Sb-301

[Bob And Bettina Groh]

Chris,

Took a quick look at the schematic and it looks like that resistor was 
feeding dc power to the last filter cap. I'll wager a guess that the 
electrolytic is bad - when they are that old, the chances are very good 
that they are bad, going bad or will go bad in short order.  Hopefully 
the 'smoke' is from an overheated (and failed) electrolytic and not a 
nuked power transformer (which failed because of a bad electrolytic). 
 If the former, you should be able to replace the cap(s) [more later] - 
if the latter, you are probably left with a parts rig as power 
transformers are hard to find.

Now to a replacement electrolytic - the old multi-section capacitors are 
available but somewhat pricey. Or maybe a lot pricey! Antique Radio 
(www.tubesandmore.com - I think) might have some. You could probably ask 
on the list for more suggestions. As a suggestion, do not buy 'nos' (new 
old stock) - not a good gamble.

Another suggestion for a replacements is to use new individual 
electrolytics (www.mouser.com is one excellent source) - you either 
disguise them inside the original capacitor case (after pulling the old 
stuff out) or just put them underneath the chassis where-ever.  Again 
some nice sources of the internet on how to do that.

The whole question of capacitor replacement was just played out here on 
the list and the general concensus was - always replace the 
electrolytics. If they haven't failed, they will soon.  So why fool 
around.  The general subject also includes the question of 'reforming' 
electrolytics and I can recommend the following web sites for information:

http://www.vintage-radio.com/projects/capacitor-reformer.shtml

http://www.angela.com/catalog/how-to/about_caps.html
Excellent overall analysis

http://www.vcomp.co.uk/tech_tips/reform_caps/reform_caps.htm
Just a replay of the angela site

http://www.nmr.mgh.harvard.edu/~reese/electrolytics/
Interesting little circuit to reform caps - I think I will try it (a 
voltage tripler).

http://www.vmars.org.uk/capacitor_reforming.htm
Looks very interesting.  

Good luck and hope it wasn't the transformer.  Chalk it all up to 
experience and keep going!

73
Bob Groh, WA2CKY



sb200 wrote:

>Hello all I picked up a SB-301 the other day the receiver was way way down and all I could hear was some AM broadcast on 40 meters.  
>
> I found that the someone of this had lifted one leg of a 330 ohm 2 watt resistor from lug 4 of the cap.  I need the 100-40-40-40 ufd electrolytic Capacitor for my Sb-301.  The part # is 25-163.  I'm not sure but I think that this resistor was lifted so the unit would light up but not burn out but I'm not sure.  I would like and try to keep it all original it's clean and I'm sure it can be brought back to life.
>
>I re soldered the resistor and it came back to life.  The audio sounded bad like it's being overloaded.  It also had low meter readings as well with stations that I know should be 40 over were S6.  
>
> I came back into the shack to find the unit off and a smoke smell in the shack.  This is what happens when the wrong fuse is used.  Any Ideas ?
>
>Maybe someone has a part rig they want to part with I may need other parts.  Thanks for the info.
>
>Chris n2uqs
>
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for losses or misrepresentations of any kind.  Buyer beware!

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