Sparton Equasonne Radios

Rebuilding cathode bypass capacitors in the RF amplifier unit of the Sparton Equasonne

The original paper capacitors in the Sparton Equasonne are rather primitive and poorly built.  They were highly prone to electrical shorts.  If they are still present within your set, they are definitely due for replacement!  The factory originals consist of a brass center post wrapped with metal foil and paper and covered with a layer of black paper.  One end of the capacitor electrically connects to the brass center post. This post is connected to the circuit board via a small screw which threads into the exposed end on the bottom surface of the capacitor.  The other end of the capacitor is electrically connected to a small metal tab which projects from the bottom edge of the capacitor.  This tab is physically connected to the circuit board either by a screw or by a solder joint.  Sadly (happily?) exact replacements are no longer available.  Perhaps some or all of yours have already been replaced untold ages ago with ugly and also substandard replacements which are probably crudely shoe-horned into place.  These replacements may themselves be in need of replacing.  The following is a method to create replacements that very closely resemble the originals.  If the originals are present, they can be disassembled and some of the original parts used in the construction of replacements.  If the originals are missing it should still be possible to create replacements similar to those described below by obtaining reasonable facsimiles of parts A, B and C from a hardware store.

Rebuilding

The original paper capacitors in the Sparton Equasonne are rather primitive and poorly built.  They were highly prone to electrical shorts.  If they are still present within your set, they are definitely due for replacement!  The factory originals consist of a brass center post wrapped with metal foil and paper and covered with black paper.  One end of the capacitor electrically connects to the brass center post. This post is connected to the circuit board via a small screw which threads into the exposed end on the bottom surface of the capacitor.  The other end of the capacitor is electrically connected to a small metal tab which projects from the bottom edge of the capacitor.  This tab is physically connected to the circuit board either by a screw or by a solder joint.  Sadly (happily?) exact replacements are no longer available.  Perhaps some or all of yours have already been replaced untold ages ago with ugly and also substandard replacements which are probably crudely shoe-horned into place.  These replacements may themselves be in need of replacing.  The following is a method to create replacements that very closely resemble the originals.  If the originals are present, they can be disassembled and some of the original parts used in the construction of replacements.  If the originals are missing it should still be possible to create replacements similar to those described below by obtaining reasonable facsimiles of parts A, B and C from a hardware store.

 

Parts

1uF paper capacitor (one of 4) from the RF amplifier unit of a Sparton Equasonne radio disassembled and ready for rebuilding.  The black paper cover and the paper and foil windings have been removed by unwinding and/or or by cutting with a razor blade.  The brass center post (A), with the wax-coated top piece, the bottom circular electrode (B), and a mounting screw (C) are all that remain of the original capacitor.  A wooden dowel (27 mm or 1 and 1/16 inch) diam. (E) is used as a form to create the outer tube for the rebuilt capacitor (D) shown at the top center of the picture.  A small slice (F) has been cut off the same dowel to serve as a base for the modern polypropylene capacitors  (yellow), figure (G) in picture.

 

Cutting out bases

Slices are cut off the wooden dowel to make bases (and tops) for the new capacitor.  Cut the slices about 2-3mm thick, and cut a fair number of them, they are prone to break while drilling.  Slices used for the base need to modified to resemble (F) in previous figure.  Cut a small notch in the side to accommodate the tab on the circular electrode (see (B) in previous figure) and drill a center hole large enough to accommodate the brass center post.

It is actually easier to drill a hole into the dowel first, and cut a groove to serve as the notch before cutting off the slices.

 

Modifying the original capacitor


Because the polypropylene capacitor is too big to squeeze inside the old capacitor with the brass center post intact, the post must be sawn up to make room.  Cut off and retain the top end of the post with the wax top piece, and cut off the bottom threaded end.   The bottom end will be used as a mounting post for the new capacitor and will be soldered to one of the new capacitors lead wires.  The upper end of the stub has been cut and filed to form a tab, and a hole has been drilled in it to accept the capacitor lead wire (see line drawing).  On some of these old capacitors the top does not consist of a wax plug, rather it is made from a black metal washer, which is attached to the top of the brass center post by a screw. In this case, retain a large enough chunk of the top of the center pole to accommodate the washer and screw.

 The donut shaped bottom electrode (with tab) will attach to the other capacitor lead wire.  The electrode has been cut and one end bent up and drilled to create a tab to attach this wire.  This is visible in the above photo.

