Astron “Minimite” electrolytic capacitors were ubiquitous in early Fender (and other) amplifiers. The brownish-orange caps were used as filter capacitors, cathode bypass caps, bias caps, and etc.
Most of these capacitors are now 50+ years old, and should be replaced. Actually, they should have been replaced 30 years ago. It speaks to the high quality of the Minimites that some of them are still in use in the old classic amps.
Most often, the Astron Minimites are cut out of the circuit and replaced with new capacitors like Sprague Atoms or Nichicon or IC, or other modern manufacturers.
It is possible, however, to restore Astron Minimites in a way that retains the original classic look of the capacitors. This is a step-by-step tutorial that describes a fairly easy way to make “new” Astron Minimites.
STEP ONE
The Minimite capacitors must be removed from the circuit. Do not just cut the exposed wires – remove the capacitor leads from the circuit board eyelets with a quality soldering iron. In the photo, there are four 20 uF Astron Minimites that are the filter capacitors of a 1958 Fender Tremolux. Note that the negative leads are soldered directly to the metal capacitor cover; all four of the negative leads must be de-soldered in order to remove the caps. The positive leads have already been de-soldered.
STEP TWO
The Astron Minimites of this era had a cardboard outer shell. We are going to remove the actual capacitor from the shell, and replace it with a new capacitor.
The best way to remove the shell is to use the end of a small, cheap paintbrush to undo the crimp on the positive side of the cap. Any improvised tool will work, as long as it is somewhat flexible and blunt on the end.
Push your improvised tool under the crimp, and then work it around the circumference, unrolling the crimp as you go. Take your time and be careful not to tear the cardboard shell.
STEP THREE
With the cardboard shell un-crimped, use needle-nosed pliers to grab the positive lead of the metal can and pull it out of the shell.
The metal can should slide out fairly easily with a strong, even motion.
If the positive lead is missing, or too short to grasp with the pliers, it is possible to push on the negative end of the can and slide it out that way.
STEP FOUR
Using a tubing cutter, cut the metal can about half an inch from the negative end. You can now pull the insides out of the can.
You will have to cut the metal foil attached to the negative end.
The waxy foil core of the capacitor smells and is messy to work with, but it is just boric acid and ethylene glycol. You may want to wear gloves. Wash your hands.
Throw away the guts of the capacitor.
STEP FIVE
Peel back the aluminum can as shown, until the positive end is also about ½ inch long.
Clean the insides of both ends of the capacitor.
Cut both positive and negative leads flush with the can.
STEP SIX
Drill a small hole near the center of both ends of the capacitor can.
STEP SEVEN
Now we can assemble the new capacitor. Put the prepared can ends on the new capacitor (an F&T in this example). Make sure the positive lead goes through the positive can end – it has a grooved end, the right side in the image. The two metal can ends must not touch each other! Notice the wide gap in the photo.
Now carefully insert the assembly into the old shell, negative end first.
STEP EIGHT
Once the new capacitor assembly is fully inserted, re-crimp the positive end of the cardboard sleeve (use needle-nosed pliers). Take your time and make it look neat. You can paint the crimp with Zinser’s amber shellac to match the color of the cardboard sleeve.
Now solder the new /old capacitors back into the circuit.
STEP NINE
All four of the Astron Minimites in this Fender Tremolux circuit are restored / new capacitors.
They look just as they did in 1958.