[R-390] 6080 in place of 6802 - RMS ???

[Howard Rawls]

Hey Rodney, I used a diode to drop half the filament voltage on the 6ba6's
in my R-390A.........it worked so good I forgot it was in there......and
just recently changed it.....after over 20 years of trouble-free
service.Absolutely no problem with short tube filament life. Of course, if
you are after really really really loooonnnnnggg life, I guess it is a bad
idea, like the fellas say. ;-) .
Howard

----- Original Message -----
From: Rodney Bunt <rodney_bunt@yahoo.com>
To: Barry L. Ornitz <ornitz@tricon.net>; <r-390@mailman.qth.net>
Sent: Tuesday, January 08, 2002 8:09 PM
Subject: Re: [R-390] 6080 in place of 6802 - RMS ???


>
> Two 6080 tubes with series fillament would require 12.6v at 2.5A. If they
were connected to a 25v
> 25v heater circuit can take the extra 0.6A current.
>
> Rodney
> VK2KTZ
>
> --- "Barry L. Ornitz" <ornitz@tricon.net> wrote:
> > Rodney Bunt <rodney_bunt@yahoo.com> wrote:
> > > OR you could put a single Diode in series with the
> > > filaments if you have no aversion to "sand state" devices
> > > in your R-390 (NON A).
> >
> > The 6080's filament is rated for 6.3 volts at 2.5 amps
> > while the 6082 filament is rated at 26.5 volts at 0.6
> > amps.  Two 6080 tubes with the filaments connected in
> > series would require 12.6 volts to run the filaments - not
> > 24 to 28.
> >
> > Adding a single diode in series with the filaments will not
> > do the trick either.  For the umpteenth time, the RMS
> > voltage of half-wave rectified AC is 0.707 times the RMS of
> > the original waveform.  The misconception that adding a
> > diode in series will allow a 6 volt tube to run on 12 volts
> > appeared in several early tomes on the R-390 receivers and
> > sadly it still persists today.
> >
> > In the case Rodney suggests, the 6080 tubes would have over
> > 9.3 volts RMS on the filament of each tube leading to very
> > short life.
> >
> >            Dr. Barry L. Ornitz     WA4VZQ     ornitz@tricon.net