[ARC5] No Doubt Dumb Tube Question

[hwhall at compuserve.com]

 Good question! I took a look at my RCA Receiving Tube manual and it says that directly heated cathodes normally require less heater power to operate but the indirectly heated ones are better at keeping AC line hum off the supply, enable closer spacing of cathode & plates for lower voltage drop, and enable greater design flexibility. Bet there is more to it and more interesting info as well, if I had more resources! 

Wayne
WB4OGM



-----Original Message-----
From: Robert Eleazer <releazer at earthlink.net>
To: arc5 <arc5 at mailman.qth.net>
Sent: Mon, Jun 17, 2013 10:12 am
Subject: [ARC5] No Doubt Dumb Tube Question

 
 
 
I am reading some in an early 50's USAF training manual, Radar Circuit Analysis,  
because it gives a good description of vacuum tube circuit basics.  What I saw  
there led me to dig out my Sylvania tube manual and look up some data. 
 
Last year I was rebuilding the ham-built power supply of a BC-348 and was  
surprised to find that the transformer HV went straight to the filament of the  
rectifier tube.  I had never thought about it until I had to wire a rectifier  
tube socket, but had assumed that such tubes (e.g., 5Y3) used indirectly heated  
cathodes. 
 
But now I see in the Sylvania book that there are not only rectifier tubes like  
the 5Y3 that use just a filament but also those like the 5V4GA and 5AR4 that use  
indirectly heated cathodes.  Furthermore, such tubes seem to still have the  
filament hooked to the cathode internally. 
 
So why do some rectifier tubes have indirectly heated cathodes and others do  
not? 
 
Thanks, 
 
Wayne   
 
     
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