813 warm up glow
 

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

813 warm up time
 

If you are firing up the tube for the first time in many years, let it bake
with full filament voltage for a few hours to allow the vacuum to stabilize
and degas.

After the initial baking session from then on a second after filament
voltage is applied, you can apply all voltages for transmit.

Chuck...K1KW


"Rick" wrote in message
...
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?

Rick K2XT

813 warm up time
 

If you are firing up the tube for the first time in many years, let it
bake
with full filament voltage for a few hours to allow the vacuum to
stabilize
and degas.

I have done that and all still appears well. Even found a 10 volt, 16 amp
transformer
in the junkbox. Before I commit to using these tubes in a HB amp I will see
if they pull
plate current, and use a grid bias supply to control current. I have a
variac to control
plate current.
Tnx

Rick K2XT

813 warm up time
 

RCA took out an ad in the 1942 Radio Handbook. This, of course, was a
wartime publication.

The title to the article is "How to make transmitting tubes last longer."
They state:

"Long life - not maximum output - is the keynote of transmitting tube
operation today in many services where, because of war restrictions, it may
prove difficult to replace tubes that wear out. For tube types using pure
tungston, a 5% decrease in filament voltage will dobule tube life... Care
should always be taken in starting up tungsten filaments. Never should the
filament current exceed, even momentarily, a value of more than 150% of
normal.

For types using thoriated-tungsten filaments and oxide coated filaments, the
filament may be operated on the low side - as much as 5% below normal
voltage if the loading is light. The filament voltage should be increased
gradually to maintain output. Toward the end of life, additional service
may be obtained by operating the filament above its rated voltage."

The 813 has a thoriated-tungsten filament.

73, Colin K7FM

813 warm up time
 

On Sat, 5 Apr 2008, COLIN LAMB wrote:

RCA took out an ad in the 1942 Radio Handbook. This, of course, was a
wartime publication.

The title to the article is "How to make transmitting tubes last longer."
They state:

"Long life - not maximum output - is the keynote of transmitting tube
operation today in many services where, because of war restrictions, it may
prove difficult to replace tubes that wear out. For tube types using pure
tungston, a 5% decrease in filament voltage will dobule tube life... Care
should always be taken in starting up tungsten filaments. Never should the
filament current exceed, even momentarily, a value of more than 150% of
normal.

For types using thoriated-tungsten filaments and oxide coated filaments, the
filament may be operated on the low side - as much as 5% below normal
voltage if the loading is light. The filament voltage should be increased
gradually to maintain output. Toward the end of life, additional service
may be obtained by operating the filament above its rated voltage."

The 813 has a thoriated-tungsten filament.

73, Colin K7FM


The key issue which is not discussed at all above is that you have to look
at _some_ sample population to see the effect of lower filament voltage on
increased filament life. The question I ask, again, is how many guys out
there with filament cathode power tubes have had filaments blow out
(compared, say, with decrease in power output, or internal shorts that
blow fuses) in some manner that one might hypothesize is due to filament
warmup being too fast. Remember, I had one 813 filament open up on me even
though I was going from zero to ten volts, slowly over about ten seconds,
and on a Chinese 813 about one year old. So, I conclude, on a sample size
of one, that a filament can blow even if you raise filament voltage
slowly. Oh, yes, I also slowly decrease filament voltage to zero, too,
when I shut down the station. And, I'll remind everyone that I've had lots
of amplifiers in my ham career, and with no inrush protection, and never
lost a filament. I'd still like to hear from others about this.

Regarding higher filament voltages, I remember as a kid that we had a TV
set where the picture tube cathode emission deteriorated after some years
of use thus causing a weak picture (white areas were gray, gray areas were
black) and they had these little filament voltage boosters that caused the
filament to heat up to hotter temperatures thust restoring cathode
emission for some unknown additional period of time (I think the voltage
boost was from 6.3 vac to maybe 7.5 or so) since a hotter filament should
burn out sooner. Interestingly, we were still using that TV, every night,
for another three years. Again, a sample population of one. However, the
picture brightness did come back to fully normal levels.

