Crawls Backward (When Alarmed)

IconProjects, musings about guitar builds, guitar repairs, vintage tube amplifiers, old radios, travel, home renovation, and other stuff.

Restuffing Filter Capacitor Can on Rickenbacker M-8 Amp

I'm putting new filter caps into the Rickenbacker M-8 amp.  This amp uses an aluminum capacitor 'can' that has 2 capacitor sections of 40 uF at 450 volts each.

First I need to unsolder the connections going to the can's terminals.  There are terminals for each positive end of the caps (2 terminals).  The negative, or ground side, is the can itself.  The can is attached to the amp chassis with tabs that are soldered to the chassis.  You can see the blobs of solder in the picture.

I like to use solder wick to remove all the old solder from the terminals, which is what's going on in the picture.

If you've ever tried to remove one of these caps, you know you need big heat to melt the solder.

This is my 175 watt Weller iron.  Yes, that's the actual size of the iron compared to the amp chassis!  The tip's about 1/2 an inch (12mm) wide!

I've tried soldering guns and small irons together on these solder joints, and they don't work well.  You need higher wattage, because the chassis acts as a heat sink.

Here's a melted joint, still hot.  Notice how shiny it is.  You can see the mounting tab for the can now that the solder has melted away.

This chassis is pretty thin - it only took about 15 seconds to melt the solder with the iron.  Fender chassis are a lot thicker and take a bit more time.

The process is: heat the solder till it melts, then suck up the solder with a solder sucker.  It takes a few passes to get most of the solder up.

Then I use wick to get the remainder.  You can see the tab to the left of the sucker is clean.

Then we just bend the tabs back and the can will come off the chassis.

One note on the cans:  these are very common in American- and European-made gear from the mid 1950s to 1970s.  You can see why they were used - they take up less space than discrete capacitors do.  There are many different caps out there - some have up to 4 sections with different capacitance and different voltage ratings in the same can.

I like to 'restuff' the cans with new modern capacitors.  You'll see some folks just disconnect the caps from the circuit and use discrete caps in their place.  That works fine, but I don't like the look of big capacitors sitting willy-nilly in the chassis.  Restuffing keeps the original look in place, and preserves the exterior of the can.

In the past, I've used a Dremel with a grinding wheel to cut open the can.  I recently read a post on the Antique Radio Forums site where someone mentioned using a sharp kitchen knife to open the cans.  Just roll the can under the knife.

It works great.  You get a finer cut and less denting of the can.  The can is thin aluminum; it's easy to dent it.  It's also easy to cut!

Here's the can opened up.  Use gloves to remove the old innards.  Dispose of them properly.  Where I live, we have a hazardous waste dump.  I take all my old paint, batteries, etc, there, as well as this kind of refuse.

Now we need to cook up an assembly of sorts made of modern caps.  I'm using quality Panasonic capacitors for this one.  The old sections were 40 uF - the modern replacement is 47 uF.

I put shrink tubing on the two positive leads (yellow and red), and soldered together the negative leads.  I'll pass the leads through the bottom of the can and solder them to the appropriate tabs.

Here's the whole assembly going back together.

You can see how I ran the leads out to the terminals.  There was one hole in the center of the bottom of the can.  I drilled that out and passed the positive leads out and soldered them to their terminals.

The negative lead goes to one of the can tabs.

I had lightly sanded the mating surfaces on the top and bottom of the can flat, so they'd line up square.

Then I use JB Weld epoxy to attach the two sections.  The epoxy dries to a gray color.  If you're careful to get the squeeze-out, the glued seam will look like the can has never been opened.

I gently squeeze the can in a vise until it dries.  Again, the aluminum is soft, so be careful not to leave jaw marks on it.








 
 
 
 

Post a Comment 0 comments:

Post a Comment