[R-390] Observation on the Cap Questions and Comments

[rbethman]

I have to say that I never did any research into capacitors.

The ONLY radios I've worked on has been tube radios.  I do own two that 
aren't, but haven't had any part mortality other than a thermal switch 
in a power supply.  That particular repair I resolved by jumpering the 
failed thermal switch/sensor, and replaced the bushing 12VDC fan with a 
ball bearing computer CPU fan.  It draws less than half of what had been 
in there as manufactured.  Therefore MUCH less stress on the power 
regulator board.

The tube types have had the same style of component that was there 
replaced with a like and equally rated or sometimes with a higher 
voltage rating, and in some resistors, I've upped the wattage of the 
replacement.

I've never gone out of my way to select foil/film over metalized/film.

I've never had a failure in any instance of my replacements.

This even applies to those radios that I have helped an aspiring Amateur 
Operator when they purchased a piece of equipment that I helped them get 
on the air.

No squawks from them either.

Old oil filled caps that developed leaks were replaced with non-oil filled.

Perhaps I've been lucky?  Or is it that this has been blown way out of 
proportion?

Don't know.  The 2 BC-610s haven't complained, nor the Heathkits, nor 
the Hallicrafters that the BBODs that have had them replaced.

Bob - N0DGN

On 5/2/2013 6:30 PM, chuck.rippel at cox.net wrote:
> Some years ago, I did a good bit of research on the question while I 
> was rebuilding my 75A-4 and the first SP-600. The take-away IRT tube 
> radios was GENERALLY as follows:
>
>
> Electrolytic's are generally used as filters in power supplies; you 
> may see the odd application as a cathode bypass in an audio circuit.  
> The voltage rating of the replacement cap should be such that the 
> applied voltage, be it P-P or DC should not exceed 80% of the rated 
> voltage of the cap.
>
> In circuits in which audio or RF up to but not exceeding 455KC in 
> frequency, Sprague Orangedrops work wonderfully and Orangedrops with 
> Polypropylene media (the more modern 716P Series) in particular, 
> excell in audio circuits.
>
> Circuits which have RF whose frequency exceeds 455KC in benefit from 
> Ceramic Discs.  1KV rated caps, in my book, are considered a minimum.
>
>
> As an example, the average SP-600JXxx will need something on the order 
> of 38 .01 ceramics, 16 .022 Orangedrops a couple .5's and one Multi 
> Section Electrolytic filter cap.
>
> I use 600V, 715P Orangedrops to replace the dreaded C-553.  I've not 
> had one fail (that I know of) in 30 years.  Because of space 
> considerations I have started using polypropylene media, 630V tubular 
> metal film caps (http://www.tubesandmore.com/products/C-U-630V) in 
> R390A audio deck boards.  The .01 audio input coupling cap, buried in 
> that same module will get a .01 Orangedrop or maybe even a .022 if I 
> can squeeze it in. Of course, there is that 8ufd electrolytic which 
> always seems to be leaking acid.  A easy to find, 10ufd, 35V axial 
> works just fine there with the (+) lead soldered to the inboard solder 
> pad.
>
> That application will yield about the best >audio detail< and overall 
> sound the radio is capable of giving.  In this case, the best possible 
> audio detail is the goal.
>
>
> ---
> No  trees were killed to deliver this message.  However, a large 
> number of electrons were terribly inconvenienced.
>
> Chuck Rippel