[Amps] filament instant heating query
Carl
km1h at jeremy.mv.com
Fri Jun 15 09:34:15 PDT 2012
It is the Impedance that controls things Jim.
A properly designed transformer will supply its rated voltage AND rated
current when its connected to a "matched load" Its no different than a
transmitter in that area.
So your Clipperton has a load requiring 6.3V@ 16A and that happens only when
the filaments are up to temperature. Before that when the filament
resistance is much lower and the transformer can not meet the current
requirements so the voltage sags. What you have is a built in variable step
start.
Now you take a poorly designed/marketed amp such as the AL-80A/80B which
runs the filament voltage high to start with so it can meet its inflated
1000W PEP rating. The end result is that it forced a step start to be
included in late AL-80A production and all 80B's. The filament is still over
spec in standby using the factory set transformer taps and using a bucking
winding will bring it down to 5.0 no load at the socket and 4.8V at full
power out.The end result is a bit less RF but hopefully much longer tube
life.
Dentron ran high with the DTR-2000L and several other amps that were built
when the AC line was 115-117Vand 230-234V are now a bit over spec.
When you get into the big instant on tungsten filament tubes such as the
3CX3000A7 and up is when a step start is really required.OTOH a cathode tube
such as the popular YC-156 takes 6-8 minutes to slowly warm up so no step
start is needed except maybe for the plate supply.
Anybody that tells you a SB-220 can bend the 3-500 filament helix at turn on
has definitely been dropped on his head way too many times. That transformer
was particularly designed to provide a soft ramp up. I dont know about Dahl
replacements.
Your 572B filament will fail when it becomes too thin to support itself or
you drop it. It will more likely loose emission long before that resulting
in gradual loss of output.
Carl
KM1H
----- Original Message -----
From: "Jim Hargrave" <w5ifp at gvtc.com>
To: <amps at contesting.com>
Sent: Friday, June 15, 2012 10:27 AM
Subject: Re: [Amps] filament instant heating query
> Well,
>
> I'll chime in on this one with personal experience.
> Regardless of whether you believe in the "Myths" or not.
> Most are not supported with facts.
>
> I have a Clipperton-L purchased new in 1980. It is in daily
> use and still has the four original 572B tubes. It is
> original and does not have any form of slow start. Also
> the four tubes are even mounted in a horizontal position.
>
> I assume the inductance of the transformer has some control
> of the in-rush current. I do know these tubes do not exhibit
> any visible form of high light intensity when first turned on.
>
> Based on the "Myths" perhaps someone could compute and tell me
> when one of them might have a filament failure?
>
>
>
> 73s de Jim
> W5IFP
>
>
>
> > -----Original Message-----
> > From: amps-bounces at contesting.com
> [mailto:amps-bounces at contesting.com]On
> > Behalf Of Carl
> > Sent: Friday, June 15, 2012 8:11 AM
> > To: amps at contesting.com; Bill Fuqua
> > Subject: Re: [Amps] filament instant heating query
> >
> >
> > Amen to that.
> >
> > There seems to be more belief of myths recently in the ham
> > field than before
> > and I suspect a good part is from AG6K's absolute pathetic
> > nomsense that is
> > read by the totally uninformed and it becomes doctrine.
> >
> > Carl
> > KM1H
> >
> >
> > ----- Original Message -----
> > From: "Bill Fuqua" <wlfuqu00 at uky.edu>
> > To: "Charles Harpole" <k4vud at hotmail.com>;
> > <amps at contesting.com>; "David
> > Springer" <dspringer at cfl.rr.com>
> > Sent: Friday, June 15, 2012 12:49 AM
> > Subject: Re: [Amps] filament instant heating query
> >
> >
> > > Myth Busters did an experiment with light bulbs to see how they were
> > > affected by switching some on and off and others left on.
> > > Practically no difference.
> > > I believe this mostly started with light bulbs because when once
> the
> > > filament gets so thin at some point due to the evaporation of the
> > > tungsten the next time you turn it on and you have a surge of
> > current in
> > > the lamp it burns into. This thin area has a higher resistance
> > > than the rest of the filament and gets hotter.
> > > I don' think there is any real rocket science, molecular physics or
> > > quantum mechanics to it.
> > > 73
> > > Bill wa4lav
> > >
> > >
> > > At 03:59 AM 6/15/2012 +0000, Charles Harpole wrote:
> > >
> > >>to check on a supposition............
> > >>
> > >>
> > >>
> > >>It appears possible that the sudden application of voltage to a tube
> > >>filament causes degradation of the filament.
> > >>
> > >>
> > >>
> > >>What seems to happen? Is it possible that the very rapid heating of
> a
> > >>filament could cause so much quick molecular action (rapid increased
> > >>bouncing around of the molecules) that the shape of the
> > filament could be
> > >>changed? A deformed filament could then be too close to
> > other components
> > >>to cause an arc, perhaps?
> > >>
> > >>
> > >>
> > >>Or is the action on the atomic level...i.e., does heat change
> > the actions
> > >>of electrons in an atom?
> > >>
> > >>
> > >>
> > >>But, maybe the filament rapid heating works just fine, and all of the
> > >>"slow start" "inrush protection" circuits are a waste?
> > >>
> > >>
> > >>
> > >>Another inquiring mind wants to know.
> > >>
> > >>73,
> > >>
> > >>Charles Harpole
> > >>k4vud at hotmail.com
> > >>_______________________________________________
> > >>Amps mailing list
> > >>Amps at contesting.com
> > >>http://lists.contesting.com/mailman/listinfo/amps
> > >
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> > >
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