It was empirecal......................0.1uf quieted things down pretty well
to around 100kHz, 0.47uF was good down to 50kHz, so I took the next step and
went to a 1uF. Even down at 10kHz, all you hear is atmospheric
noise................no buzzing from the power supply. If you look at the
older TenTec linear supplies, you will see .1uF being used, but these
supplies were intended to be used with rigs that only tuned down to 1.8MHz.

Pete

"starman" wrote in message
...
How did you arrive at the 1uF value for the transformer caps?

Pete KE9OA wrote:

That would be good. Another thing...............the 1uF caps that bypass
each leg of the power transformer secondary to ground are even more
effective than the .01s across each diode.

Pete

"starman" wrote in message
...
I was just wondering the other day whether I had added those RF bypass
caps' when I was doing the power supply mod'. I think I replaced the
discrete OEM diodes with a four diode bridge assembly but I may have
forgot the caps'. I'll take a look.

BTW- I might be able to take a picture of the power supply mod' with a
digital camera if you'd like to see how I located the parts in the
chassis.


Pete KE9OA wrote:

That sounds like a good thing to do. An improvement you can make to
the
standard Drake power supply is to connect .01uF caps across each of
the
diodes. Also, bypass each leg of the power transformer secondary to
ground
witha 1uF NP cap. This removes that "flourescent ballast" type of
buzzing
hash that you may hear on frequencies below 700kHz. If you have the
later
unit that tunes down to 100kHz (which I wish I had), expect much
lower
noise
performance down there.

Pete

Starman wrote:

I got tired of keeping track of the wallwart for my SW8, which
doesn't
fit in the Drake carry bag. The remedy was to cut open the wall
wart
and
install the parts in the radio. I had to move the battery holder
about
an inch to one side to make room for the transformer. It was a
tight
fit. I also added a receptacle on the back which accepts a
standard
computer power cord. I probably have the only SW8 with an internal
AC
power supply.


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