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Re: [TenTec] solid-state lamps for TT

To: <tentec@contesting.com>
Subject: Re: [TenTec] solid-state lamps for TT
From: w8au@sssnet.com
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Wed, 08 Feb 2006 23:30:21 -0500
List-post: <mailto:tentec@contesting.com>
At 07:39 PM 2/8/06, Rick Williams wrote:
>I'd be curious to see how these lamps perform.  I looked at similar
>drop in replacements but I was concerned that the beam width would be too 
>narrow to illuminate the Ten-Tec meters.  Most of the light would go
>straight up rather than at 90 degrees towards the meter back.

You could be right. (I haven't used the drop-ins)

When one of my TT rig meter lamps go out, (or any other gear) I replace 
them by hardwiring at least two white LEDs in parallel with enough dropping 
resistance to get 15ma or so, depending on the diode peak current 
rating.  I don't use the socket, but solder the 1/2W resistor in series 
with the diodes from the 12V connection to ground (or bulb socket 
housing).  I position the diodes horizontally about an inch and a half 
behind the meter, pointing them toward the meter back.  (The stiffness of 
the diode and resistor leads holds them in place)  Then comes the physical 
positioning to get the 30 degree light pattern from each to flood as much 
of the meter face as possible.  Works well.  Three diodes would be even better.

Stringing the LEDS in series would be even more efficient if the voltage 
drop across each LED was equal or close to it.  This would keep the light 
emissions equal.

For edgewise meters as used on the TT SP-325, ONE LED stuffed into the 
meter back in place of the old grain-o-wheat lamp illumines everything.
But these particular edgewise meters are not tinted a darker color so the 
resulting "blue" white light can be irritating as 15ma generates excessive 
brilliance.  Reducing current is the answer here.

I find huge assortments of LEDs at Hosfelt electronics, Steubenville, OH, 
and pricing isn't bad.  www.hosfelt.com

Hope these notes help those that haven't tried it yet.

Perry  w8au 

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