Jerry...they are hard-wired, but inside of the meter case itself. TT will
sell you a LED package for 10 bucks that is a direct wiring replacement for
the original incandescent lamp. But....you still need to do a PITB tear
down to get to the meters. (Titan III)
73 John W4II
----- Original Message -----
From: "Dr. Gerald N. Johnson" <geraldj@weather.net>
To: <tentec@contesting.com>
Sent: Thursday, March 11, 2010 8:39 PM
Subject: Re: [TenTec] Titan III screen current question.....
> The TT manual that I downloaded only identifies the lamps on the
> schematic and shows them separate from the meter and the meter wiring.
> The lamps are hard wired to the 12 volt supply but the meters plug into
> the meter switch board A12.
>
> Tiny 12 volt lamps can be had in hobby shops for train lighting or for
> scale doll house lighting as well as sometimes at Radio Shack. Many
> different 12 volt lamps in tiny packages can be bought from Mouser and
> Digi-Key.
>
> Its worth selecting a lamp with a long rated lifetime, though that will
> reduce its illumination efficiency.
>
> It can also be worth dropping the supply voltage about 10% with a series
> resistor which will also lengthen the life by lowering the operating
> temperature and limiting the lamp surge current. A typical incandescent
> lamp's cold resistance is in the range of 15 to 16 times lower than its
> operating resistance. So a lamp rated to draw 100 milliamps will draw at
> least 1.5 amps the instant its connected, unless the external circuit
> limits that current, and nearly all incandescent lamp failures seem to
> be at power on.
>
> So if that 100 mil rated lamp at 12 volts had a 12 ohm series resistor
> the peak surge current would be limited to about 0.6 amp. And the 10%
> drop in operating voltage would quadruple the lamp life. Rule of thumb
> from a GE lamp book years ago is that a 5% change in lamp voltage causes
> a 10% change in light output and if going down in voltage a doubling of
> life or if going up, halfing the life.
>
> 73, Jerry, K0CQ
>
> On 3/11/2010 2:33 PM, Jim Brown K9YC wrote:
>> On Thu, 11 Mar 2010 12:09:08 -0600, John wrote:
>>
>>> TT does not stock the original incandescent meter lamps.
>>
>> What's the mfr/part number of the lamp? Is it a standard industry type?
>> Older Ten Tec gear (Titan 425, Herc I, Herc II, 229 and 238 tuners) all
>> use
>> standard bayonet lamps that are easy to source from industrial vendors. I
>> simply buy boxes (a dozen or so lamps per box) of 14V long life bulbs. I
>> replaced all the bulbs in one 229B with LEDs and series resistors, but am
>> not
>> satisfied with the result, so I've stuck with incandcescents in the other
>> four. YMMV.
>>
>> 73,
>>
>> Jim K9YC
>>
>>
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