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Re: [Amps] More on "baby ur radio"

Subject: Re: [Amps] More on "baby ur radio"
From: "Roger (K8RI)" <>
Date: Wed, 23 Dec 2015 20:05:13 -0500
List-post: <">>
Semiconductor device aging is not a yes or no question. To pick nits, Yes they all do, but at vastly different rate when used within their ratings.

As has been noted, The certainly do last far longer than tubes. Compare the maintenance of tube type radios, TVs, and rigs of the 50s, 60s, and 70s to today's equivalent. Tube replacement in the early top end Collins and Hallicrafters rigs was common. Today, transistor failure is rare. Finals are a special issue.

But to the specifics of semiconductor aging. It would take a long article to address transistor aging properly, but most of today's transistors and devices as discrete transistors are the minority of the semiconductor devices used and age from an entirely different reason than early devices known as the 3 leg fuse.

In the early days the problems were primarily from impurities in the semiconductor material. Purity levels in those "early days" (1950s into the late 1970s) for production materials were on the order of several parts per billion, which improved to around tenths of a part per billion. Today I understand they are into the few parts per Trillion.

I'll try to keep this on the typical ham level of the news groups, which means I'll need to leave out a lot of the details. I'm speaking strictly about bi-polar transistors. A search can give far more detail. Typically semiconductor devices consist of "N" and "P" type materials. An NPN transistor can be thought of as a low voltage triode tube without the vacuum. A material, called a "dopant" ( ) , is added to pure Silicon to make it either N or P type. But all pure silicon is not "pure". Whether N, or P type a tiny amount of the other material exists in there as well. In those early transistors the impurities were considerable compared to today's materials.

NOTE: Tubes are voltage devices and transistors are current devices. Exceptions can be found.

The junction where the N and P type materials meet is tiny. It's on the molecular level. The P type "dopant" will tend to migrate across the junction to the N-type material, contaminating the N-type. This occurs with age and is bi-directional, but is accelerated with increased temperature.

This cross contamination was the primary reason for aging in early semiconductors.

Technically the cross contamination still happens in junction type transistors, but with today's purity levels the rate is so low that it can normally be ignored with transistors lasting far longer than we do.

There are other reasons for aging, but an explanation gets complicated and their contribution is normally miniscule to devices with very long lifetimes.

There is a new type of aging in some devices. With some devices operating well into the GHz range, the device may consist of very small components, measured in the micron range. They are so tiny that electron travel actually causes wear. Computer CPUs are now typically running into the GHz range. That "chip" may contain many millions of transistors so small it would take a microscope to see them.

This certainly must have an effect on ham communications up in the GHz range. Who ever thought we'd see circuits so small that electrons going around a corner could cause a wear problem

For a background, I worked in the semiconductor industry for over 26 years. I have a Bachelors degree in Computer Science with a Math minor. Please excuse my one handed typos and spelling errors. I make my own worst proof reader.


Roger  (K8RI)

On 12/17/2015 Thursday 7:59 PM, Charles H wrote:
On this reflector, I have poo-pooed the idea of baby-ing your radio especially 
by turning it off often, lowering xmit power, etc.
However, I read that with ordinary tubes, the chemistry of the cathodes and filaments are affected 
by life-of-use, so that tubes do "wear out" with use.  Tubes can be rated in terms of 
"hours of use" with the type in a KWM-2 rated at around 2,000 hours of useful function.  
Thorium in the chemical make-up of the metal parts in a tube, maybe a metal or ceramic tube 
(usually added to higher power tubes) can extend tube life to about 100,000 hours.

The conclusion is that "hours of use" of course do matter for hams intending to use their 
tube-type radios for thousands of hours.  The hours of use can be limited by simply turning the 
tube off when having only stand-by function.  However, there is some suggestion in the literature 
indicating that every "turn on" of a tube (or an incandescent light bulb) involves rapid 
heating of the elements inside which could, immediately or over time, deform elements and causing 
sudden failure (given that the metal elements do heat unevenly--due to resistance in the metal--if 
only for a very short duration of time).  Repetition of on-and-off cycles are thus a factor in 
lower tube life.

Other than these factors, it appears in the literature that operating a tube, 
particularly high power transmitting tubes, at its rated values can extend life 
IF it is otherwise not sometimes operated below or above its ratings.  It 
appears that, for example, driving an RF amplifying tube at its full rated 
power does not materially decrease its life.   Reducing drive appears not to 
extend such tubes' life.

It is all a balancing act.  73, Charly

P.S., next question is "do transistors 'wear out'?"
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