[Amps] General question on filament life

Sun Feb 11 16:46:59 EST 2007

Hi,
not much experience of this, however I once worked for a lamp manufacturer, 
there was a tendency for lamps to fail at switch on ( I believe we have all 
seen this).
The cold resistance of a typical tungsten filament is roughly 14 times lower 
than the running resistance so if the supply impedance is low the inrush 
current is in the region of 14 times higher than the running current. I 
think the failure mechanism is related to the uneven rate of temperature 
rise whereby some parts of the filament briefly run much hotter than normal 
as some other parts are still warming up. I believe I have seen this in 
tubes/valves whereby sometimes the filaments go quite bright on switch on 
and subsequently appear to go dimmer.

With the life testing of lamps it was acknowledged that lamps that failed on 
switch on had little life left anyway, I believe the life testing schedule 
called for one interruption to the power source for 30 mins each day to 
simulate a reasonably realistic situation.

Currently I still maintain a radio scheme which runs multiple single 4CX250B 
transmitters (quasi-synch AM scheme), these transmitters have plate and 
screen modulation with an HT of 1400v. Most of these PAs are run at roughly 
70w carrier and have a surprisingly long life, each standby transmitter is 
permanently powered.
Bizzarely these standby transmitters also seem to have a good life despite 
the heaters running 24/7 with no anode current.

What seems to trash the valves quickest is the odd site where the screen 
voltage is reduced to reduce the power output, some of these when run at a 
carrier output of 10w will destroy the valves in maybe 2 years or so. Some 
of the transmitters running at the higher power level have run 24/7 for 
nearly a decade on one valve.
FWIW the filament supplies in these are regulated DC.

Regards David G0FVT

----- Original Message ----- 
From: <amps-request at contesting.com>
To: <amps at contesting.com>
Sent: Friday, February 09, 2007 5:00 PM
Subject: Amps Digest, Vol 50, Issue 25

