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Astor HQ with Dual Piston variable Capacitor
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Return to top of page · Post #: 16 · Written at 10:10:28 AM on 7 June 2018.
	Marcc Location: Wangaratta, VIC Member since 21 February 2009 Member #: 438 Postcount: 5257
Causes of instability can manifest from several causes. Tube shielding is one, but with the exception of a few, is less of a problem with miniature types: Voltage is another. Bad resistors & situations exacerbated by leaking coupling caps also. I have not seen any wax paper caps recently that do not leak and most leak outside of limits. To me any non polarised cap the leaks is a dud. Tampering is also the first thing to look for, that is where I find most mistakes, & wrong parts before I even bother to fire it up. Often I will not fire up a radio before inflicting repairs. There are faults like resistors going open that will cause a slow fail. The most unstable area is the detector first audio. Lead dress is important, as induction and radiation in that area can be a major issue. Using modern caps which have no "outside foil" can in themselves be the cause of instability manifesting as oscillation.

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