[Boatanchors] LINE VOLTAGE, FILAMENT VOLTAGE and SANITY

[Richard Knoppow]

----- Original Message ----- 
From: "Jim Wilhite" <w5jo at brightok.net>
To: "Ray, W4BYG" <w4byg at att.net>; "Boatanchors QTH" 
<boatanchors at mailman.qth.net>
Sent: Tuesday, January 06, 2015 9:27 AM
Subject: Re: [Boatanchors] LINE VOLTAGE, FILAMENT VOLTAGE 
and SANITY


> Commercial service that broadcasts either 18 or 24 hours 
> per day, seven days per week is considered CCS.  Amateur 
> service is ICAS.  There is a world of difference.  The 
> Collins 30S1 is the only amplifier I ever saw with a 
> metering position for the tube filament and an easy way to 
> adjust it.  But then again, they targeted the military and 
> government service, only hams with a lot of money could 
> afford them.
>
> In CCS tube longevity translates to service life which 
> translates into dollars.  When restoring a piece of 60 
> years old tube equipment, you will replace far more 
> electrolytic capacitors than tubes.  If anyone looks at 
> our obsession with exact voltages, you will note it came 
> with the rise of digital voltmeters.  Sort of like the SSB 
> stations that operate on exact frequencies because of 
> digital frequency readouts.
>
> Jim
> W5JO
>
    The effect of filament voltage on tube life is covered 
in publications from Varian/Eimac. The greatest effect is on 
"bright" or pure tungsten filaments, used mostly in old type 
high power tubes but is also applicable to thoriated 
tungsten. Some care is needed because its important that the 
emission be sufficient. For tungsten filament tubes or lamps 
a relatively small reduction in voltage has a significant 
effect in extending life while a small increase in voltage 
will decrease life even faster.
    The publication also discusses the effect of cycling on 
and off of filaments. Generally, its recommended that tube 
filaments be left on unless the equipment is going to be off 
for quite long periods of time. Thus, a broadcast station 
that is off the air for several hours a night should leave 
the transmitter filaments on for longest life.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com