[Amps] General question on filament life

Mon Feb 12 13:44:38 EST 2007

Hi,
I hope this does not go too far off subject, many years ago I worked in the 
labs for a large lamp manufacturer and observed in that time some fairly 
wierd failure mechanisms. One of them that I remember solving was an 
incandescant strip light that seemed to have a problem on 60Hz supply but 
was ok on UK mains (50Hz).
Incidentally at the time lamps were life-tested on AC but light output was 
measured on a photometer with the lamp under test operating from DC.
The problem with this particular lamp proved to be a mechanical resonance in 
the filament, when hot it had a resonance at about 60Hz which meant that it 
shook like hell when in a typical ferrous diffuser assembly with any 
significant magnetic field in it. I wonder if these cases observed with 
dimmers are affected by the relatively high peak currents seen in the 
filaments despite the low operating temperature of the lamps. Perhaps these 
current spikes mechanically kick the filament?

Due to the temperature / resistance characteristics of tungsten it is 
feasible that some of the filament momentarily reaches an above normal 
temperature on switch on, certainly in lamps the parts of the filament away 
from the supports run hotter than those in contact with them, this causes 
these parts of the filament to evaporate at an increased rate which in turn 
causes the hotspots to get even hotter. I would surmise (though I may be 
wrong) that on switch on some valves briefly overheat parts of the 
filament/heater. This would suggest that a very slow ramping up of heater 
voltage may be beneficial by either the use of a timer circuit of sorts or a 
current limited supply. I guess it is also feasible that the inrush currents 
give the contacts in the bases a hard time too.

FWIW many years ago a customer wanted to know the relationship between 
applied voltage and power consumption of a tungsten filament lamp. I 
produced a plot from measurement and it was surprising to say the least, I 
am sure someone on this reflector with an hour to spend could do a plot to 
confirm this.

Sorry once again to perhaps deviate from the initial subject, however I 
suspect that the effects of inrush current may be a big influencing factor 
when deciding whether an amplifier should be left on standby or cycled on 
and off when needed. A valve with a small heater requirement like a 4CX250 I 
am sure could be supplied from a small 3 legged regulator with the current 
limit offering adequate protection. However some of the bigger valves that 
are often mentioned on here would be difficult to cater for in the same way.

Regards David G0FVT

----- Original Message ----- 
From: <amps-request at contesting.com>
To: <amps at contesting.com>
Sent: Monday, February 12, 2007 5:00 PM
Subject: Amps Digest, Vol 50, Issue 33