In my own goofing off, I have raised filament voltage on a 6.3 v
expendable tube up to 18 volts, over a period of about one minute, before
it blew out the filament. It got quite bright. I have had momentary
mistakes where I have put 12.6 volts on filaments of 6.3 volt tubes for
periods of 10-20 seconds (turning off when seeing the filament get
abnormally bright) with no apparent effect on tube lifetime. Sample size:
maybe 3-4 tubes.

I had, once long ago, a tube hi-fi amplifier on which I put a variac and
was somewhat surprised that I still got power output even with 85-90 vac
going in, and over prolonged periods of time (Down at 75-80 vac, audio
droped off and distortion came up).

Surely there are a few people out there who have done some actual
(experimental) playing around with their tubes and can tell some stories
instead of passing on technical rumors.

813 warm up time
 

My Collins KWM-2 uses a home brew power supply. Step start on filaments -
at correct voltage and no high voltage for 60 seconds. Same tubes in it for
30 years. I think the only two power amplifier tubes that failed were
dropped on the floor. Some amplifiers adjusted the filament voltage to be
correct and some were never measured.

I ran a 3 x 813 amp for years and never changed the tubes or even measured
the filament voltage. Just used a transformer with the rated voltage and
called it good. Unless the filament transformer has a current rating much
higher than the demands of the amplifier tubes, the surge will probably be
ok.

Incidently, the home brew equipment looks practical. I built a vfo using
the Collins 70H3. The problem with it is that it covers 1.5 to 3 MHz with
10 turns. That is 150 kHz per turn. Bad for a linear dial. I used a 8:1
reduction gear and a crystal controlled mixer to cover 5 to 6.5 MHz, then
limited use to 5 - 5.5 MHz. That was coupled in as the second vfo for my
Drake TR-5, so when I switch it in, the Drake digital dial displays the
frequency. Extremely stable. Oh, I converted it to solid state, also,
which is easy to do. There is one minor problem in that there are no stops
on the dial. Not a problem for me, but if some kid came in and started
twisting, he could break something. Oh well, you need to take some risks in
life.

73, Colin K7FM

813 warm up time
 

A wrote:

The key issue which is not discussed at all above is that you have to
look at _some_ sample population to see the effect of lower filament
voltage on increased filament life. The question I ask, again, is how
many guys out there with filament cathode power tubes have had filaments
blow out (compared, say, with decrease in power output, or internal
shorts that blow fuses) in some manner that one might hypothesize is due
to filament warmup being too fast.

If I understand your request, you would like us to abandon the advice of
the tube manufacturers, and instead use our own anecdotal accounts of
tube filament failures?

It is unlikely that any of us have run herd on as large a sample set of
tubes as the manufacturers did. Clearly the chance of filament failure
among transmitting tubes (or any tube for that matter) is pretty small.

If we switch our focus to incandescent lamps, an example of a tungsten
filament with which we all have large experience, we could perhaps
extrapolate that anecdotal experience to tubes in general.

If I eliminate the cases where I dropped, or thumped the lamp bulb (trouble
lamps), I cannot remember a case where a household tungsten filament lamp
has failed at other than turn on or turn off.... and since I have spend my
life living with others, I cannot say for certain that those cases where
I thought the bulb must have failed on turn off, weren't actually cases
where it failed at turn on for a house mate, and they didn't take the time
to replace the bulb, or feel the need to tell me about the failure.

If, however, we wish to ditch the anecdotal evidence, there is ample
statistical evidence, compiled by the lamp manufactures, to allow them
to come up with the following equation for tungsten filament lamp life:

[life at test V/life at rated V] = [rated V/test V] ^ 12

Using a 5% reduction in operating voltage, we get:

[life at test V/life at rated V] = [Vr/(Vr(1-0.5))] ^ 12

or,

[life at test V/life at rated V] = [1.05]^12 = 1.85

Which means by simply lowering the lamp's applied voltage by 5% we increase
its life by nearly 2 times!

