[Amps] SB 200 blown diodes in power supply

[Vic K2VCO]

Replacing just one diode is asking for trouble. Unmatched diodes are much more likely to 
blow. I suggest that you order 1N5408 diodes online (you won't find them at Radio Shack). 
You can get them for as little as $0.15 each at Mouser Electronics (see
<http://www.mouser.com/Search/Refine.aspx?Keyword=1n5408>. You will also have to pay a few 
bucks shipping.

The original ones are 600 piv and the 1N5408s are 1000 piv. There are 8 diodes in each 
string for a total of 4800 piv, so you can use 5 1N5408's in each string, for a total of 
10 diodes.

I suggest that you also use an ohmmeter to check from the HV to ground for shorts just in 
case something else caused the diodes to blow.

On 3/24/2011 8:46 AM, Kathy Bookmiller wrote:
> 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
>

-- 
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/