[Radio Wrangler]

The brown Hunts capacitors aren't electrolytics. They aren't polarised. Inside they're just paper and metal foil, no electrolyte.

They work equally well either way round.

Some non-polarised capacitors have a marking band near one lead to say which lead connects to the outer foil. This makes a slight difference in some circuits due to stray capacitance to neighbouring components and wires. In this recorder you needn't worry, but it's good practice to see if the original component has a marking and if the replacement does, put them in the same way.

There are three groups of capacitors you need to be able to recognise:

1) Electrolytics. These are usually the largest value capacitors in a set and are mostly used as energy stores (reservoir and smoothing capacitors) and as low impedance signal coupling and decouplers for audio frequency circuits. Electrolytics can last almost forever under favourable circumstances, but heat tends to drive moisture out, drying their electrolyte so they get lossier and lossier. Electrically, they look like capacitors of reducing value, with an ever-increasing resistance in series with them. Electrolytics can degrade over years of dis-use, though many can be restored by a process called re-forming. They are the reason why long-unused equipment should be brought up gently, not plugged straight in. Replacement parts need the right voltage rating or more, and a larger capacitance is usually OK

2) General non-polarised. These are used for signal coupling, tone controls, filters and timing circuits. They aren't very critical on value. Paper or plastic films are the usual types. Paper ones take in moisture from the air and go electrically leaky. Some makes are renowned for this (EG Hunts) The electrical leakage can affect the bias on valves and cause damage much more expensive than the capacitor. Some plastic film types seem to last forever (EG Philips 'mustards') Go for the same voltage rating or more, you can often take liberties on the exact value.

3) Precision capacitors These are usually found amidst the coils and tuned circuits of radios. Most types are fairly reliable. Exact capacitance value is needed and re-alignment of the set is often needed after replacement. Stick to the same type or else you may get temperature related drift of the tuning. Generally these are left alone until it becomes certain that one has failed.

David