[TenTec] Better Bulb Life in TenTec 229, 238 Tuners

[Dr. Gerald N. Johnson]

On Fri, 2008-02-15 at 22:23 -0500, Carter, K8VT wrote:
> Ralph,
> Pardon me if this is a silly question, but you've confused me a bit...
> 
> First, you say:
> 
> Ralph Matheny wrote:
> >  I'd never want a diode of *any* [my emphasis added] flavor inside an 
> antenna tuner if I
> >  could avoid it. Everytime I flow current thru a diode I get NOISE
> >  someplace.
> 
> Then you say:
> 
> >  I've not tried  the new LEDS, they are a bit expensive I
> >  think but should be a good solution.
> 
> Here's my confusion -- You say you wouldn't have -any- diode inside an 
> antenna tuner  but then you say an LED should be a good solution. Aren't 
> LEDs diodes as in (L)ight (E)mitting *(D)IODES*? Won't it also generate 
> noise, along with the light?
> 
> Thanks for any 'light' you may be able to shed on this issue!   :-)
> 
Since that LED is rated to work from 6 to 36 volts, and ac/dc, there's a
good chance it has a rectifier, and a current regulator. Since the
package doesn't have room for a heat sink, its almost sure the current
regulator is a switching regulator probably running at a 1/2 MHz or
faster rate for all those works to fit inside the lamp assembly. It
might be a whole lot noisier than the forward noise of a diode. Diodes
along don't tend to be noisy when forward biased, its when they are
reverse biased and beginning to break down that they get NOISY! And the
last I checked the PIV of a LED (true any way for red LEDs from the
1980s) was not much more than its forward drop, just a few volts.

73, Jerry, K0CQ