[ARC5] 7V and 14V Tubes

[Geoff]

Loktals are listed at 7 and 14V nominal in Sylvania listings and 6.3 and 
12.6 as acceptable. Sylvania was the developer.


----- Original Message ----- 
From: "Richard Knoppow" <1oldlens1 at ix.netcom.com>
To: "Robert Eleazer" <releazer at earthlink.net>; <arc5 at mailman.qth.net>
Sent: Monday, April 30, 2012 7:11 PM
Subject: Re: [ARC5] 7V and 14V Tubes


>
> ----- 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
>
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