 

Clean the sawed-off brass mounting stub (line drawing) with brass polish or steel wool.  This will enable you to make a good solder connection.  Feed the lead wire from one end of the capacitor through the hole drilled in the top of the stub and wrap it around the stub a few times.  Solder the connection (see below).

 

Internal parts

Solder a short lead wire to the circular electrode (picture on left).  Cover the joint of this lead wire with shrink tubing and either shrink tube or paint the base of the capacitor stub with liquid electrical tape to prevent shorting of these two components when assembled.  The capacitor itself is soldered to the metal stub (picture on right), and the joint painted with liquid electrical tape (picture on left).

 

Assembling the capacitor

Epoxy glue the circular metal electrode to the wooden base, making sure it is well centered with the hole drilled through the center of the wooden base.  When dry, Insert the brass center post with the attached capacitor into the center hole of the wooden base.  Make sure you have used shrink tubing or liquid electrical tape (or both) on the brass post to prevent it from shorting to the circular electrode.  This is very important as the round metal electrode and center post come in very close proximity to each other.  Glue the capacitor in place with more epoxy cement. 

Solder the short lead in wire from the circular electrode to the lead on the top end of the capacitor.

To ensure you have created no electrical shorts between the two electrodes, connect an ohmmeter between the side tab and the threaded center hole on the underside of the wooden base.  You should measure infinite resistance between these points.  If so, continue with reassembly.

Making a cardboard tube

Cut a strip of brown paper 53 mm wide and about 40 cm long.  Angle the edges as shown.  Cut a similar strip of black construction paper 53 mm wide and about 20 cm long.  The capacitor body you will create with this paper will be 53 mm tall.  This is slightly taller than the original capacitors (approx 50 mm) used in the Equasonne, but will allow you sufficient room to make all the internal connections.  If you wish, you can manufacture the tubes to be slightly taller (up to about 60 mm) to allow extra room.  Do not make them any taller than 60 mm.  As the 485 tubes flare out towards the top, there is no room to accommodate a capacitor this wide which is taller than 60 mm.

 Wrap the brown paper strip around the wooden dowel.  Use glue to form a tube (see photo on right).  Be careful not to glue the paper to the dowel!

 

Final assembly

When dry, slip the cardboard tube over the capacitor and around the wooden base.  It should fit perfectly.  The tube is glued to the base with white paper glue.  The glue is applied to the inside perimeter of the tube before slipping it around the capacitor and base.

There should be a small amount of space at the top end of the tube.  Slide a wooden disk cut from the dowel down the tube so that it rests on the top of the internal capacitor.  This will make the unit a bit sturdier.  Glue the disk in place with white paper glue.  The original wax end cap can then be glued in place on top of this.  If this wax disk broke during the disassembly of the old capacitor (more than likely), either glue it back together, or make a new one.  Do not actually use wax, as the heat of the tubes will melt it during operation.  A mixture of 5-minute epoxy and brown or black paint makes a durable and convincing replacement.

As mentioned above, some of these capacitors were not sealed on the top with wax, but with a metal washer.  This washer is attached to the brass center post by a screw.  If your capacitors use the metal washer, drill a hole in the top wooden dowel slice to accommodate the upper end of the brass center post that you previously sawed off and retained.  Insert and glue this center post to the wood slice, leaving the threaded upper end flush with the wood surface.  Place the metal washer on this and screw it into place with the original mounting screw.  Insert and glue this unit inside the top of the cardboard capacitor tube.

 Wrap and glue the black paper strip around the capacitor and voila!  You have a replacement capacitor ready to install that not only meets, but vastly exceeds the specifications of the original.

 

Rebuilding the 0.2uF paper capacitors located underneath the RF amplifier circuit board.

The original 0.2uF paper capacitors in the Sparton Equasonne may still be functional, but are unlikely to still be working well or to be trustworthy. They are so cheaply and easily replaced that it is well worth your while to do so.  The two capacitors sit end to end in a metal holder mounted underneath the RF amplifer circuit board.  The lead wires of the two adjacent ends are tied together and grounded through a solder joint to the metal holder itself.  The opposite ends of each capacitor are joined to circuits 3 and 4 (which power the heater filaments of the 484/485 tubes and the dial lamp.

