Kathy, considering the SB200 has been around more than 40 years and yours
lasted that long without the soft start modifications, one might hope it
would continue on a few more years without them.
What is a really likely scenario is the old electrolytic capacitors have
gone bad and in need of replacement. There are a number of capacitor sources,
even on Ebay. New capacitors will not mount in the same manner as the old
ones so some ingenuity will be needed. Silicon adhesive is crude and ugly
but works well.
There are better diodes available than the originals, such as 1N5408 and
others. You can find them for around twenty five cents or so brand new at
Mouser Electronics and other sources.
There is no need for equalizing resistors and capacitors with modern diodes
so those parts can be removed. If it is easier to install new diodes on
the reverse side of the board, then no harm; the electrons don't care.
I hope it goes well with your repairs.
73,
Gerald K5GW
In a message dated 3/24/2011 11:16:49 A.M. Central Daylight Time,
wb2aio@yahoo.com writes:
I know many of you probably consider a SB200 as a driver for your real
amps, but for us QRPers, it is as good as it gets:)
I just blew a diode in HV chain. Now one friend I respect says I should
put in the Harbough board, soft start, etc. Trouble is, that's money I don't
wish to spend if I don't have to. Put in new board is easy to say when you
have money, but us poor underpaid nurses....
Taking a look at mine, I noticed there are 3 diodes already replaced in
the two strings by placing them under neath or on the bottom of the board.
When I first looked at it, I thought they had been vaporized:), so this isn't
a new problem.
I'm hoping to find something at Radio Shack I could use and just change
out the newly blown diode, maybe even using the trick the previous owner
employed of just putting in the new one underneath to save taking it apart to
get at the top of the board.
So was wondering what you guys think or your experiences with the SB200. I
just acquired it last summer and otherwise has worked really well when
I've needed it.
73,
Kathy, RN
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