On Thu, 3 Apr 2008, Scott Dorsey wrote:

In article m,
A wrote:


On Tue, 1 Apr 2008, Rick wrote:

How long after applying filament voltage till the 813 is ready to transmit?
Is it like a 3-500 or do I have to wait 30 seconds or so?


When the glow is up to bright orange, then you are ready. If you apply the
filament voltage without "management" (i.e. a slow increase over, say 5-10
seconds), the tube should be ready for transmit in, like, about 1-2
seconds. In a heater cathode (rather than a filament cathode), you need to
wait for that thin "coat" to come up to a dull orange and that can be half
a minute or so depending on the tube.

Note that slow turn-on will radically increase the lifetime of these tubes

1. I recall a research topic handout mentioned in a QST from maybe 2
decades ago that said this but did not give actual numbers. Does anyone
have something specific in terms of what they call "radical"?

2. I also recall relatively little _actual_ discussion, from my SWLing
days on the ham bands 50 years ago, of people complaining about blowing
out their filaments sooner than they would be happy about, so do any of
you guys have any real life experience with this (instead of passing on
"conventional wisdom" that has been passed on as conventional wisdom by
everyone else that passes on conventional wisdom)?

3. Usually tube/filament lifetime is something like "insurance"
statistics. There will be an "S"-shaped curve with some characteristics
and this means a lot of filament lifetime experience will only show up in
fairly large populations.

4. For the record, I bought, some years ago, three Chinese 813s, brand
new, and after six months, one of two of them blew a filament (I barely
noticed it since at the end of the QSO I noticed my plate current was
running half of what is should have been) in my pair-813 linear (with
variac on the filament transformer).

5. Inrush currents will often be, already, limited to some degree because
filament cold resistance will be lower than hot resistance and most of the
secondary voltage will appear across secondary resistance which will be
almost identical either warm or cold. For power transformer powered
linears (etc), the HV is dumping into a string of electrolytics thus
building in, perhaps, 100-200 (?) milliseconds of "delayed" or "limited"
inrush current because that part of the transformer is
temporarily "overloaded."

6. How many of you guys with 3-500Z and 811 amplifiers (572-Bs, 4-X, etc,
and there are a lot out there) are replacing one or more of your tubes every
year or two because one or more filaments won't light up the next time you
turn on your rig? How many of you guys have the same tubes in your
amplifiers for a decade or more and the filaments are still lighting up
just fine and RF output (and not on "pushed" tubes, either) is also just
fine?

Guys, how about some extended discussion on this? And, I've had a few of
all of these tubes at one time or the other almost since the beginning of
my haming before 1960 and never lost a filament till the Chinese 813.

P.S. The Chinese 813 had crappy soldering work on the pins at the bottom
of the tube, too. The other Chinese 813 is still running fine. I have some
Chinese 811s, too, and their pins are better soldered. Russkie 811s look
and work fine, too. I replaced the burned out 813 with a used 813 from a
hamfest (an old brand I forgot) but it has a darker "tinge" inside, but
the RF amps out are just fine.


if you're using them below full power level. An inrush current limiter
in series with the filament only costs a dollar or two and can easily pay
for itself a hundred times over.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."