You could simply just remove and discard the originals and replace them with 0.22uF 630volt metalized polyproplylene caps (available from Antique Electronic Supply and elsewhere).  These caps are approximately the same size and shape as the originals.  Alternatively you could drill a hole through the center of each of the originals, to convert them into hollow tubes, and place the slightly narrower replacements inside.  As this is so simple to do, it is the technique described below.

 

How it is done

An original Sparton 0.2uF paper capacitor is shown in figure A.  The original leads were made of braided copper wire and were clipped close to the capacitor itself leaving them attached to the circuit board for use in mounting the replacements.

A hole is drilled through the center of the capacitor (B), starting with a small drill bit and then progressing stepwise through larger bits until a tube is formed that is wide enough to accomodate the modern replacement (C).  As you progress to larger bits, it is actually easier, safer, and faster  to insert and turn the drill bit by hand, to ream out the hole, rather than actually using a drill.


Once a large enough hole has been bored, the replacement capacitor can be slipped inside the outer shell of the original and glued into place with a small amount of epoxy glue (D).

Once the glue has dried, coat the base of each lead wire with liquid electrical tape.  Allow this to dry.  Fill up the end of each capacitor with silver or black silicone sealant to complete the deception! Alternatively, fill the ends with epoxy glue, and then paint the ends silver when dry.

Remount your rebuilt capacitors in the holder under the RF amplifier circuit board, and you are done.  The board shown on the right has restuffed capacitors, and you cannot tell.

 

 

Rebuilding electrolytic filter capacitor in the power supply (Not in all models)

Some later model equasonnes featured a dual section wet electrolytic filter capacitor in the power supply.  These capacitors are located in a round can on the power supply module, which is either painted black or gold.  This can capacitor can be opened, new modern capacitors installed inside, and then resealed.  The repair is invisible once accomplished.

Photos used in this section were kindly provided by Jeff Codori from his restoration of a Model 589 Equasonne.

Removing the capacitor from the chassis

The can capacitor is held on the chassis by friction only, however it is usually held on quite tight.  The can itself forms the negative connection of the dual capacitor unit to the chassis of the radio.  First remove the tubes from the radio, then remove the metal lid from capacitor.  This uncovers a pair of terminals with lead wires attached.  Unbolt the two lead wires from the capacitor.  They will be reattached to the terminals once the capacitor is rebuilt.  Next remove the power supply chassis from the wooden shelf, turn it upside down.  It is possible to remove the capacitor from the chassis by pounding it out  with a mallet, but it is difficult, and you will significantly scuff the capacitor up.  It is actually easier to leave it in place and operate on it while it is still attached to the chassis.

Opening the can

The upper surface of the capacitor, where the two terminals are located, is made of a black phenolic material.  A rubber gasket around the edge of this makes a water tight seal.  To remove this phenolic lid, use a a drill.  Perforate the edge of the phenolic lid all the way around the can.  The lid can then be pulled out of the can as shown in the photo to the left.  The can is full of liquid, be careful not to spill it.

 

 

 

Once the lid has been separated from the rest of the can, pull the lid away.  The two capacitor plates will come out of the can with the lid.  cut these off, they are no longer required.

 

 

 

 

Installing new terminals

 

 

 

 

 

 

 

 The positive leads of the new capacitors will be attached to the terminals on the phenolic lid.  The negative lead wires of the two capacitors will be joined together and then attached to the inside wall of the can.

First, remove the old mounting terminals from the lid, they will probably be loose.  New terminals can

 be fashinoned from bolts by cutting of the head of the bolt.  Install the terminals on the phenolic lid by using epoxy glue. Sometimes the old lid is warped and damaged, so that it is not really reusable. In this case a new lid can be fashioned out of a small piece of 1/4" black garolite if you have access to a scroll saw and a sander.  

 

Installing the new capacitors

 

Lugs can be soldered to the positive leads of the new capacitors.  This will make it easy to attach them to the mounting terminals.

The negative leads of the two capacitors should be soldered together.

The capacitors can now be bolted to the underside of the phenolic lid. The negative leads need to be soldered to the inside wall of the can.  First clean the inside of the can with steel wool to make it shiny.  A very hot soldering iron is required for this task.  Solder a long lead wire to the inside of the can first, make sure the wire is long enough to project out of the top of the can. You need a pretty significant soldering iron to pull this job off. An alternative is to drill a small hole in the bottom of the can, and then attach a lead wire with a ring terminal and a screw.

