[Amps] General question on filament life

[John E. Cleeve]

I base my treatment of valve/tube heaters, on the way the filament life of 
16mm cine projector high wattage bulbs could be considerably extended if 
they were brought up to full brightness slowly......50 years ago, in the 
days before SCR's, and in the particular college situation I was in, we had 
four 16mm projectors in virtually continuous use, I arranged for each 
projector lamp house to have a dedicated switch box which contained nichrome 
wound resistors, which at switch on, were all in series in the filament 
circuit, when the power was applied, and the film leader began to run 
through the projector gate,  the projector bulb filament gradually began to 
glow, and the resistors were then quickly switched out of circuit,  the bulb 
was then at full brightenss by the time "3" had reached the 
gate.....treating the projector bulbs in this way, extended their working 
life until they were beginning to discolour internally, as opposed to the 
normal "failure at switch on" or, the 12 - 25 hour life we had been 
experiencing.......I know that thoriated tungsten filaments, and other 
specialist materials used in the manufacture of transmitting valve filaments 
may be quite different, and cost a lot more than the materials used in 
projector bulbs, however, in my view, this was usefull experience in being 
able to control the current "surge" at switch on, and extend the life of an 
item which was very expensive........regards, John G3JVC.

----- Original Message ----- 
From: <Gudguyham at aol.com>
To: <rbonner at qro.com>; <garymyers at powerc.net>; <amps at contesting.com>
Sent: Thursday, February 08, 2007 11:30 PM
Subject: Re: [Amps] General question on filament life


>
> In a message dated 2/8/2007 3:25:42 P.M. Eastern Standard Time,
> rbonner at qro.com writes:
>
> How many  bulbs have you had fail the first time you turned it ON?  I have
> had a  lot.  When you are cycling, you will have results all over the  map
> whether you step start it or not as each tube is an individual.   Some die 
> at
> birth, and some live to be 114 years  old.
>
>
>
> I have been thinking about this subject a lot myself.  This is what I 
> have
> concluded.  Since ham radio is an occasional thing we do with little 
> transmit
> time compared to off time or listening time.  Seems like it would  be
> senseless to leave your filaments running 24/7.  On the other hand if  you 
> cycled them
> a lot that could be costly too, so for hams as Bob says it  probably makes
> little difference.  But I think the ideal situation would be  to turn off 
> the
> filament when not in use and to bring the filament up slowly  with a 
> variac to
> proper operating voltage every time you use the amp.  It  would be a pain 
> to do
> that every time, but all that hassle aside, it might be  "the best" thing.
> Of course you could argue that one mistake could be  costly, but I am 
> speaking
> only as everything being perfect.  It's just not  practical though.
>
> For what is it worth, here is what I do.  When I go on the air I do  not 
> turn
> on the amplifier unless I need to use it.  If I know I am going to  use 
> it, I
> will then turn it on, it will stay on until I am done hamming for that
> session.  I won't shut it off if I know I might be using it again even an 
> hour
> later like after dinner or something.  I would NOT cycle it on and off  as 
> I
> needed it for a hamming session.  This is why I always put a standby 
> switch on
> all my SB-220 amps.  Many times I did not use the amp and then  suddenly I 
> would
> and then again I would not.  The standby switch came in  handy so I didn't
> have to cycle the filaments.  You all notice that USUALLY  when a light 
> bulb
> burns out it is when you first turn it on.  Only my 2  cents.  Lou
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