[Boatanchors] Tube filaments

Fri Dec 4 09:58:44 EST 2009

Hi Alex,

You're quite right about the 26.  A lot of those were used.  It was 
another case of keeping the AC filament voltage low to fight hum.  I 
skipped the 26 to get to the heart of the original 5-volt question.

The car radio saga is long and involved, but I doubt they were really 
popular until they lost their appetite for dry batteries and the 
necessity for the driver to "ride gain."

Best regards,
Al

Alex Whitaker wrote:
> Al,
>  
> The first widely used AC tube was the UX-226, which was an AC version 
> of the '01A.  The type '24 and '27 tubes didn't come out until later 
> in 1928.  The '26 had a 1.5 volt filament that required 1 amp of 
> filament current. '26 tubes are used a lot in the early AC sets, like 
> those made by Atwater Kent, RCA, and others. 
>  
> Also, there were car radios being used before the advent of AVC.  The 
> early Motorola and Delco radios of 1929-1932 mostly didn't have AVC.  
> They also didn't have vibrator power supplies or rectifier tubes.  All 
> their B+ was derived from B batteries that rode in an installed 
> battery well that sat under the front floorboards.  Vibrator power 
> supplies weren't readily available until 1933-1934.....their 
> introduction, along with better tubes, caused the popularity of car 
> radios to really take off. 
>  
> 73,
>  
> Alex
> AA9XY
>
> --- On *Fri, 12/4/09, Al Klase /<al at ar88.net>/* wrote:
>
>
>     From: Al Klase <al at ar88.net>
>     Subject: Re: [Boatanchors] Tube filaments
>     To: "Boatanchors Group" <Boatanchors at mailman.qth.net>
>     Date: Friday, December 4, 2009, 12:00 AM
>
>     Dave,
>
>     5 volts was chosen for the original mass-produced tubes like the 201
>     because it was around number, and appropriate for extracting a
>     reasonable percentage of the available energy from a 6-volt wet-cell
>     battery.  (A filament rheostat was generally used to compensate for
>     sagging battery voltage, as well as to control gain.)  When AC
>     receivers
>     were introduced,  the voltage was halved to 2.5 volts for heater type
>     small signal tubes like 24A and 27 as well as filament type power
>     tubes
>     like 45 to help control hum.  You need a separate filament supply for
>     the rectifier because it sits at full B+, so it was just as easy to
>     stick with five volts.  So the receiving tube world was largely
>     2.5 and
>     5.0 until the advent of car radios, which, BTW, had to wait for the
>     development of AVC technology.  6.3 is the nominal voltage of a fully
>     charged three cell lead-acid battery.  The 6.3 volt tubes are designed
>     to tolerate the 7 volts present when the engine is running.  The car
>     radio also required the introduction of 6.3-volt heater-type
>     rectifiers
>     like the 84/6Z4 and 6X5 or cold-cathode rectifiers like 0Z4 because
>     there was only one filament supply.
>
>     Al
>
>     David Knepper wrote:
>     > Does anyone know why RCA, etc. chose 5 volts for their rectifier
>     tubes and
>     > 6.3 volts for their receiving tubes?
>     >
>     > Just curious.
>     >
>     > Thank you
>     >
>     > David Knepper, W3ST/W3CRA
>     > Publisher of the Collins Journal
>     > Secretary of the Collins Radio Association
>     > www.collinsra.com
>     > Join today
>     >
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>     -- 
>     Al Klase - N3FRQ
>     Jersey City, NJ
>     http://www.skywaves.ar88.net/
>
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-- 
Al Klase - N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/