[ARC5] 7V and 14V Tubes

[Geoff]

----- Original Message ----- 
From: "Richard Knoppow" <1oldlens1 at ix.netcom.com>
To: "Geoff" <geoffrey at jeremy.mv.com>; <kgordon2006 at frontier.com>; "J. 
Forster" <jfor at quikus.com>
Cc: <Arc5 at mailman.qth.net>
Sent: Tuesday, May 01, 2012 1:37 PM
Subject: Re: [ARC5] 7V and 14V Tubes


>
> ----- Original Message ----- 
> From: "Geoff" <geoffrey at jeremy.mv.com>
> To: <kgordon2006 at frontier.com>; "J. Forster" <jfor at quikus.com>
> Cc: <Arc5 at mailman.qth.net>
> Sent: Tuesday, May 01, 2012 10:10 AM
> Subject: Re: [ARC5] 7V and 14V Tubes
>
>
>>
>> ----- Original Message ----- 
>> From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
>> To: "J. Forster" <jfor at quikus.com>
>> Cc: <Arc5 at mailman.qth.net>
>> Sent: Monday, April 30, 2012 9:27 PM
>> Subject: Re: [ARC5] 7V and 14V Tubes
>>
>>
>>> On 30 Apr 2012 at 17:59, J. Forster wrote:
>>>
>>>> That logic explains the need for a separate transformer winding, but
>>>> not the 5 Volts.
>>>>
>>>> Having a few hundred volts between the heater and cathode of a tube
>>>> can lead to failures...  big time. Viz. the AC power supply for the
>>>> Cabadian WS19. A 6X4 failure often destroys the unobtanium power
>>>> transformer.
>>>
>>> I suggest that the 5 V tubes came about during the time that most tubes
>>> had
>>> 2.5 V filaments. 2.5 X 2 = 5.0.
>>>
>>> There is probably some historical reason for it, rather than a technical
>>> reason.
>>>
>>> Ludwell Sibley's book may tell us.
>>>
>>> Ken W7EKB
>>
>>
>> There is some consensus that 5V was the first voltage that allowed
>> sufficient emission and reliability resulting in the 1927 UX280 and
>> continuing sort of by habit until the 50's when a whole bunch of 6.3V
>> rectifiers arrived to support color TV, audio, industrial needs and even
>> then seperate transformer windings were common.  The 280 came out at the
>> same time as the 2.5V receiving tubes for the first AC operated sets.
>> Another reason for 5V was likely I*R losses involved in using a 2.5V type 
>> 80
>> and the combination of brittle transformer insulation as well as socket 
>> and
>> wiring.
>>
>> And, of course, a directly heated rectifier of any voltage required its 
>> own
>> winding.
>>
>
>     The voltages may have been chosen because early sets were run from 
> batteries.  The filaments may have been run from dry batteries but more 
> likely from wet cells of some sort. Also most early sets had some means of 
> adjusting filament current such as a variable resistor in series with 
> them.
>     I suppose some sort of authentic answers may exist buried deep in old 
> literature but one would need a lot of time to find them.
>
>
> --
> Richard Knoppow
> Los Angeles
> WB6KBL
> dickburk at ix.netcom.com


Far from likely since they were developed for RCA's first AC set, the 
Radiola 17. There was no provision for battery operation and if you wanted 
that buy the Radiola 16.
A bit later farm radios were developed to run off a 6V car battery or a 32V 
Wincharger type system.