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Clarification on miniature
tuning capacitors

The listing of the miniature variable tuning capacitors (eg, Jaycar RV-5728) as having a range of 60-160pF may be confusing to some constructors. The capacitance range in practice of the oscillator stage is usually about 9-65pF and the aerial stage is about 9-146pF.

When connected in parallel, the total range is usually about 18-216pF, as measured with a Lutron LCR-9073 meter.

Matthew Weatherley, VK4TMW,
Highfields, Qld.

Reliability of
electrolytic capacitors

I have been servicing commercial lighting and communications products for several years and have noticed a dramatic increase in failure of electrolytic capacitors in the power supply stages and other parts of the circuits.

In the past decade, capacitor failures were due largely to manufacturers’ use of “cheap brand” units or the use of lower temperature capacitors than required. However, in recent years, where they are using known-quality Japanese high-temperature capacitors, they are still failing after only one or two years (just out of warranty). Previously we would get typically 6-10 years service life before the capacitors were failing.

I am starting to suspect that the capacitors now coming out of China and the cost-cutting demands have lead to the supply of a poor-quality product with the same brand names across the range. It used to be that you could rely on certain brands as being a quality part but not anymore.

I was just wondering if other service companies are noticing a marked increase in electrolytic capacitor fail-
ure.

Peter Bates
Hillcrest, Qld.

Comment: there does appear to be a downward trend in reliability of electronics products, especially where high-power switchmode circuitry is employed. The high-frequency ripple and switching currents in these devices, combined with the high-density of components on PC boards and insufficient ventilation, are all significant factors.

However, we cannot comment on the basic reliability of electrolytic capacitors. They are probably still being made to high standards but they are now subject to higher stresses. 

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