Which fits very nicely with the wartime conservation recommendations made
by some of the tube manufacturers.

-Chuck Harris

813 warm up time
 

A wrote:

The key issue which is not discussed at all above is that you have to look
at _some_ sample population to see the effect of lower filament voltage on
increased filament life. The question I ask, again, is how many guys out
there with filament cathode power tubes have had filaments blow out
(compared, say, with decrease in power output, or internal shorts that
blow fuses) in some manner that one might hypothesize is due to filament
warmup being too fast. Remember, I had one 813 filament open up on me even
though I was going from zero to ten volts, slowly over about ten seconds,
and on a Chinese 813 about one year old. So, I conclude, on a sample size
of one, that a filament can blow even if you raise filament voltage
slowly. Oh, yes, I also slowly decrease filament voltage to zero, too,
when I shut down the station. And, I'll remind everyone that I've had lots
of amplifiers in my ham career, and with no inrush protection, and never
lost a filament. I'd still like to hear from others about this.

It depends entirely on the application and how the tube fails in that
application. But yes, Varian has done statistical analysis and there is
an Eimac white paper on filament voltages.

Regarding higher filament voltages, I remember as a kid that we had a TV
set where the picture tube cathode emission deteriorated after some years
of use thus causing a weak picture (white areas were gray, gray areas were
black) and they had these little filament voltage boosters that caused the
filament to heat up to hotter temperatures thust restoring cathode
emission for some unknown additional period of time (I think the voltage
boost was from 6.3 vac to maybe 7.5 or so) since a hotter filament should
burn out sooner. Interestingly, we were still using that TV, every night,
for another three years. Again, a sample population of one. However, the
picture brightness did come back to fully normal levels.

Yes, the picture tube brightners will get a little extra life out of a
CRT with poor emission. So will a "CRT Rejuvenator" which will throw
a large reverse voltage on there to blow debris off the cathode.

Surely there are a few people out there who have done some actual
(experimental) playing around with their tubes and can tell some stories
instead of passing on technical rumors.

I suggest getting the Eimac white paper. Or for small signal tubes, a
copy of "Subminiature Electron Tube Life Factors," an NTIA report authored
by some Raytheon folks.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

813 warm up time
 

Nice stories below. Credible. Thanks. I have a few comments below.

On Sun, 6 Apr 2008, COLIN LAMB wrote:

My Collins KWM-2 uses a home brew power supply. Step start on filaments -
at correct voltage and no high voltage for 60 seconds. Same tubes in it for
30 years. I think the only two power amplifier tubes that failed were
dropped on the floor. Some amplifiers adjusted the filament voltage to be
correct and some were never measured.

Out of many dozens of tubes in ham gear, I think I never lost one by any
failure mode. I found an old Halicrafters S-85 at a hamfest and bought it
out of nostalgia. Has original tubes (all marked Halicrafters).

Our B&W TV sets (when I was a kid), however, had maybe half a dozen tubes
go soft and needed replacing. I've bought a number of ac-dc AM/FM radios
with tubes at hamfests and still have original tubes and still work!
Vintage 1950s.

I ran a 3 x 813 amp for years and never changed the tubes or even measured
the filament voltage. Just used a transformer with the rated voltage and
called it good. Unless the filament transformer has a current rating much
higher than the demands of the amplifier tubes, the surge will probably be
ok.

Incidently, the home brew equipment looks practical. I built a vfo using
the Collins 70H3. The problem with it is that it covers 1.5 to 3 MHz with
10 turns. That is 150 kHz per turn. Bad for a linear dial.

Yeah, I know. So, I use gears and don't worry about more than couple kc
accuracy. I'm not a Digital readout freak.

