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RE: - Re: OLD Tubes/Coils (fwd) - filament power (fwd)
---------- Forwarded message ----------
Date: Mon, 3 Mar 1997 18:16:33 -0500
From: "Robert W. Stephens" <rwstephens-at-headwaters-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: RE: - Re: OLD Tubes/Coils (fwd) - filament power (fwd)
> Date: Sun, 2 Mar 1997 11:01:28 -0700 (MST)
> To: tesla-at-poodle.pupman-dot-com
> Subject: RE: - Re: OLD Tubes/Coils (fwd) - filament power (fwd)
> From: Tesla List <tesla-at-pupman-dot-com>
>
>
> ---------- Forwarded message ----------
> Date: Sun, 2 Mar 97 06:07:24 UT
> From: William Noble <William_B_Noble-at-msn-dot-com>
> To: Tesla List <mod1-at-pupman-dot-com>
> Subject: RE: - Re: OLD Tubes/Coils (fwd) - filament power
>
> you said:
> Under-run the filament somewhat
> (say 10%) - the life will be greatly increased
> (I believe filament life goes as the inverse of
> the =fifth power= of the voltage if I remember
> correctly [maybe only the =fourth= -- it's
> a big factor] )
> [Bill] According to the GE light bulb book, it's the 13th power for lamp
> filaments (life/rated life to rated volts/applied volts), I don't see why
> tubes should be different. That makes your case even stronger
>
>
While it is true that filaments can be made to last longer by
starting them off in life when they are new at about 5% undervoltage,
and then increasing the fil voltage later in life to restore
emission, you have to be scientific about it, and the actual reduced
filament voltage employed has to be determined by actual power output
tests. If you attempt to force
full power from the tube in a power tube that has a thoriated cathode
which is operated at too low an emission temperature, you can strip electrons
out of the surface of the cathode which will not be replaced. The tube becomes
permanently crippled.
Power tubes operated in Tesla coils are often driven hard, way past
their specs. Since TC operation is short duration, it will still
take a person's lifetime to accumulate any real hours on the tubes.
I would advise not operating the filaments of power tubes in such
service at *any* reduced value from their nominal rated voltage as
stated in the manufacturer's data sheet or tube manual.
rwstephens