[Boatanchors] Tube filaments

[Alex Whitaker]

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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