[ARC5] 7V and 14V Tubes

[Geoff]

----- Original Message ----- 
From: "Robert Eleazer" <releazer at earthlink.net>
To: <arc5 at mailman.qth.net>
Sent: Monday, April 30, 2012 6:37 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.


Not true until WW2. Loctals were used in auto radios starting in 1939 and 
then in versions of the AA5 where the 14 series and higher were used. The 
prewar battery portables also used a lot of Loktals (Sylvania trademark).

I remember in the late 50's working at an auto radio shop part time that 
loctals had more problems with pin contact than others and that tubes such 
as the 7C5 had the same failures as the 6V6....low emission and H-K leakage.




> 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....
>

Primarily because it was prudent to have the rectifier tubes on a seperate 
filament winding so that a short circuit or arc didnt take out the other 
tubes..
For vehicle use there were 6V rectifiers such as the 84/6Z4, 6X5, 6X4, 12X4.


> Wayne
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