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>   1. Re: 3-500z - intermittent filament (Robert B. Bonner)
>   2. Re: 3-500z - intermittent filament (Mike McCarthy, W1NR)
>   3. test - sorry (Larry)
>   4. Re: General question on filament life (Larry)
>   5. Re: test - sorry (Administrator)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Fri, 9 Feb 2007 08:28:55 -0600
> From: "Robert B. Bonner" <rbonner at qro.com>
> Subject: Re: [Amps] 3-500z - intermittent filament
> To: "'k7rdx'" <k7rdx at charter.net>, <n4zr at comcast.net>,
> <amps at contesting.com>
> Message-ID: <004c01c74c56$a1905e40$07cf6f18 at cd0209633033>
> Content-Type: text/plain; charset="us-ascii"
>
> Guys,
>
> I have done this countless times for people without wrecking the tube.
>
> Heat the pins with a big soldering iron and gently remove from the tube,
> clean bare pin and tin.  Heat again and clean the inside out thoroughly.
> Mount the pins in a fixture that can handle torch heat and center it. I 
> used
> an old tube socket clamped in a vise.  I already mentioned a fixture could
> be machined that you would heat evenly.  I Used a regular BUNZ-O-MAtic
> Torch.
>
> Utilize either regular solder or Silver solder, if you use silver use STAY
> BRITE, pure silver solder has a HIGHER MELTING POINT THAN TIN / LEAD. 
> PLUS
> you will need to add paste rosin flux instead of the usual plumbing acid
> core the goof at the plumbing shop would try and sell you.
>
> Heat the two pins simultaneously with the torch, fill the pins about 5/8th
> the way full with molten solder and add rosin flux...  Toast the pins up
> good.
>
> Then carefully and without dawdling while still applying heat to the pins
> (You really want that socket clamped safely) push the tube down into the
> pins, using the other pins in the socket as a locator.
>
> I used a hair drier INSTANTLY to start cooling the pins...
>
> Remove tube, polish the pins on the outside, take cold shower...  Not a
> problem, you are now a REAL STUD, a Man's Man, Radio GOD, really cool guy.
>
> However if you drop the tube, blow a seal, burn your hand, start the 
> garage
> on fire...  (or try and do this with the old socket bolted into your 
> SB-220
> my favorite) You'd be three feet below Whale POOP.
>
> BOB DD
>
> -----Original Message-----
> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
> Behalf Of k7rdx
> Sent: Friday, February 09, 2007 7:44 AM
> To: n4zr at comcast.net; amps at contesting.com
> Subject: Re: [Amps] 3-500z - intermittent filament
>
> There is a heat transfer/absorbant compound used in the auto collision
> industry that may work very well for re-soldering filament pins.We used a
> mud like substance to absorb heat when welding in sensitive areas and it
> should be obtainable from most auto body suppliers. When work has been
> completed you can remove with water rinse...Jim
> ----- Original Message ----- 
> From: <n4zr at comcast.net>
> To: <amps at contesting.com>
> Sent: Thursday, February 08, 2007 8:05 AM
> Subject: Re: [Amps] 3-500z - intermittent filament
>
>
>> I'm sure John is correct about both the risks of resoldering and the 
>> ideal
> solution, but what to do if you have tubes that have already failed from
> this cause?
>>
>> Using some of Rich Measures' silver solder and packing the area around 
>> the
> glass seal with wet paper towels, I have successfully repaired several
> tubes.  Last time around, operating on the theory that the spring clips on
> the filament pins might have lost their temper, I swapped them for those 
> on
> grid pins from the same socket.  I also made a point to polish the inside 
> of
> the socket contacts and the filament pins in the hope of reducing the
> resistive heating at that point.  These fixes have so far been effective 
> in
> intense CW and SSB contest use for several years.
>>
>> 73, Pete N4ZR
>>
>> -------------- Original message -------------- 
>> From: "John E. Cleeve" <g3jvc at jcleeve.idps.co.uk>
>>
>> > I would advise caution in resoldering the sleeved pins of the 3-500 et
> al
>> > tubes, for the Eimac spec. and the late Bill Orr, warned that the
> melting
>> > point of the solder used, could be very close to the temperature which
>> > would destroy the glass to metal seal of the filament 
>> > pins..........more
>> > effective electrical contact, between the tube filament pin sleeves and
>> > sockets, with more effective directed forced air cooling of the tube
> base
>> > sockets are the routes to follow.....but this has all be said
>> > before.....regards, John G3JVC.
>> >
>> >
>> > ----- Original Message ----- 
>> > From: "Steve Thompson"
>> > To:
>> > Sent: Thursday, February 08, 2007 12:15 PM
>> > Subject: Re: [Amps] 3-500z - intermittent filament
>> >
>> >
>> > >
>> > >
>> > > terry at g4amt.com wrote:
>> > >
>> > >> The pins are riveted over on the tube side of the `former` so they
> cannot
>> > >> (?) be removed; they are of `split` construction. The only way I
> could
>> > >> re-solder them was to use a solder sucker to extract the old 
>> > >> solder -
> put
>> > >> a
>> > >> couple of drips of flux in the hole and re-solder with silver 
>> > >> solder;
>> > >> heating the pin with a mini-blowlamp ...
>> > >
>> > > A question as to what should be used here? There's 'silver solder' as
>> > > used with a torch for brazing. There's also standard pcb solders with
>> > > added silver content to give them a lower melting point than straight
>> > > tin/lead.
>> > >
>> > > Steve
>> > > _______________________________________________
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>
> ------------------------------
>
> Message: 2
> Date: Fri, 09 Feb 2007 09:30:46 -0500
> From: "Mike McCarthy, W1NR" <lists at w1nr.net>
> Subject: Re: [Amps] 3-500z - intermittent filament
> To: g3rzp at g3rzp.wanadoo.co.uk
> Cc: amps at contesting.com
> Message-ID: <45CC8596.3070102 at w1nr.net>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> Peter Chadwick wrote:
