[Boatanchors] LINE VOLTAGE, FILAMENT VOLTAGE and SANITY

[D C _Mac_ Macdonald]

Somewhere in the deep recesses of my mind, I seem to remember that it is possible that the potential difference between plate and indirectly heated cathode CAN be enough to "rip" the electrons off that cathode if the cathode isn't heated enough to supply the current being drawn.  As I mentioned, this is something I heard or read MANY years ago. MAYBE, this is behind the earlier quoted statement about the 4CX250B. 
 
* * * * * * * * * * * 
* 73 - Mac, K2GKK/5 * 
* (Since 30 Nov 53) * 
* k2gkk hotmail com * 
* Oklahoma City, OK * 
* USAF & FAA (Ret.) * 
* * * * * * * * * * * 
 

 
> From: 1oldlens1 at ix.netcom.com
> To: w2hx at w2hx.com; kzerocx at rap.midco.net; boatanchors at mailman.qth.net
> Date: Tue, 6 Jan 2015 19:48:55 -0800
> Subject: Re: [Boatanchors] LINE VOLTAGE, FILAMENT VOLTAGE and SANITY
> 
> 
> ----- Original Message ----- 
> From: "W2HX" <w2hx at w2hx.com>
> To: "Gary Peterson" <kzerocx at rap.midco.net>; 
> <boatanchors at mailman.qth.net>
> Sent: Tuesday, January 06, 2015 6:32 PM
> Subject: Re: [Boatanchors] LINE VOLTAGE, FILAMENT VOLTAGE 
> and SANITY
> 
> 
> >> Do not attempt this procedure with indirectly heated 
> >> cathodes, such as the venerable 4CX250B.
> >
> > For us noobies, could you explain why this procedure is 
> > inadvisable with indirectly heated cathodes?
> >
> > 73 Eugene W2HX
> >
>     I remember reading the same thing but can't remember 
> where or what the reason was. Its common to reduce filament 
> voltage on diodes used as detectors or especially in noise 
> limiters because it reduces the effect of contact potential. 
> I have also seen this spplied to amplfiers. Again, my memory 
> is not coming up with complete information but I think in 
> power amplfiers the filament can be damaged.
> 
> 
> --
> Richard Knoppow
> Los Angeles
> WB6KBL
> dickburk at ix.netcom.com