Although I agree, I would modify the conclusions a bit.
High power semiconductor device technology is becoming more mature, with
the result of longer device life cycles. Also, the longer a device
remains viable the more money the device maker makes. Silicon wafers
have gone from around a half inch to an inch when I started in the
industry in 1961 to approaching 14 inches last I knew. A wafer 14 inches
in diameter has a more uniform composition in addition to an area that
yields many good devices. This reduces the cost per device greatly. This
means they can cut the price and still make a greater profit.
Starting with polycrystalline silicon out of the reactors, by the time
the device is finished over half the silicon is waste.
In the late 1960s, or into the 70s, the company I worked for implemented
a new method for sawing wafers from single crystal rods. This reduced
the loss by over 50% and basically doubled the output in just around a
week which made for a major cost reduction in price which suddenly
created a glut of silicon
and resulted in a reduction in the number of companies selling poly and
wafers. Incidentally, poly is now available right out of the reactors
in a more pure state than was available in single crystal form just a
few decades ago.
I believe the top companies are selling in the neighborhood of a
thousand metric tons of poly each.
So it's likely the new devices we see today may be in production twice
as long (or longer) than earlier devices.
One of the problems ham gear faces are the use of small production runs
using specific devices to save a few dollars, meaning replacement
devices may not be available for long.
The current crop of new devices is likely to be around much longer than
devices made just 10 years ago.
OTOH as W8HW said, the input of the high power devices is extremely
fragile. Over drive and spikes of very short (few Ms) duration that
wouldn't faze a tube can be fatal for SS devices.
OTOH, there is little danger of transistors setting on the shelf for
long periods going bad, unlike tubes with glass to metal seals.
I do think SS amps, or SS top end amps will replace the equivalent tube
amps in around a decade
73, Roger (K8RI)
On 6/4/2017 Sunday 12:29 PM, w8hw@comcast.net wrote:
Hello Jim and group,
I respectfully disagree. Tube amps are not a thing of the past nor will they be
for a long time to come. I would like to point out that I own and use both
Solid state and Tube amps and love them both. Each has its advantage. You did a
great job pointing out the advantages of solid state, I would like balance the
issue by point out the advantages of Tubes.
Obsolescence is been very poor for solid State transistors for both high and medium power
amplifiers. AS a person that repairs amplifiers (both solid state and tube) for others has
(since 1972) been forced to deal with issues like that. A solid state device that is in vogue
today is likely to be “History” in short 2-4 years or so. Replacement
transistors are another disappointment. As an example Icom 706 MK2g was still selling the
radio when the final transistor became unavailable. A replacement transistor involved
modifying the printed circuit board and to do that required transplanting components to
another place. Tubes on the other hand like 8877 and 3-500 and others, enjoy a long history
of 40 + years and have no end in site. so that makes the Tube amplifier easer to get repaired.
Another disadvantage of LDMOS is the input side of the LDMOS has a “Glass Jaw”.
If you over drive them it can be a quick death, while a tube will take an occasional over
drive.
Amplifier Life and longevity is strongly on the side of the tube amplifier. If you want it to
last 25 to 40 Years. Do not put all of you eggs into a solid state amplifier because in 3-5
years you may be faced with owing a “door stopper” and looking to buy another
amplifier. I consider this a very serious issue. In fact I consider the ability to repair to
be the most important issue for hams that can not buy multiple amplifiers.
Thanks, Bruce, W8HW
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