>> There are some higher temperature 'soft solders' around, which don't 
>> require the red heat of hard solder. From memory, something called 
>> 'comsomal' or similar is about a 300 degree C or so solder. Personally, I 
>> much prefer to add cooling air, and use ordinary solder with a heat sink 
>> to keep the seals cool.
>> 73
>> Peter G3RZP
>> _______________________________________________
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>>
>>
> Pb90 (90% lead) solder is about 300 C.  I have had good luck with "Sb5"
> alloy which is 95% tin and 5% antimony.  It is not the highest of
> melting points at about 240 C but much higher than 60/40 at 185 C .
>
> Mike, W1NR
>
>
>
> ------------------------------
>
> Message: 3
> Date: Fri, 09 Feb 2007 07:25:13 -0800
> From: Larry <larry at w7iuv.com>
> Subject: [Amps] test - sorry
> To: AMPS <amps at contesting.com>
> Message-ID: <45CC9259.80809 at w7iuv.com>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> My post keep getting bounced by the list robot. The list administrator
> has declined to answer my requests for assistance and so I'm forced to
> annoy everyone while I try to figure out what's wrong. My apologies.
> -- 
> Larry - W7IUV
> DN07dg
> http://w7iuv.com
>
>
> ------------------------------
>
> Message: 4
> Date: Fri, 09 Feb 2007 07:59:47 -0800
> From: Larry <larry at w7iuv.com>
> Subject: Re: [Amps] General question on filament life
> Cc: Amps <amps at contesting.com>
> Message-ID: <45CC9A73.6000503 at w7iuv.com>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> Maybe I've got my list "bounce" problem fixed.....
>
>
> Around 1970 I put together an amp with a pair of Penta Labs used
> 4-400A's. Around 1988 or so one of the tubes failed due to a filament to
> cathode short. Both tubes were replaced with used Eimac tubes. Still
> using those two tubes. Around 1988 I built up a pair of used Eimac
> 4-400A's in a 40 meter monobander. Around 1999 one of those tubes failed
> due to filament to cathode short. It was replaced with another used
> Eimac tube. Those tubes were in use until a few months ago when that amp
> deck was removed from service.
>
> Both these amps are/were turned on to make and QSO and turned off when
> finished. Some days they may never get turned on, but some days they
> each may see 10 to 12 power cycles. After two failures in 58 tube/years
> I decided to do something about that high failure rate and installed
> step start circuit for the filaments. No failures since then and I still
> turn the things on and off all the time. I have had similar results with
> the 813 amps I use. Always cycle the power, never have had an 813 fail.
>
> Seems to me there are tubes that can handle this sort of treatment IN
> AMATEUR SERVICE and tubes that have a problem. Maybe it's a better idea
> to use a tube that matches your lifestyle rather than alter your
> lifestyle to fit a tube that is to delicate to survive without "special
> care".
>
> For an extreme case take a look at the RCA 6949. The MAXIMUM ALLOWABLE
> inrush surge current is spec'ed at only 165% of the nominal operating
> current!
>
> You guys that like big jugs (toobes, not boobs) and water cooling might
> like this 6949. It requires a minimum of 80 GALLONS PER MINUTE of
> DISTILLED water through the anode cooler, 7 GPM  through the beam
> forming cylinder, and 1 GPM through the socket grid connection!
>
> Back to filament life, when I was still working there was a RF heating
> unit buried deep in a classified area. I only knew about it because a
> pair of 3CX1000's would show up on my buddies desk about once a year. He
> said they would go bad because the filaments were left running all the
> time and anode power was only applied when it was needed. I got a pair
> and checked them and sure enough, NO EMISSION! Seems I've seen this
> written up by Eimac or some other manufacturer. Running thoriated
> tungsten filaments without anode current shortens the life time faster
> than on-off cycling. Any comments on this failure mode?
>
> 73,
>
> Larry - W7IUV
> DN07dg
> http://w7iuv.com
>
>
> ------------------------------
>
> Message: 5
> Date: Fri, 9 Feb 2007 11:03:46 -0500
> From: "Administrator" <amps at myrealbox.com>
> Subject: Re: [Amps] test - sorry
> To: "'Larry'" <larry at w7iuv.com>, "'AMPS'" <amps at contesting.com>
> Message-ID: <001c01c74c63$e3eb2420$0b80a8c0 at laptop>
> Content-Type: text/plain; charset="us-ascii"
>
>
> Larry,
>
> Your posts are apparently falling into one of three categories:
>
> 1) coming from an address that is not subscribed to the list
> 2) have excessive addressees (to many CC:)
> 3) are over 20K in size (excessive quoting or HTML).
>
> A notice was posted here just last week due to the number of
> posts that were falling into those categories.  See message:
> http://lists.contesting.com/pipermail/amps/2007-February/056571.html
>
> You have not sent any request for information or help to
> amps-at-myrealbox.com which is my direct e-mail as posted
> on the list information page.  "amps-owner-at-contesting.com" is
> spam filtered (and not checked on a regular basis) because the
> spambots hit it as hard as the main list address.
>
> Administrator
> amps at contesting.com
>
>
>
>
>> -----Original Message-----
>> From: amps-bounces at contesting.com
>> [mailto:amps-bounces at contesting.com] On Behalf Of Larry
>> Sent: Friday, February 09, 2007 10:25 AM
>> To: AMPS
>> Subject: [Amps] test - sorry
>>
>>
>> My post keep getting bounced by the list robot. The list
>> administrator
>> has declined to answer my requests for assistance and so I'm
>> forced to
>> annoy everyone while I try to figure out what's wrong. My apologies.
>> -- 
>> Larry - W7IUV
>> DN07dg
>> http://w7iuv.com
>> _______________________________________________
>> Amps mailing list
>> Amps at contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
>>
>
>
>
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> End of Amps Digest, Vol 50, Issue 25
> ************************************
> 