Sparton Equasonne Radios

Positioning tubes in the RF AMplifier

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Capacitors

Capacitors found in the Sparton Equasonne are of several types.  In later models, the large capacitance used in power supply filter circuit were big cylindrical metal cans which were primitive electrolytic capacitors.  The filter capacitors of older models were multi-unit paper and foil capacitors housed together in large rectangular metal boxes.   Several paper and foil capacitors are used in the RF Amplifier of all models, both above and below the circuit board.  In models with an additional tube in the selector unit, a paper capacitor is also used as a cathode bypass.  Paper and electrolytic capacitors do not age well and will need replacing.  Modern replacements look nothing like the originals and are also much smaller.  There are also several small value (picofarad range) capacitors found in the RF amplifier.  These tend to be much more durable than paper or electrolytic capacitors, and may still work fine.

There are three strategies for replacing capacitors.

1) Remove and discard the entire original and wire in the replacement.  This is generally the least satisfactory method as modern replacements look so different and are so much smaller, you will leave gaping holes in the chassis of your radio.  Not only will your  radio end up looking strange and ugly, but this probably will detracts from its value.  This would be an OK approach to replacing the two 0.2uF paper capacitors located underneath the RF amplifier circuit board.  Modern replacements are the same shape and only slightly smaller, also these capacitors are only visible with the amplifier unit disassembled.

2) In principle, the originals can be left standing in place, so long as they are electrically disconnected from the circuit.  It is often possible to wire in the replacements under the chassis or circuit board where they are hidden from view, or at least inconspicuous.  This is perhaps the simplest solution, as it does not require a lot of extra effort, and also does not disfigure your antique radio.

3) Some people prefer to take advantage of the fact that modern capacitors are very much smaller than the originals.  With some amount of extra effort, the originals can be opened up or hollowed out and the modern replacement physically installed and hidden in their interiors.  This method will keep your radio in as close to its original state as can reasonably be achieved, while allowing it to work properly.  I took this approach with my three Equasonnes just for the additional challenge.  Detailed instructions for doing this are found elsewhere on this website.

Replacement capacitors should be close to the capacitance of the originals, or slightly bigger.  As well as a capacitance, capacitors also have a voltage rating, which indicates the maximum voltage to which they should be exposed.  Replacements should be rated at least as high and preferably higher than the originals.  As the voltage ratings of the originals is often not known, it is best to err on the side of caution.

There are several suppliers of capacitors specifically for the resotration of antique radios on the internet: Bob's Antique Radios, or Antique Electronic SupplyJustRadiosto name but three. Radioshack does not carry capacitors rated for the high voltages found inside the Equasonne, in fact most electronic shops do not.  

Do not buy capacitors that are NOS (New old stock), as capacitors deteriorate with age, even when unused.  

The four large black paper caps in the RF Amplifier of all Equasonnes (3x 1uF and 1x 0.25uF) can all be replaced with 1uF 630V replacements.  See the RF Amplifier page for details.

The exact values of the filter caps in the power convertor vary between models.  There seem to have been at least 4 different models of multiunit filter capacitor used in the various Equasonne models.  The nature of replacements for these will be discussed under the notes for each model.

The pair of 0.2uF paper capacitors located under the RF Amplifier circuit board can be replaced with 0.22uF 630V polypropylene caps. These caps are
roughly the same size and shape as the originals.

Mica and/or ceramic capacitors were used in the RF Amplifier unit to obtain smaller capacitances (nanofarad to picofarad range).  These generally age well and do not need replacing.

Technically speaking, the giant tuning condenser in your radio (big thing with rows of brass fins) is a variable capacitor.  It is pretty durable and should not need replacing.  In parallel with each of the 4 ganged sections of this tuning capacitor are small mica trimming capacitors to fine tune each circuit.  Unless these are physically damaged, they also should not require replacing.