[R-390] 6080 in place of 6802

[Barry L. Ornitz]

Rodney Bunt <rodney_bunt@yahoo.com> wrote:
> 6080's can be used in place of 6082's in the R-390 
> (NON A), if you series the filament for both tubes....
> 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