Next, epoxy glue some styrofoam blocks to the inside wall of the can.  The upper edges of the blocks will be used to support the phenolic lid when it is placed back in the can.

Cut out a round styrofoam gasket to fit on top of the styrofoam blocks.  Make sure there is a hole in the gasket to allow you to insert the capacitor block.  Epoxy glue the styrofoam gasket into the can. 

When installing both the styrofoam blocks and the gasket, make sure you set the height so that the phenolic cap sits at the appropriate level when reinstalled in the can.

 

Resealing the can

Once the foam supports are glued in place, the negative lead wire can be soldered to the capacitor pack.  The capacitors are then lowered into the can, and the phenolic cap is seated on the styrofoam gasket.

 Use epoxy glue to fasten the phenolic cap to the styrofoam gasket.

The space around the edge of the phenolic cap can either be filled in with epoxy glue mixed with a bit of black paint, or black silicone sealant.  The latter will recreate the look of the original rubber gasket.  If epoxy glue is used, the foam gasket under the phenolic cap prevents the glue dripping into the can before it has set.  The epoxy glue can be sanded and buffed with #0000 steel wool when dry and it will be difficult to distinguish it from the black phenolic cap.

Once dry, the entire can capacitor can be replaced in the chassis, using a wooden block and a hammer.  Pound the can into the mounting hole until it is tightly seated.  The original lead wires can then be rebolted to the new terminals, and the metal lid reinstalled.  The repair is totally invisible.

 

 Repairing a Magnavox Speaker.

This Magnavox speaker was common to several Equasonne models including the 301, 930 and 931. The speaker surround was made of small thin leather strips which often are found to be dried out and crumbled. In many cases the cone itself is still in good shape, although it is not too difficult to make a new one out of thick black paper if it is damaged.

Step 1: Remove the screws around the outer lip of the speaker that hold the metal bezel onto the edge of the speaker surround.

Step 2: Remove the two screws that hold the spider. This is a bit difficult as the screws are recessed inside the housing. A sideways screwdriver may help, or try hold putting the screwdriver blade in the screw slot sideways. The screws are probably not in all that tight. Be careful not to damage the cone, voice coil or spider, which can happen if your screwdriver slips.

 Step 3: Unsolder the two lead wires to the speaker voice coil.

Step 4: Using a straight edge razor blade remove the metal bezel from the speaker housing. Scrape away all remaining traces of the leather surround, and clean up the surfaces with #0000 steel wool.

 

Step 5: Using a straight edge razor blade scrape all traces of the old leather speaker surround off the edge of the cone. This will crumble off the surface quite easily.

 

Step 6: Obtain a new speaker surround. These can be bought from Mat Electronics. You want the 12” size. http://matelectronics.com/speaker-replacement-parts/383-fer-12.html  The only issue with this supplier is that they have a minimum order of $25, so peruse their site for other stuff you might want, or buy a lifetime supply of speaker surrounds. If you can't find $25 worth of stuff, email me, I normally have some of these lying around.  You could in principle use small leather strips like the original instead of a modern foam surround, but I have never been able to find any leather nearly as thin and flexible as the original. The replacement speaker cones at Mat Electronics are unfortunately the wrong depth to use to replace a damaged cone in an Equasonne. If the cone is badly damaged, you can carefully cut the voice coil off the bottom and fold up a new cone using stiff black paper. Glue the voice coil onto the new cone, taking care to get it on exactly straight, and then carry on.

 

Step 7: The 12” speaker surround is a bit too big, but the 10” size is a bit too small. Cut the surround open, and remove about a 1” section to make it the appropriate size. This leaves a bit of extra for an overlap to allow it to be glued back together.

 

Step 8: Paint the edge of the speaker cone and the edge of the speaker surround with Pliobond cement.

Step 9: Position the speaker cone on the foam surround. The glue is a type of contact cement so you don’t have a lot of opportunity to reposition it once the surfaces touch. Sit the cone face down as show while it dries so that you can observe the angle it makes so you can be sure it will go back on straight.

Step 10: Seat the speaker back in the housing. Replace the two spider screws and resolder the two voice coil lead wires.

 

Step 11: using a hot soldering iron, melt holes in the foam surround for the bezel screws using the screw holes as a guide.

Step  12: Reinstall the metal bezel