Night air bouncy-bouncy, so they turn it down.
Directional patterns play a part, as well.
By using multiple antennas, it’s possible for AM stations to direct their signals in different patterns. Because of the potential for interference, stations may have to change their directional patterns at night.
Switching from daytime to nighttime pattern would also cause the signal to change, as David Simmons described it, at the flip of a switch.
No, you’re all wrong. You can’t pick up AM stations at night, because that’s PM.
AM band is still a useful medium, or would be, if it weren’t for the thousands of electronic devices that interfere with good reception. Light dimmers, computer power supplies, flourescent lights, monitors, etc. ruin decent reception. Lack of decent programming, i.e. music has relegated AM to a sort of backwater, and the rise of pay-services and currently advertisement-free XM and Sirius seals the deal. But it’s still cool to listen to WSM on a big 1930’s console…
egads, I would not want a replica! Pre-war consoles are plentiful and cheap, though they need a fair amount of work to overhaul. Definitely better performance and sound quality though.
But where do you get a 6L6 vacuum tube when you need one?
Most non-clear channel AM stations do have separate antenna patterns for day and night operation. One typically sets a pattern that “pulls a null” in the direction of another established station on the same frequency. I knew of a station in Toledo, OH that had a nighttime pattern that pulled a null in the direction of Pensacola, FL without altering power; one problem with this was that there was a fairly well-defined poor reception line going SSW of the city; you could be driving on a road just south of the city that crossed this line and here a significant drop in signal at night over a stretch of, say, less than a mile.
The FCC takes antenna patterns seriously. You are required once a month to go to designated points in your broadcast area and make daytime field-strength measurements for each pattern (you are allowed to switch to the nighttime pattern during the day to make these measurements). If another station lodges a complaint, you must produce these records.
Skywave is the reason for the change in signal, and as many posters note this is because of ionosphere changes between day and night. Essentially, the ionized E-layer high in the atmosphere is always ready to act as a mirror for signals in the AM frequencey range, but in the daytime sunlight ionizes an additional D-layer much lower in the atmosphere, effectively blocking skywave.
Russia. Seriously
Strangely enough, vacuum tubes are the easiest part of the equation. The hobby (demand) is small, and the number of tubes manufactured was staggering. Russia (and others) do make some of the more expensive audio output tubes that are becoming scarce or expensive but they aren’t generally a factor for radios.
My Dad likely has some in the basement. He has a few hundred tubes from the minis back through to loctal base.
The 6L6 is a beam power audio amplifier and might be used in a consol radio. Although I suppose the same thing in a lower power version like the 6V6 might be more likely.
6L6 is used in few radios, no doubt. The problem is that certain audio gurus have latched onto certain ancient tubes as having superior sound for their homebrew stereos, particularly in Asia. Tube types 45 and 50 in particular. They were used as final audio outputs in some sets in push-pull, so restoring these sets can get kind of pricey. This is where Russia and other tube manufacturers come in, the EL34, 6L6, 6550 types are made today. But it is very unlikely that the other radio signal tubes will ever be manufactured again as there is little demand, so what is left is what we got.
Aficianados can talk themselves into almost anything.