I bought a couple of R-390 VFOs from Fair Radio Sales (Lima, Ohio). Out of
three I bought, two worked and they are something like 2.4 to 3.4 mHz, and
so 100 kc/turn (ten turns nominal, twelve turns real, and still linear,
they go actually up to 3.6 so can use directly on CW part of 80 meters).

I used a 8:1
reduction gear and a crystal controlled mixer to cover 5 to 6.5 MHz, then
limited use to 5 - 5.5 MHz. That was coupled in as the second vfo for my
Drake TR-5, so when I switch it in, the Drake digital dial displays the
frequency. Extremely stable. Oh, I converted it to solid state, also,
which is easy to do. There is one minor problem in that there are no stops
on the dial. Not a problem for me, but if some kid came in and started
twisting, he could break something. Oh well, you need to take some risks in
life.

make your own stops.

73
W4PON

73, Colin K7FM

813 warm up time
 

On Mon, 7 Apr 2008, Chuck Harris wrote:

A wrote:

The key issue which is not discussed at all above is that you have to look
at _some_ sample population to see the effect of lower filament voltage on
increased filament life. The question I ask, again, is how many guys out
there with filament cathode power tubes have had filaments blow out
(compared, say, with decrease in power output, or internal shorts that blow
fuses) in some manner that one might hypothesize is due to filament warmup
being too fast.

If I understand your request, you would like us to abandon the advice of
the tube manufacturers, and instead use our own anecdotal accounts of
tube filament failures?

Yes. The advice of tube manufacturers comes from experience with fairly
large populations of tubes and what is wrong with us all just actualy
talking about our own actual experience (like I did)?

It is unlikely that any of us have run herd on as large a sample set of
tubes as the manufacturers did.

But a lot of us old timer-types surely had--just like me--several
amplifiers running 2-3-4 tubes in parallele, and for years, and that
starts to add up to a population of 10-20 tubes (at least for me). Not
large, but enough.

Clearly the chance of filament failure
among transmitting tubes (or any tube for that matter) is pretty small.

As I've said before, "chance" is speculative. Out of all of my hamming and
SWLing, I have heard very little on guys turning on their amplifiers and
discovering a tube that didnt' light up. I've heard more stories of guys
smoking their little metal-ceramic forced-air cooled tubes from
overdriving their grids, or "pushing" tubes, or using sweep tubes (I've
had a couple from hamfests where there was hardly any emission left) that
were maybe not tuned up fast enough, or whatever.

If we switch our focus to incandescent lamps, an example of a tungsten
filament with which we all have large experience, we could perhaps
extrapolate that anecdotal experience to tubes in general.

If I eliminate the cases where I dropped, or thumped the lamp bulb (trouble
lamps), I cannot remember a case where a household tungsten filament lamp
has failed at other than turn on or turn off....

Agreed. I've had a few flicker a bit and then a few light turn-ons
later...poof and it goes out.

and since I have spend my
life living with others, I cannot say for certain that those cases where
I thought the bulb must have failed on turn off, weren't actually cases
where it failed at turn on for a house mate, and they didn't take the time
to replace the bulb, or feel the need to tell me about the failure.

If, however, we wish to ditch the anecdotal evidence, there is ample
statistical evidence, compiled by the lamp manufactures, to allow them
to come up with the following equation for tungsten filament lamp life:

[life at test V/life at rated V] = [rated V/test V] ^ 12

Using a 5% reduction in operating voltage, we get:

[life at test V/life at rated V] = [Vr/(Vr(1-0.5))] ^ 12

or,

[life at test V/life at rated V] = [1.05]^12 = 1.85

Which means by simply lowering the lamp's applied voltage by 5% we increase
its life by nearly 2 times!

Yes, and sometimes it is worth doing this. I'll bet that the long life
bulbs out there are made with a little more filament wire so the
temperature is maybe (also) 5% lower, too.

Which fits very nicely with the wartime conservation recommendations made
by some of the tube manufacturers.

Fine.

-Chuck Harris