5 Jun
2010
5 Jun
'10
4:42 p.m.
During the early years of WWII, many of the amateur
radio
publications ran ads from RCA that advised dropping the
heater/filament voltage on transmitting tubes by about 10% and
derating them somewhat. ?Apparently this could result in a doubling
of useful life.
No - it is ham lore only. Many tubes lives will shorten if the
filament is run below spec. In some types, life will drastically drop.
--
Will
5 Jun
5 Jun
5:05 p.m.
On 5 Jun 2010 at 19:42, William Donzelli wrote:
No - it is ham lore only. Many tubes lives will
shorten if the
filament is run below spec. In some types, life will drastically drop.
Okay, you made me go and get my 1942 "Radio Handbook".
In the back, with all of the ads, there is a 2-page spread from RCA
entitled "How to make transmitting tubes last longer". Number one on
the list is "Reduce filament voltage":
"For tube types using pure tungsten filaments, a reduction of only 5%
of the filament voltage doubles tube life. A reduction of 15%
increases it almost tenfold!..."
"For types using thoriated-tungsten filaments and oxide-coated
filaments, the filaments may be operated on the low side--as much as
5% below normal voltage--if the loading is light..."
Another scam perpetrated by "General" Sarnoff?
--Chuck
5:27 p.m.
In the back, with all of the ads, there is a 2-page
spread from RCA
entitled "How to make transmitting tubes last longer". ?Number one on
the list is "Reduce filament voltage":
"For tube types using pure tungsten filaments, a reduction of only 5%
of the filament voltage doubles tube life. ?A reduction of 15%
increases it almost tenfold!..."
"For types using thoriated-tungsten filaments and oxide-coated
filaments, the filaments may be operated on the low side--as much as
5% below normal voltage--if the loading is light..."
5 percent is generally the tolerance on the filaments anyway.
For thoriated filaments (and note the fishy language used - "low
side"?), anything over a 5 percent variation is bad news. Most of the
popular transmitting tubes of the mid/late 1930s were thoriated
tugsten (203, 211, 801, 805, 808, 838, 845, 860, many others).
--
Will
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