[R-390] Urban Legend Cap

[Cecil]

Sent from my iPad

On Apr 28, 2013, at 11:16 PM, L L bahr  <pulsarxp at embarqmail.com> wrote:

> Hey Wes,  Haven't the boyz told you yet ceramic discs will give you microphonics! That will be the next misinformation given.  Haven't you heard, ceramics won't give you good tone either.  Another good topic will be what type getters your tubes have in them or should you have black or gray plates in the valves!  The way I look at it, if they are good enough for my beloved Hallicrafters S-38, they will be good enough for my R-390s.  
> 
I'm not sure what boyz you speak of Lee.  Some of what you mention above is certainly relevant to vintage guitar amps and in that application is not totally hype...musicians will clear that up for you quickly.  They don't apply the technology in the same way we do in tube radios.  Can't remember the last time someone asked for smoother overdriven breakup in the push pull output stage of their SX-28A.  I think you coined it..." know of what you speak".

I would recap an S-38 from my junk box (if I had one..can't imagine that though)...something I would never do with one of my SP-600s or R-390s.

Wes as far as the work you have done on your SP-600, don't sweat it.  If its working well just enjoy using it...if you have a cap failure in the future replace it with a ceramic disk and enjoy it some more...those are easy to get to for the most part.  I do SP-600s with all ceramic disks (1kv)...it was good enough for Hammarlund and the government, works for me.  Anything you put in is better quality than the black beauties of death you took out.

I'm fixing to start work on a Racal RA-17L and will replace all the Hunts paper caps with either ceramic disks or ODs.  Won't have to revisit that work in my Sons lifetime....but that's a personal preference...certainly not the only way it could be done properly.

Cecil
K5DL

> 
> ----- Original Message -----
> I am a little confused after reading all these posts.  Can someone clarify for me:
> 1.  The self-healing film capacitors only heal with HV transits?
> 2.  How many HV transits do bypass capacitors see in a radio over time?
> 3.  Do self-healing film capacitors have a shorter MTBF than other tyoes?
> 4.  Is it wise to (or not) to use a High Voltage rated film capacitor in lower voltage circuits (like 1 KV rated in 250 VDC circuit)....basically
>      will it have longer MTBF from less voltage?
> I just re-capped my SP600 using ceramic discs in the RF deck, but metal film bypass capacitors in the rest of the radio.  Do I need to swap
> out the metal film caps with ceramic discs (or metal foil, or???)?
> Thanks for your comments.
> Wes
> 
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