[Boatanchors] Tube filaments

Fri Dec 4 20:46:58 EST 2009

I would like slightly change the direction of this discussion on tube 
filaments.  My background is in medical electronics and when I first got 
started in this field tube amplifiers for biophyscial measurements (ECG, 
EEG, etc) were still common.  A leading company was Electronics for Medicine 
(E for M, now defunct) and they used DC voltages for filament supplies.  It 
was their way to limit 60 Hz hum from interfering with these low level 
signals.  I always wondered why this practice was not used with receivers 
and other low level signal circuits.  Instead we are burdened with numerous 
bypass capacitors and other means to limit 60 Hz interference.  Any wisdom 
or thoughts out there on this approach?

Ed, W9EJB

----- Original Message ----- 
From: "Carl" <km1h at jeremy.mv.com>
To: "Alex Whitaker" <ehscott at sbcglobal.net>; "Al Klase" <al at ar88.net>
Cc: <boatanchors at mailman.qth.net>
Sent: Friday, December 04, 2009 9:43 AM
Subject: Re: [Boatanchors] Tube filaments

> The 32 Ford radio and some others used a dynamotor for the HV.
>
> The 32 Chevy had some sort of pre vibrator arrangement, forget what it was
> called.
>
> Carl
> KM1H
>
>
>
> ----- Original Message ----- 
> From: "Alex Whitaker" <ehscott at sbcglobal.net>
> To: "Al Klase" <al at ar88.net>
> Cc: <boatanchors at mailman.qth.net>
> Sent: Friday, December 04, 2009 9:17 AM
> Subject: Re: [Boatanchors] Tube filaments
>
>
> 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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