[AMRadio] SX101A

bbruhns at erols.com bbruhns at erols.com
Fri Nov 6 15:25:11 EST 2009

Hi Phil,

I have reformed old electrolytic caps that had lost it from long storage and disuse. It is no old wives tale, it is real.

But in addition to the electrolytic caps, don't forget to dry out the power transformer and any high voltage filter chokes before applying AC power.  Dry heat is the way to go.  Maybe hit it with a space heater for a day or two.  Don't melt it, just make it hot, and let it bake out any moisture in the big iron windings before applying AC power.

As for re-forming the electrolytic caps - do that at another time, not while you are drying the transformer and choke. You don't want the caps to be hot while you re-form them, because they generate heat in the forming process, and the danger is that they will boil their electrolyte and explode like really big popcorn.

Seems to me that it is best to disconnect the HV power, insert high voltage from some supply with the right voltage, through a resistor of maybe 47K, and watch the voltage on the radio side gradually rise as the caps re-form.  Leave the tube filaments off in the radio, so the circuitry does not load down the trickle current that is charging and forming the capacitors.

Give it some hours - maybe a day - to re-form.  The circuit loads will prevent a full charge with 47K in series, so either use a higher voltage external supply or lower the resistor value as you go.  When the voltage gets up to about 90% to 95% of normal operating levels, you can try plugging in the radio normally, just unplug it after a few minutes and make sure the electrolytic caps are not getting hot.  Then I think it is best to use the radio for one minute, turn it off and let it rest for maybe 10 minutes, use it for 5 minutes, turn it off for 10 minutes, turn it on for a half hour, turn it off for 15 minutes, turn it on for an hour, off for half hour (these are approximate times), and then just use it normally.  But if it starts humming angrily at any point, turn it off and check for hot capacitors.

Sometimes an electrolytic cap will not re-form.  The radio will hum, maybe the capacitor will load the supply heavily, and you will simply have to replace it.  But in my experience this is rare, so you should go ahead and re-form what you have.

   Bacon, WA3WDR
Sent from my Verizon Wireless BlackBerry

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