[R-390] Urban Legend Cap

[Cecil]

Sent from my iPad

On Apr 28, 2013, at 7:53 PM, Perry Sandeen <sandeenpa at yahoo.com> wrote:

> Urban Legend Cap 
> 
> List,
> 
> Charles Steinmetz has commented extensively about problems with film foil caps.  In his usage situation these may pose a problem.
> 
> In group buys that I have made for the list over the last 9 or so years or so, I sold over 4,000 Vishay/Sprague 197LS.01 1KV 20% ceramic bypass caps for both R-390A and SP 600 radios.
> 
> On another buy I sold 1,000 .01/600 volt film bypass caps.
> 
> As the Vishay/Sprague price had risen dramatically, on the last buy I made for the group I bought 2,000 Murata DEB series .01 1KV -20 +80%.

There is no question...any and all of the above will work in the radios....I'm not sure that's ever been In question...
> 
> Let me assume for a moment that only 50% have been installed so that makes 3,500 caps.
> 
> No one has ever told me that even one has failed.

These radios are 50+ years old...the question in my mind is what kind of shape will the caps we install be in...say 30 years from now.  Many wont care because they won't be around at that point...but someone will hopefully be enjoying them...and at that point in time, point to point wired components will probably be long gone.  So an investment in decent quality parts today will prove its value in the years to come when replacement parts may not be available at all.
> 
> With that type of track record I’m not going to stuff oversized and 8 time the price (in 1,000 pieces $1.22) caps in my equipment for bypass use. 
> 
> And to add insult to injury for those who are dead-set on using them, according to the current Mouser online info, they are being discontinued.
> 
> And AFAIK all the tubular bypass caps made up until the ‘60’s were all of foil construction. Correction welcomed.

> 
> Now for a bit of logic.  IF only foil construction capacitors met current HV needs, many manufactures would be making them.  Instead just the opposite is happening.  They are all making deposited metal coated plastic types.  So besides being cheaper and smaller they are accepted as reliable by the electronics industry for high voltages.

Problem is the stuff they are building now days are designed for a useable life expectancy of about 7 years max..and much less in many cases.  I can't tell you how many flat panel TVs and computer monitors I have repaired by replacing bad electrolytic caps....things that didn't use to fail for 20 years or more in equipment designed to be durable.  That's not the quality of parts I want in my tube gear if I have a choice.
> 
> I don’t care if people choose to use OD’s for their radios.  It their preference. They can use Leyden jars if so inclined.
> 
> What I’m opposed too is this urban legend that will not die is that OD’s are necessary.  (Egor! Get the garlic, cross’s and wooden stakes!) We have new people coming to the list seeking information and are then mis-informed.   When one recaps a whole receiver, which is changing from desirable to mandatory as the sets get older, the economic difference between the two is probably around $100.  
> 
> I will wager USD $1,000.00 that no one on this list can prove that foil OD caps are measurably superior to the equivalent ceramic caps in bypass applications in BA receivers.  Any takers?

I've never seen that asserted...

I think I have seen pretty universal agreement that, in bypass applications, ceramic disks are very acceptable and more economical than using OD caps or any film/foil caps in that application.  I think it has also been pretty universally accepted that a better application for the film/foil caps would be for coupling...and if one chose to apply them in that manner, the OD would be considered the Cadillac of those type caps...but that there are other choices that one could make and and end up with a very acceptable restoration.  A good example is the Hammarlund SP-600 that was factory built with all ceramic disks for bypass and coupling...now some 60 years old and generally not in need of those caps needing replacement.

The only magic the Sprague Orange Drop has is that it is the last of the really high quality, over built film foil caps being made and as you say that may be coming to an end....and that's no Urban Legend


Cecil
K5DL
> 
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