Glowing Tubes Not During Christmas!

[Mark S Graalman]

  On some transmitting tubes, the 3-500Z for instance the
plate material is coated with a material that provides
gettering action when the plate reaches a certain operating
temperature. Some plate color is required on these tubes
for this gettering action to take place. The 3-400, 3-500, 3-1000
4-400, 4-500, 4-1000 and others should be operated with a
dull red color in the plate center in order to insure proper
gettering within the tube.

Mark  WB8JKR


On Thu, 25 May 2000 06:31:00 -0400 "Harvey A. Kader"
<optom at ATTGLOBAL.NET> writes:
> Holden wrote:
>
> > Minor correction to Harvey's statement that NO tube plate should
> glow - not true! I quote from "the Radio Manual" by
> > George Sterling, 1928, page 283: "with transmitter in operation
> handling traffic and all adjustments properly made,
> > the tube plates should not heat beyond a cherry red."  This is for
> a pair of UV-204A tubes. Page 313: "note plate
> > temperature and if not over a cherry red increase plate potential
> to 1000 volts." This is in reference to a set of
> > 211 tubes, which are fairly popular among the audio set. Older
> books are replete with such observations of plate
> > color. Numerous old tubes are designed to have some color when
> operating normally, however the 6L6 isn't among them!
> > In normal audio operation, power output tubes will often idle at
> near their maximum power dissipation. This requires
> > careful attention to bias, screen, and plate voltages, and plate
> current. A 6L6 with all these values within mfr
> > ratings should not glow. In considering changing out tubes which
> do glow but shouldn't, verify that ALL power supply
> > voltages are correct before doing so lest the new ones go the way
> of the bad ones! A tube which glows but shouldn't
> > in spite of all voltages OK is probably drawing too much current,
> and is NG.
> > Howie WB2AWQ
> >
> > "Harvey A. Kader" wrote:
> >
> > > Hi Bob.
> > >
> > > Just a note to let you know that NO tube should have ANY
> glow(red or orange) on its plates. Such a glow
> > > indicates TOO MUCH current running through the plates(for
> example 80mA versus 40mA). Glowing tubes will self
> > > destruct sooner or later - the higher the excess current, and
> the more intense the glow, the faster the tube
> > > will destroy itself.
> > >
> > > Thermal runaway is an example of a condition which produces a
> very glowing tube.
> > >
> > > As far as Chinese tubes are concerned, the small signal tubes
> are great(I have had zero problems with them), and
> > > the quality of the output tubes is increasing( slowly).
> > >
> > > I hope that this helps.
> > >
> > > Regards.
> > >
> > > Harvey A. Kader
>
> Hi Howie.
>
> I would NOT believe everything I read in manuals or textbooks. They
> have many mistakes, or outdated information by the
> time the book is printed. Sometimes what is written as fact in a
> manual or book is nothing more than the author's
> opinion.
>
> I would NOT operate ANY tube to the point of glowing red plates. The
> heater of a tube is designed to glow red - not the
> plates.
>
> Think of an electric stove with heater elements. The heater elements
> are designed to glow red ONLY - NOT the stove
> itself!
>
> My experience shows that glowing red plates is BAD for ANY tube. If
> people want to run tubes to the point of glowing red
> plates, they do so at their own peril and risk(AND at their
> equipment's peril and risk!).
>
> Regards.
>
> Harvey A. Kader
>
> http://www.angelfire.com/on/vacuumtubes
> http://www.geocities.com/tubesforsound
>
>

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