[ARC5] 7V and 14V Tubes

[Richard Knoppow]

----- Original Message ----- 
From: "Robert Eleazer" <releazer at earthlink.net>
To: <arc5 at mailman.qth.net>
Sent: Monday, April 30, 2012 3:37 PM
Subject: [ARC5] 7V and 14V Tubes


> Actually the Loctal Tubes with 7V and 14V filaments were 
> indeed meant for 7V and 14V filament voltages.  They work 
> OKay on 6V and 12V but were meant for the 14V and 28V 
> voltages used in aircraft.  Of course, aircraft 
> applications typically used the filaments powered right 
> off the DC power buss while AC line operated radios used 
> them either in a string or ran them off of a transformer.
>
> And I recall seeing a tube spec sheet that said the 7V 
> filament tubes lasted longer that the 6V ones if used with 
> 6V filaments.  So 7V tubes were an "improved" 6V as well 
> as being more suitable for aircraft or vehicle use.
>
> Only recently I discovered there are some 5V filament 
> tubes around, too,  and I have no idea why....
>
> Wayne


      Well, the RCA tube handbook lists filament voltages 
for all of the Loktal tubes as either 6.3V or 12.6V with the 
same current as the octal equivalents. Most of the locktal 
types have identical characteristics to octal based tubes 
with the exception of interelectrode capacitance because the 
bases have less capacitance than the octal type. There were, 
however, some types which were unique to the Loktal base.
      Now, there _are_ some 7 volt tubes, for instance the 
7AU7.  This tube is identical to a 12AU7 but has controlled 
warm up heater with 11 second warm up time. I is a nine-pin 
miniature.
     Running tubes at less than rated heater voltage affects 
other characteristics since it lowers the emission and 
general tube performance.  Its a reasonable practice to 
increase life provided the designer understands the 
performance trade-offs that must be made.


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