[Milsurplus] Re: half-voltage dynos

[Bill Cromwell]

On Sun, 2006-12-03 at 08:53 -0500, William Donzelli wrote:
> > So half-volts on the fils will work, sorta.
> 
> It mostly depends on the tube and the maker. For the octals of the
> Command Set era, I doubt they would work. Later today I might see what
> the tube testers say, but from my experience, I would say no go. Too
> many times I have plugged a tube in, set it up, then grumbled when it
> showed DEAD, then noticed that I set the filament voltage switch
> wrong.
> 
> > I've run my RAT-1s at 28 volts B+ and they work well,
> > but I never tried half filament voltage.  I wonder about that.
> > When I get some time, I'm going to see if I can recreate
> > those conditions and measure just how well they work
> > at half-speed on the filaments.
> 
> It might be fun to see how it works, but do not leave it that way. The
> lives of most tubes is drastically shortened when filament voltage is
> dropped too low.
> 
> --
> Will
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Hi,

There are some low power receiver applications that run the filaments or
heaters "starved" -half voltage or less. They also run at very low plate
voltages - maybe 8 volts or so. The writers have not said anything about
tube life except that the tubes loafing along and should last "forever".
I am going to try it eventually.

There are different materials used for filaments and indirectly heated
cathodes. Some of those are very sensitive to reduced voltages and
especially when used at the full rated plate power. Some transmitting
tubes come to mind. I have some old surplus radios and I don't think the
tubes would be particularly sensitive to reduced heater/filament
voltages. Obviously they need enough heat to produce some emission. I
have limited personal experience with this and I won't be able to try it
in a timely manner for this thread. Apparently other people have
successfully done it beyond the extent proposed here.