[Boatanchors] Tube filaments

Fri Dec 4 21:11:04 EST 2009

With the current fad of ham AM to studio quality response, DC is often used 
on the filaments in receivers and low level transmitter RF and audio stages.

I use regulated DC on the filaments of oscillator stages in several of the 
receivers and transmitters that I use often.

Carl
KM1H

----- Original Message ----- 
From: "Ed Berbari" <eberbari at indy.rr.com>
Cc: <boatanchors at mailman.qth.net>
Sent: Friday, December 04, 2009 8:46 PM
Subject: Re: [Boatanchors] Tube filaments

>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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>
>
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