[R-390] Re-R390 Putting a Cap on Caps

[KU4YP]

to change the pace,

	i have never owned an r-390 (a) and am looking to purchase one this 
year. i found this list last year and have enjoyed reading the 
conversations from the list.

	could someone offer a newbie some pointers on hwat to look for? i don't 
mind doing resoration work but want to start with a complete receiver so 
i can see what to replace. as i become more experienced i may tackle 
something like building one from parts.

	the receiver will go with my dx-100 and other am transmitters. like 
many hams, i am also a swl and enjoy the broadcast bands.

	so, any help anyone is will to give will be appreciated. i know you can 
buy r-390a's from with sub meters for $575.00. used repairable for $325. 
checked for $520.00. has anyone purchased from fair radio? or can 
someone suggest another source.

	i know r-390's are for sale on the auction sites but from what i have 
seen, they have often been more expensive than one i can purchase from 
fair. i understand the manufacturer of the r-390 will have some bearing 
on it's price. maybe that's why most have been more expensive.

	this is surely the well of knowledge for r-390s. your attention in this 
matter is appreciated.

	73 mike prevatt
	ku4yp


J.Byers wrote:
> This subject is getting out if hand and seems to have been been aided and abetted 
> by a post making an overly simplistic statement on statistics.
> (Accurate on  paper, perhaps, but not in practice)
> 
> With some trepidation I submit these observations.
> 
> 1.    WE all know there were many manufacturers of the R390 series, apart from Collins
> 
> 2.    Its HIGHLY unlikely the caps referred to were ALL sourced from the same 
>         manufacturer so that its equally unlikely ALL R390's EVER made had caps fitted 
>         which were came  from the same production line
> 
> 3.    The quality of caps made by different factories WILL vary, even if the initial tests
>         on these caps satisfied the militray procurement criteria.... which dictated a 
>         'normal' service life of these components, and which ALL of them seemed to pass OK
> 
> 4      These fine  receivers are all well past their (military) 'use by' date .
> 
> 5..    SO ANY STATISTICS DONE MUST ALSO INCLUDE A 'Q'  FACTOR ALLOWING FOR 
>         SUCH MANUFACTURING DIFFERENCES ON  THE EXTENDED LIFE OF THE 'C's' !
>         Ie : Consistency of potting mix, property spread of dielectric material, sealing of wire ends
>         to mould and probably many other things I don't know about to boot  !
>  
> 6.    Dummer was  a respected UK scientist , specialising on component reliability, who published 
>        a great deal of information on this subject  via UK HMSO.
>        There were a few of his  articles in the old Wireless World on this and I remember reading 
>        one of his text  books which discussed such moulded types as dicussed here..
>        He mentions that a major source of failure was moisture creepage along the wire ends getting into
>        the mould cavities (Ie cavities filled by wire and the 'C' guts).   
>        The effect of corrosion caused by moisture is to pressurise the internals which can lead to cracking
>        of the casing. This leads to more moisture ingress and is comulative.
>         Improvements to wire sealing within the mould were one of his suggestions at the time.
>         (Of course there are other failure modes apart from this)
>  
>       So any 'statistics' should  show runs of receivers with failures rates higher than others based on the
>       MANUFACTURERS  FACTORY through which component sourcing may be traced.
>       (I am merely repeating what an acknowledged expert on component reliability has already said)
>       Indeed, it may be that a single R390 had MULTIPLE CAP SOURCES from different manufacturers
>       in order to keep contract production rates going !  
> 
> SO:   WALTER  was quite correct in his statement.that such caps were consistently cracking.
> 
> And the others may well be correct  in thier observation that none had cracked !
> 
> Its likely that the spread band of good and bad 'C's  may well be due to effects as noted above
>  (in addition to many other 'noise' factors as well, such as exposure and electrical overstressing, etc etc.)
> 
> NOW I am restoring my own R390.
>   I WILL RETAIN AS MANY OF THESE COMPONENTS AS I CAN  simply because I like the look
>  of them and they ARE part of the history of the receiver. !!!
> YES,  ITS A NOSTALGIA THING !!
> 
> I can afford to do that as I am capable of and will be fixing it myself
> 
> (I will replace ALL critical 'C's' as gleaned from all you experenced fellows out there, which is what Mailmans
> excellent service is all about)
> 
> BUT:  If I were given the job of restoring someone else R390,  I WOULD TEND TO REPLACE MOST, IF
> NOT ALL these parts ,,,,,,,,,,,,  depending on what my clients wishes were.
> After all, resistors and wire end capacitors are relatively inexpensive things to replace
> 
> And my reputation on doing a professional  job  of repair would depend on so doing
> 
> To check each Cap PROPERLY  you have to lift off at least one end, and to my mind once youve gone  that far 
> your half way  to replacing  the thing with a modern, much more reliably made one
> .
> But.... and there's the rub.... its not 'original'  any more, is it?
> That too may be important to both a repairer and a client.
> 
> Lets end this silly  bickering
> 
> BOTH sides  may just be  right enough in there own observations
> 
> John Byers
> 
> 
> 
> 
> 
>  
> 
> 
>  
>         
> _____________________________________________________________
> Win a new Icom IC-756PROIII and help QSL/QTH.net
> Details at: http://mailman.qth.net/index.html
> _____________________________________________________________
> R-390 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/r-390
> Help: http://mailman.qth.net/faq.htm
> Post: mailto:R-390 at mailman.qth.net
> Unsubscribe: http://mailman.qth.net/mailman/options/r-390
> 
>