The AM Forum

Happy Valentines Day to All and to our XYL's

FRED

Fred,

Actually, I think that is an old incandescent light bulb, but I get the message!

I wonder if Hallmark offers that card  with a 4-400A or an 833A on it instead; I'd like to get one for Janet for this coming Valentines Day.

When I go to the card store tomorrow, I'll let everyone know.

The audio guys can perhaps get Hallmark Valentines Day cards for their sweeties with 300Bs or KT-88s on them.

73,

Bruce

Looks like an Audion tube that was floating around in 1910.
The old style bulb shape.

Fred

I recall reading in Radio and Television News in the mid-50's that some outfit was launching a campaign urging TV repair shops to collect old carbon filament light bulbs with the little tit on the end of the glass envelope, because they tended to self-oscillate at VHF and cause TVI.  They promised to swap one-for-one a brand new (modern incandescent) bulb for every carbon filament one turned in, and indicated that all bulbs collected would be sent to a crusher, to assure that they never interfered with a boob tube ever again.

Of course, they didn't place much emphasis on the fact that those old carbon filament bulbs would often burn continuously for decades, and that some of the bulbs in question dated back to the turn of the 20th century, while a modern incandescent lamp even back then would last at most a few months.

I remember about 15-20 years ago some guy at Dayton was selling antique light bulbs, and those old carbon filament lamps, with good filaments, were going for $30 apiece.

http://www.centennialbulb.org/   8)

Don,

Very interesting. I would have had no idea that the older incandescent lamps either produced VHF oscillations, or exhibited the kind of operating lifetime as you have stated.

I must admit that you are one of the best sources (if not the best) for some of the most arcane and interesting trivia pertaining to older electronics technology.

Please, this is meant to be a compliment! Do not take it any other way. I for one very much enjoy reading this kind of thing, so please continue your best effort to post these snippets.

73,

Bruce

The explanation was that somehow the carbon filament may exhibit a negative resistance characteristic, and the way the filament is bundled up inside the envelope,  it may resonate at vhf, causing it to go into self-oscillation.

I have one of those old bulbs here, although I have never tried giving it a life test.  I did power it up once, and I'm sure it wouldn't win any Energy Star award.  At full voltage, the filament just gives off a warm orange glow, kind of like a tube filament.

I found a reference to the phenomenon here (http://books.google.com/books?id=Oy0DAAAAMBAJ&pg=PA228&lpg#v=onepage&q=&f=false), but I am not sure the writer gives the correct explanation of the phenomenon. Popular Science, November 1957, p. 228

the conspiracy theorists could have a heyday with the light bulbindustry.

Some kids with a pellet rifle tried to shoot that thing out from across the street.  They city about hung those idiots.


Clark

they should have been shot with the pellet rifle.