From dawsond–(at)–ostoffice.worldnet.att.net Mon Mar 23 13:10:39 CST 1998
Article: 60680 of rec.audio.tubes
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From: Douglas Dawson
Newsgroups: rec.audio.tubes,rec.antiques.radio+phono
Subject: Re: 6.3 V vs. 5 V heater
Date: Mon, 23 Mar 1998 07:59:17 -0800
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Here’s a few more points that no one has touched on yet:
1. The early AC tubes (types ’24 & ’27, but not type ’26) were 2.5 volt
heater types. The ’26, with its 1.5 volt filament, was a special AC
design which attempted to eliminate hum by mutual cancellation of the
effects of the electric and magnetic fields from the filament. This
required that the choice of filament voltage and current be “just right”
in order to get the cancellation effect.
2. The type ’80 has a 10 watt filament which would have required 4 amps
at 2.5 volts, probably a bit too much for the plug-in socket connection.
Therefore it probably seemed reasonable to double the “standard”
filament voltage to 5 volts in order to keep the current down to 2 amps.
3. The first 6.3 volt tubes, types ’36, ’37, ’38, etc. were developed
for use in automobile receivers when cars had 6 volt batteries. Some
radio manufacturers, notably Philco in the US, quickly adopted these for
mains-power radios as well. The rest changed over within a few years.
The result of these choices, as the earlier commenters have noted, was
to establish 5 volts as the “standard” for rectifiers and 6.3 volts for
other types.
Doug Dawson
Claude Frantz wrote:
>
> It has been a common practice to use a rectifier with a 5 V heater
> although the other tubes had 6.3 V heaters. In fact, rectifiers with
> a 6.3 V heater exist too. Using a rectifer with direct heating
> make it necessary to use a separate winding on the transformer, but
> why should the voltage be different ? Any explanation available ?
> —
> Claude
> (claud–(at)–auv106.bauv.unibw-muenchen.de)
> The opinions expressed above represent those of the writer
> and not necessarily those of her employer.
