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Success Stories If you have successfully repaired or restored a piece of equipment, why not write up what you did and post details here. Particularly if it was interesting, unusual or challenging. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 29th Sep 2004, 5:18 pm   #1
Ghostuser
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Join Date: Oct 2003
Location: Alton, Hampshire, UK.
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Default Ekco PB189 Motor Tuned Radio

Hi All
I have just completed repair of the above and it threw up some unusual problems on the radio side. As regards the motor tuning system, nothing was wrong that could not be put right with a good clean and replacement of rubber mounting bushes. (I usually make up such bushes from bits of grommet and small diameter rubber hose).
As for the radio, the IF, oscillator/mixer and discriminator coils have adjustable dust iron cores with fixed ceramic capacitors for tuning. ALL the ceramic capacitors had failed. I concluded this from the fact that the IFs would simply not peak anywhere near the correct frequency. Replacement and realignment gave me a good IF gain and response but no signals on any waveband. No negative volts on the oscillator grid and a high oscillator anode current told me the oscillator was dead. To my surprise, the culprit was an open circuit mica capacitor in the grid coupling circuit. Replaced, the oscillator and set burst into life. The set also uses mica padder capacitors for oscillator tracking. One of these was similarly u/s. These mica caps were not hermetically sealed like the moulded mica types which seem to last forever. Neither were they wax dipped like the more common micas. They just looked like two thin sheets of fibre/resin riveted together.

This is the first time I have found ceramic caps in a pre-1939 set and the first time I have found failed mica caps. Surprisingly, several of the waxed paper caps were fine!

Cheers
Nigel
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Old 5th Nov 2004, 10:41 am   #2
mjizycky
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Default Re: Ekco PB189 Motor Tuned Radio

Congratulations on sorting this radio out!

The failure of these ceramic capacitors is well known. They were sometimes known as "peppermint sweets" and are about as useful as same in a tuned circuit. Generally any set from this era using these should be viewed with extreme suspicion, and you might save yourself a lot of trouble if they are just changed on spec.

Last edited by Paul Stenning; 27th Dec 2004 at 1:27 pm. Reason: Fix link or code for vBulletin
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