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
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."

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.

Hang on here. Do you know what 813s cost these days? Still only around $10
!!
I got two at a hamfest last week. Got them hooked up to a filament xfmr,
and let them cook for an hour. Boy are they sure beautiful sitting there
glowing in the dark. They seem to be saying to me, "Hey we've been waiting
for 60 years to get a chance to make some RF!"
I also have 2kv waiting. So next step is to jury rig them up and see if
they draw plate current, with a little bias control, before I commit to
putting them in a new homebrew amp.
Since I just finished an 8877 amp this winter I am a little cautious and
aprehensive about hamfest tubes, because when I first fired up the 8877 with
4kv I got just that - fire. Seems the "I think it is good" tube a guy gave
me actually had a grid-plate short. Took a couple weeks to clean up THAT
mess. Fun stuff.
Thanks for all the replies, OTs.

73

Rick K2XT

On Thu, 3 Apr 2008, Rick wrote:

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.

Hang on here. Do you know what 813s cost these days? Still only around $10
!!
I got two at a hamfest last week. Got them hooked up to a filament xfmr,
and let them cook for an hour. Boy are they sure beautiful sitting there
glowing in the dark. They seem to be saying to me, "Hey we've been waiting
for 60 years to get a chance to make some RF!"
I also have 2kv waiting. So next step is to jury rig them up and see if
they draw plate current, with a little bias control, before I commit to
putting them in a new homebrew amp.
Since I just finished an 8877 amp this winter I am a little cautious and
aprehensive about hamfest tubes, because when I first fired up the 8877 with
4kv I got just that - fire.

Fuses in primaries and secondaries of plate transformers are your friends.

Variacs feeding the primary of the plate transformer (and with an ammeter)
is a good idea if you start out with low voltage on the primary, and pay
very close attention to all of your meters.

It is better to have more meters than not enough meters.

Sometimes an ohmmeter check on pins of tubes, BEFORE you do the smoke
test, is wise (I have done smoke tests where I got smoke, too).

Seems the "I think it is good" tube a guy gave
me actually had a grid-plate short.

I have had the experience, at hamfests, where, after money goes to the guy
and the thing goes to me, then he tells me "Oh, by the way,..(fill in
the blank)...."

Took a couple weeks to clean up THAT
mess. Fun stuff.
Thanks for all the replies, OTs.

After deciding to build a linear, the decision came down to the 813 for
the following reasons:

1. Large glass tubes need no special socket or chimney.
2. Tube manual says no forced-air cooling is needed.
3. Sockets are cheap. Plate capes are cheap.
4. Tube is cheap.
5. Filament cathodes are "instant on" whereas heater cathodes need warm-up
time.
6. Large tubes generally mean old-fashioned large grids and that means a
larger margin for error (i.e. overloaded grid dissipation) than those new
small sexy expensive small metal-ceramic tubes with dinky, flimsy, small
grids that vaporize if you accidentally overdrive them for more than 1-2
milliseconds (I've heard guys talk about this on the air).
7. I have no fan on my 2x813 G-G amp, and it is very nice and quiet
(unlike three other commercial linears I've had with objectionable fan noise).

Pictures of some of my stuff at: http://w4pon.freeshell.org
Not all that pretty but it all works and I know how to fix it because I
built it.

73

Rick K2XT

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."

A wrote:

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"?

On the 813, I don't know. But Eimac used to have a little handout on
filament regulation of their planar grid tubes; it talked both about
small static increases in current severely shortening lifetime as well
as inrush current issues. It's worth looking up and is probably on the
Eimac website.

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)?

I usually lose filaments before I lose emission on power tubes, but I
tend to run well below rated power. If I were running at rated power,
I might feel very differently.

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).

This is probably the result of a manufacturing defect in the filament,
and inrush-current limiting may not have done much good anyway there.

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."

Could well be... the sag due to charging the caps could well provide
effective soft startup. It might be worth measuring to see.

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?

I would suspect more people lose tubes due to bad emission than to filament
failures, but I also suspect people tend to be running finals hard out
there.

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.

Which factory did the Chinese one come from? I have had nothing but trouble
with Shugang products, but I don't know if the 813s are from Shugang or not.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."