[TMC] Lamps

[Richard Knoppow]

----- Original Message ----- 
From: "Roy Morgan" <k1lky68 at gmail.com>
To: "Larry" <Telegrapher at Q.com>
Cc: <TMC at mailman.qth.net>
Sent: Monday, July 14, 2014 8:47 AM
Subject: Re: [TMC] Lamps



On Jul 12, 2014, at 4:32 PM, Larry <Telegrapher at Q.com> 
wrote:

> Anyone know of a source for the 3S6 3W 120V lamps that go 
> in the power supply of the PAL-500/350? ... They lamps 
> have the double button on the bottom and are the B15 base 
> bayonet style.


Larry,

My Google search turns up many hits for the screw in similar 
lamp.

But these guys seem to the double contact bayonet lamp for 
53 cents each:
<https://www.1000bulbs.com/product/1090/IN-0003S65DC120.html?utm_source=SmartFeedGoogleBase&utm_medium=Shopping&utm_term=IN-0003S65DC120&utm_content=DC+Bayonet+Base+S6+and+S11+Indicator+Lamps&utm_campaign=SmartFeedGoogleBaseShopping&gclid=COPyyN6Qxb8CFUYA7AodSmEAmA>

(Shipping charges not checked.)

May I offer my Morgan’s Law of Inverse Perversity about 
spares for your consideration:

Morgan's Law of Inverse Perversity:

If you have no spare for a critical part or tube, that part 
will fail at the most inopportune time.
If you do have a spare, or spares, the original one will 
never fail and you'll never use the spare.

Further comments:

1) Just the right 2 watt resistor in series with the lamp 
will make it last essentially forever.
2)  Order a dozen or so.  If you store them close to or in 
the power supply, their presence will influence the running 
lamp to  run forever.  (Yes, it is a kind of magic.)
3)  If you find a spare power supply for the PAL-350, I will 
be very tempted to pay shipping.
4)  Grainger would charge you $6 for the screw in similar 
lamp
5)  Is it Mouser who has no shipping charges?

Roy
Whose supply-less PAL-350 may remain forever cold.


Roy Morgan
RoyMorgan at alum.mit.edu
K1LKY Since 1958

    I also did a Google search but didn't find anything.
    I don't have the schematic for this power supply among 
my collection. What is the purpose of the lamps?  Sometimes 
tungsten filament lamps are used as current regulators in 
which case a resistor in series is not possible. When used 
for illumination the life of a pure tungsten filament in a 
lamp or tube will be doubled for a 5% reduction in voltage 
and extended more than ten times for a 15% reduction.  5% 
makes no perceptable difference in brightness. 15% does but 
its usually acceptable.  In tubes the reduction can be used 
only with bright tungsten filaments. The amount that can be 
used depends on the emission of the tube.  Around WW-2 RCA 
used to publish charts in their advertising and elsewhere 
showing the life vs: filament voltage. Note that small 
_increases_ in voltage shorten life very considerably.
    Another thought:  Hewlett-Packard used similar lamps as 
the regulators in the famous -hp- RC oscillator circuit 
invented by Bill Hewlett. I am not sure about the wattage 
and more than one kind of lamp was used in various 
instruments.  If you need to replace a lamp in one of these 
oscillators the -hp- aging procedure was to run the lamp 
from a variable low voltage transformer and run it up to 
just visiable red heat. Hold it at that temperature for 
several seconds and then back the voltage down slowly. This 
takes the strains out of the filament.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com