Thanks for that Terry.
I was recently in the market for a new power supply and straight off thought
of one of the lightweight portable switchmode power supplies.
Thank goodness my good friend Guy Atkins warned me off them, as you do now,
so I bought instead a high quality linear (old fashioned) power supply that
is doing sterling service here in this QTH right now.

Powered up with this I got a nice catch yesterday morning at sunrise
(0500) - WTOP, Washington DC, 1500
Khz, 8,000 miles from here.
Have not logged a U.S. station on 1500 Khz before (from any location), so
was quite thrilled with this new catch. The U.S. stations come in so rarely
here over the mountains that it is quite an occasion. Had the opportunity to
fiddle with the Icom 756 a bit, and found that I probably would not have
been
able to ID and record this weak catch without the 756's outstanding NR
facility.

--
John Plimmer, Montagu, Western Cape Province, South Africa
South 33 d 47 m 32 s, East 20 d 07 m 32 s
Icom IC-756 PRO III with MW mods
RX Drake R8B, SW8 & ERGO software
Sony 7600D GE SRIII
BW XCR 30, Braun T1000, Sangean 818 & 803A.
Hallicrafters SX-100, Eddystone 940
GE circa 50's radiogram
Antenna's RF Systems DX 1 Pro, Datong AD-270
Kiwa MW Loop
http://www.dxing.info/about/dxers/plimmer.dx

wrote in message
oups.com...
Switching power supplies, AKA switch mode power supplies, suck.
The active switch device is certain to fail at some point. I have
lenear
supplies that are 30+ years old, and except for replacing the filter
caps
caps at 15~20 year intervals will work until lightning gets them.

I had to attend a school on repairing switchmodes and the Sony techs
warned us that they are very sensitive to even minor changes in device
parameters. Gain,leakage everthing changes wth age and that is not
good.
As to repair, the replacement active devices must match exactly. Their
advice was repair was difficult and the repaired supply would never
be as trustworthy as a new one. They also showed us how the switching
transitor junction acts radiates ultrasonics that will eventually cause
the
junction to fail. They had a nifty ultrasonic transducer that
downconverted "audio" up to several MHz to down to 50~10,000Hz audio. I
owned a JBL professional audio amp with a switchmode that would eat
swithcing power transistors every couple of months. I got a friend to
mill the head off the
transisotr case and the junction was shattered like glass. We
sacrifcied a new transistor and the junction looked like those in a
text book.

Management insisted that we repair the switchmode supplies and sure
enough, no matter what parts we changed, they all failed in less then a

year. Part of the problem was we had no way to pick truely matched
parts.
Thjose little dabs of color on the parts show oddites like turn on/turn
off time etc. Diode turn on had to match transistor turn on etc.
A big goat rope and lots of fun.

Switchmodes are dirty as hell, and any attempt to round those nice
harmonic generating square waves only made them run hotter and fail
sooner. Some of the low noise equipemnt has the switchers in double
shielded cases with fancy feed throughs for power.
And they are still dirtier then a good linear supply.

Terry