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> Today's Topics:
>
>   1. Through the p?st darkly ( Robert B. Bonner )
>   2. Re: 87A for sale/sold (bob finger)
>   3. 3-400Z snapped off grid pin!! (Van K7VS)
>   4. Alpha 87A - fault 9 (Carsten Esch)
>   5. seeking transistors (StephenTetorka at cs.com)
>   6. Re: 1 tube or two ?? (EP Swynar)
>   7. Re: General question on filament life: comments (Harold  Mandel)
>   8. Re: Lamps and surge protection (Harold  Mandel)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Mon, 12 Feb 2007 14:58:41 +0000
> From: " Robert B. Bonner " <rbonner at qro.com>
> Subject: [Amps] Through the p?st darkly
> To: Amps at contesting.com
> Message-ID:
> <787266975-1171292300-cardhu_blackberry.rim.net-220268424- at bwe005-cell00.bisx.prod.on.blackberry>
>
> Content-Type: text/plain
>
> 807 amp then a pair of 813's follows by four. A couple 4-400's then 
> converted to 3-500's a 3-1000 then a pair. A pair of 8877's then 
> 3CX1200's. 3X3. 3X10. Then YC-156 back to 8877's. Never did 4X1's myself. 
> I might have missed something. All the other tubes were reworks or 
> something like that. BOB DD
> Sent From Mobile Device
>
>
>
> ------------------------------
>
> Message: 2
> Date: Mon, 12 Feb 2007 10:09:27 -0500
> From: bob finger <finger at goeaston.net>
> Subject: Re: [Amps] 87A for sale/sold
> To: Amps <Amps at contesting.com>
> Message-ID: <45D08327.4070502 at goeaston.net>
> Content-Type: text/plain; charset=ISO-8859-15; format=flowed
>
> Amp is sold.  Thanks.  73 bob de w9ge
>
>> I am putting my Alpha 87A on the block.
>
>
>
> ------------------------------
>
> Message: 3
> Date: Mon, 12 Feb 2007 07:17:25 -0800
> From: "Van K7VS" <wa7fab at cdsnet.net>
> Subject: [Amps] 3-400Z snapped off grid pin!!
> To: <amps at contesting.com>
> Message-ID: <000a01c74eb8$e7c84800$6500a8c0 at FAMILY2>
> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> reply-type=original
>
> I have a perfectly good 3-400Z that is missing one of the three grid pins
> (snapped off close to tube base ((about 3/8" still protruding)) that I was
> wondering if I can still use in my old Loudenboomer single ended grounded
> grid amplifier.  Any reason why it can't be used since all three grids are
> tied together internally in tube and all three grid pins go directly to
> ground on socket.
>
> Van
>
>
>
> ------------------------------
>
> Message: 4
> Date: Mon, 12 Feb 2007 16:22:32 +0100
> From: "Carsten Esch" <carsten.esch at appello.de>
> Subject: [Amps] Alpha 87A - fault 9
> To: <amps at contesting.com>
> Message-ID: <007401c74eb9$a0aff1b0$14b2a8c0 at carsten>
> Content-Type: text/plain; charset="us-ascii"
>
> Hi,
>
> a friend of mine has a problem with his 87A. He gets a fault 9. Manual 
> says
> "transmit PIN diode forward current below minimum".
>
> Does anyone knows how to fix the problem?
>
> Thanks!
>
> Carsten, DL6LAU
>
>
>
> ------------------------------
>
> Message: 5
> Date: Mon, 12 Feb 2007 11:13:55 EST
> From: StephenTetorka at cs.com
> Subject: [Amps] seeking transistors
> To: amps at contesting.com
> Message-ID: <cb3.af81364.3301ec43 at cs.com>
> Content-Type: text/plain; charset="US-ASCII"
>
> Need 2 each SRFJ7004 for my 706...anybody have'em
>
> Tnx.
> Steve
> WA2TAK
>
>
> ------------------------------
>
> Message: 6
> Date: Mon, 12 Feb 2007 11:15:31 -0500
> From: "EP Swynar" <gswynar at durham.net>
> Subject: Re: [Amps] 1 tube or two ??
> To: <amps at contesting.com>
> Message-ID: <003c01c74ec2$c5104bf0$70305a45 at SwynarComputer>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Hi All,
>
> I have nothing at all against the use of newer tubes whatsoever...however,
> there IS a point that nobody has touched upon that merits consideration, 
> and
> that is the PRICE of the active device(s) we might wish to build an
> amplifier around...
>
> Sure, a 4-1000A, 813, 4-400, etc. may be "...old-fashioned" compared to
> to-day's tubes, but I'm retired, I'm frugal, and I'm especially nostalgic
> about the "old fashioned" prices these jugs can still be had for to-day
> (assuming, of course, you're a wisened shopper).
>
> Sure, we'd all dearly love to drive the big Benz's / Beemers / Ferraris / 
> et
> al in our dreams, but let's face it, most of us only have lowly Chevy's,
> Toyotas, & pick-ups parked in our driveways...yet these vanilla vehicles
> will transport us from point "A" to "B", just as readily as a kilowatt 
> will
> send our signals from point "A" to point "B", be that signal from a 
> 4-1000A,
> or an 8877...
>
> Meanwhile, I continue to buy the odd lottery ticket here & there, with my
> fingers crossed!
>
> ~73~ Eddy VE3CUI - VE3XZ
>
>
>
> ------------------------------
>
> Message: 7
> Date: Mon, 12 Feb 2007 11:28:51 -0500
> From: "Harold  Mandel" <ka1xo at juno.com>
> Subject: Re: [Amps] General question on filament life: comments
> To: "'Steve Thompson'" <g8gsq at eltac.co.uk>, <amps at contesting.com>
> Message-ID: <002d01c74ec2$e43c2f80$750ca8c0 at laptopHM>
> Content-Type: text/plain; charset="us-ascii"
>
> Steve,
>
> The modified sawtooth waveform from a dimmer
> would seem to stress the metallic filament of a tungsten
> bulb more.
>
> Let's compare the waveform of pure D.C.,  versus a sine wave,
> versus a sawtooth wave, each being loaded by a tungsten
> wire that provides resistance.
>
> I don't know this, so it's why I'm posting.
>
> Would not the quanta of change, (highest being the sawtooth,
> lowest, D.C. ), affect the molecular viability of the filament
> in a bulb?
>
> Discounting the inrush parameters, entirely, and applying the
> best means of ramping up the filament to operating voltage,
> the question focuses on the stress caused a filament by
> either a non-oscillating waveform, a smooth waveform or a
> waveform with spikes.
>
> Please advise.
>
> Thanks,
>
> Hal
>
> [snip]
> What might be the burn out mechanism? The thermal time constant of the
> bulb filament is much longer than the 50/60 cycle applied voltage, so I
> can't see that it's thermal. Steve
> [snip]
>
>
>
>
> ------------------------------
>
> Message: 8
> Date: Mon, 12 Feb 2007 11:32:36 -0500
> From: "Harold  Mandel" <ka1xo at juno.com>
> Subject: Re: [Amps] Lamps and surge protection
> To: "'John Nelson'" <john at crew-green.com>, <amps at contesting.com>
> Message-ID: <002e01c74ec3$68d88cc0$750ca8c0 at laptopHM>
> Content-Type: text/plain; charset="us-ascii"
>
> John,
>
> When  testing transformers in my younger days I remember
> learning to not touch the winding conductors even though it
> was just a multimeter's test voltage being applied.
>
> Perhaps the connection from an inductive device is
> providing some sort of energy spike in the 6.3 v.a.c.
> transformer supply that isn't there in the other supply?
>
> Hal
>
> [snip]
> One of my amplifier PSCUs has six meters on the front panel, each backlit
> via two small 6V wire-ended bulbs. These are fed from an internal rail 
> which
> ramps up to +5V in about ten seconds or so. This PSCU has been in regular
> service since 1980 and none of its meters have yet needed a bulb change. A
> low-voltage PSU has two similarly backlit meters with 12V bulbs fed 
> directly
> from a 6.3VAC winding. One or other seems to fail every few months. John.
> [snip]
>
>
>
>
>
> ------------------------------
>
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