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Author Topic: SB-200 Electrolytics Revisited  (Read 655 times)
WD8PHW
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Posts: 73




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« on: August 31, 2005, 05:48:15 AM »

I'm back to restoring an SB-200, and I'm looking for replacement electrolytics. I do not want to drill holes to accommodate current capacitor styles. Has anyone installed new style electrolytics in an SB-200 without drilling holes in the power supply board? If so - how did you accomplish this? Also, does anyone have a source for new caps. that would not require any modifications to the supply board? I've searched the internet - until I've turned blue - and haven't found any.

Thanks and 73,

Greg
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K0BG
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« Reply #1 on: August 31, 2005, 07:44:14 AM »

If you do a search on this forum, you'll find at least two suppliers of direct replacements for these caps.

Alan, KØBG
www.k0bg.com
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KA5N
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« Reply #2 on: September 01, 2005, 04:50:54 AM »

One solution is to use caps with axial leads (wires comming out the ends) standing upright.  Be sure to insulate the lead that is folded back.  If the supplied leads are too short splice with bare wire or use insulated wire for the trip around.  Make sure none of the leads short from one cap to another.  The negative lead should be next to the PCB.
Allen
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WD8PHW
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« Reply #3 on: September 01, 2005, 06:52:45 AM »

Allen,

That's a great idea. Now I need to find them.

73,

Greg
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WA1RNE
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Posts: 823




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« Reply #4 on: September 01, 2005, 09:39:42 AM »

  Just curious, is the plate supply actually running low?


 If it is, it may be caused by something easier to correct, like low line voltage.


 With a nominal line input, say 230-240 vac, the SB-200 plate supply runs at approx. 2400 vdc.


 Under full load, 500 milliamps, the load regulation characteristics of the supply can result in ~15% drop or about 2000 vdc - still right on the money @ 1KW CW input, as designed. (1200 watts PEP input on SSB by taking advantage of peak power characteristics of the supply.)


 However, if the line voltage is 5-10% lower than nominal, say 216-228 vac, you'll end up with less power input - like 850-900 watts or so.


 Running the amp on 117 vac can make this worse, as the line input current is double that when running 240 vac, etc. and so will the IR drop across the line.



 If the plate supply is within nominal limits, I wouldn't bother replacing the caps......


 73,  Chris
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WA9SVD
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Posts: 2201




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« Reply #5 on: September 01, 2005, 09:40:16 AM »

Allen had some good suggestions; new (equivalent) caps will almost always be a smaller size due to better design, but be sure (as he noted) that the leads are well insulated form the top of a capacitor.
    While "direct replacement" caps may be available, if they are NOS (New old stock; a better term might be "unused old stock!") they ARE still old, roughly the same age as the caps you are replacing.  Even if never used, they still might not last long once put into service. The older designs sometimes DO dry out or otherwise degrade over time, even if never used.
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WA9SVD
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« Reply #6 on: September 01, 2005, 09:46:30 AM »

BTW, if you ARE replacing the caps in the SB-200 (or any older vintage equipment) and replace the caps, (especially if the values are slightly different than the originals) I would strongly suggest you also consider replacing the equalizing resistors across those caps.  (And possibly the bleeder resistor, if seperate from the equalizing resistors.) With age, resistors can and do change value.  For a few dollars more, it's cheap insurance to protect yourself, the equipment, AND the new caps you are installing.
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KA5N
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« Reply #7 on: September 01, 2005, 10:47:05 AM »

There are a number of web sites for restoring the SB-200.  Rich Measures has a good one.  One can replace the equalization resistors, install higher voltage and current silicon rectifiers, install a soft key and a soft start circuit, improve the meter high voltage divider string, etc. etc.  So how far one goes in restoration is up to the restorer.  Most of the mods don't cost very much and are worthwhile.
You pays your money and you makes your choice.  YMMV
Allen
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W9GB
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Posts: 2599




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« Reply #8 on: October 16, 2005, 08:22:24 AM »

For electrolytic capacitor replacement, CDE/Mallory (US mfg. in the Carolinas) has an extensive web site.
http://www.cde.com/
Mouser is a distributor/Dealer
Harbach also sells CDE for amplfiiers
http://www.harbachelectronics.com/reference/harpg5cart.htm

Sprague/Vishay
http://www.4starelectronics.com/manufacturers/Sprague_Capacitors.html

Panasonic (Snap-in & Screw tops)
http://www.panasonic.com/industrial/components/pdf/linecard_large_can_lytic.pdf
http://www.panasonic.com/industrial/components/pdf/largecan_dimensions_0701.pdf
http://www.panasonic.com/industrial/components/capacitive/cap_lcanelec.htm

To meet you criteria -- match the diameter for your replacement -- most new capacitors are actually SHORTER than the originals you are replacing in your Heathkit.

Why not just changout the entire board - with a Harbach Electronics replacement? Like the PW-202
http://www.harbachelectronics.com/reference/harpg2cart.htm
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