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dynaco FM-3

24.218.15.71
Posted on October 24, 2009 at 04:11:41
howardnair
Forum--i have a fm-3 that i have performed the van alstine suggestions on and the tuner works exceedingly well[ i live 30 miles out to sea]--for about an hour or so then it loses the sensitivity for several stations-something is obviously getting hot-- what is a good way to isolate this issue--also--the fm-3 zone and ebay sell some pec cards--i also have a sheet on how to build them-fromsheldon stokes--are any of these a better option---thanks howie nair

RE: dynaco FM-3, posted on October 24, 2009 at 08:17:55
GP49
Audiophile

Posts: 111
Location: No Cal
Joined: April 21, 2009
 If you mean the de-emphasis boards, yes...you can even solder up your own and do better than what was in the originals. But you need to solve the desensitizing problem first. I would suspect that there is a poor solder connection somewhere. There are hundreds of them, any of which could have been done poorly by the original kit builder. I would start in the RF amplifier stage, then in the IF section but you'll find as many differing opinions as you'll find technicians! It's not likely to be in the oscillator because most of the time anything there results in frequency drift.
GP49
RE: dynaco FM-3, posted on October 24, 2009 at 18:21:48
howardnair
 gp49 thanks--i actually resoldered everything and cleaned all with a soft toothbrush--on your suggestion i will go back and have a slow look--a little more info--i live off the mass coast--when the tuner is first on i get wgbh and wumb easily-- after an hour or so i cannot get these--but can pickup stronger stations-anyway i will go and fire the soldering iron up and get a magnifying glass and look at a few parts--here is a thought tell me if this is a good idea --after the unit gets hot could i take a air compressor or a can of compressed air and cool a spot to see if there is a change in reception--my concern is would the cooling cause too sudden a temp change???--howie

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