is ...


1

You can use the tuning circut of the regen and, to be exact, the regen stage as a VFO for your transciever! Couple it to the separator amp with a 100pF cap between separator grid and the to of VFO tuning circut. Keying can be achieved by the key turning a relay on, the relay's contacts being connected to separator's cathode resistor and ground with a cap in ...


1

First of all, a voltage of 800VDC can be very dangerous if you happen to be touching anything at ground potential. An 800V potential is REALLY eager to pass some current down to ground, compared to a 120V potential. Also, because of Ohm's Law, if you were to touch something at a potential 6.66 higher (800V against 120V), you will get 6.66 times the current ...


1

Zeiss, the first step in fixing any radio is usually to check the power supply levels. If the power supplies are wrong then nothing will work properly. I would do that first before doing anything else. Also, when the plate current goes up does one or both of the valves glow brighter and brighter ? These two things will give clues to the fault. The fact that ...


1

The creap could be a bad capacitor or the circuit is over loaded due to excessive voltage on the plate. This sounds systematic of a component failure and requiring component isolation and L-C meters. You could have any number of bad components. You should be using a VTVM however the main reason is the level of the reading, milli. Sounds simple but first ...


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