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@contesting.com>
To: <amps@contesting.com>
Sent: Monday, February 12, 2007 5:00 PM
Subject: Amps Digest, Vol 50, Issue 33
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> When replying, please edit your Subject line so it is more specific
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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@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@qro.com>
> Subject: [Amps] Through the p?st darkly
> To: Amps@contesting.com
> Message-ID:
> <787266975-1171292300-cardhu_blackberry.rim.net-220268424-@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@goeaston.net>
> Subject: Re: [Amps] 87A for sale/sold
> To: Amps <Amps@contesting.com>
> Message-ID: <45D08327.4070502@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@cdsnet.net>
> Subject: [Amps] 3-400Z snapped off grid pin!!
> To: <amps@contesting.com>
> Message-ID: <000a01c74eb8$e7c84800$6500a8c0@FAMILY2>
> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> reply-type=original
>
> I have a perfectly good 3-400Z that is missing one of the three grid pins
> (snapped off close to tube base ((about 3/8" still protruding)) that I was
> wondering if I can still use in my old Loudenboomer single ended grounded
> grid amplifier. Any reason why it can't be used since all three grids are
> tied together internally in tube and all three grid pins go directly to
> ground on socket.
>
> Van
>
>
>
> ------------------------------
>
> Message: 4
> Date: Mon, 12 Feb 2007 16:22:32 +0100
> From: "Carsten Esch" <carsten.esch@appello.de>
> Subject: [Amps] Alpha 87A - fault 9
> To: <amps@contesting.com>
> Message-ID: <007401c74eb9$a0aff1b0$14b2a8c0@carsten>
> Content-Type: text/plain; charset="us-ascii"
>
> Hi,
>
> a friend of mine has a problem with his 87A. He gets a fault 9. Manual
> says
> "transmit PIN diode forward current below minimum".
>
> Does anyone knows how to fix the problem?
>
> Thanks!
>
> Carsten, DL6LAU
>
>
>
> ------------------------------
>
> Message: 5
> Date: Mon, 12 Feb 2007 11:13:55 EST
> From: StephenTetorka@cs.com
> Subject: [Amps] seeking transistors
> To: amps@contesting.com
> Message-ID: <cb3.af81364.3301ec43@cs.com>
> Content-Type: text/plain; charset="US-ASCII"
>
> Need 2 each SRFJ7004 for my 706...anybody have'em
>
> Tnx.
> Steve
> WA2TAK
>
>
> ------------------------------
>
> Message: 6
> Date: Mon, 12 Feb 2007 11:15:31 -0500
> From: "EP Swynar" <gswynar@durham.net>
> Subject: Re: [Amps] 1 tube or two ??
> To: <amps@contesting.com>
> Message-ID: <003c01c74ec2$c5104bf0$70305a45@SwynarComputer>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Hi All,
>
> I have nothing at all against the use of newer tubes whatsoever...however,
> there IS a point that nobody has touched upon that merits consideration,
> and
> that is the PRICE of the active device(s) we might wish to build an
> amplifier around...
>
> Sure, a 4-1000A, 813, 4-400, etc. may be "...old-fashioned" compared to
> to-day's tubes, but I'm retired, I'm frugal, and I'm especially nostalgic
> about the "old fashioned" prices these jugs can still be had for to-day
> (assuming, of course, you're a wisened shopper).
>
> Sure, we'd all dearly love to drive the big Benz's / Beemers / Ferraris /
> et
> al in our dreams, but let's face it, most of us only have lowly Chevy's,
> Toyotas, & pick-ups parked in our driveways...yet these vanilla vehicles
> will transport us from point "A" to "B", just as readily as a kilowatt
> will
> send our signals from point "A" to point "B", be that signal from a
> 4-1000A,
> or an 8877...
>
> Meanwhile, I continue to buy the odd lottery ticket here & there, with my
> fingers crossed!
>
> ~73~ Eddy VE3CUI - VE3XZ
>
>
>
> ------------------------------
>
> Message: 7
> Date: Mon, 12 Feb 2007 11:28:51 -0500
> From: "Harold Mandel" <ka1xo@juno.com>
> Subject: Re: [Amps] General question on filament life: comments
> To: "'Steve Thompson'" <g8gsq@eltac.co.uk>, <amps@contesting.com>
> Message-ID: <002d01c74ec2$e43c2f80$750ca8c0@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@juno.com>
> Subject: Re: [Amps] Lamps and surge protection
> To: "'John Nelson'" <john@crew-green.com>, <amps@contesting.com>
> Message-ID: <002e01c74ec3$68d88cc0$750ca8c0@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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> End of Amps Digest, Vol 50, Issue 33
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