[R-390] C553 replacement?

[Cecil acuff]

It’s certainly one of the first that should be tested for leakage…if not just replaced because!

Cecil
K5DL

Sent from my iPad

> On Feb 26, 2023, at 8:33 PM, Dan Martin <pitfit at comcast.net> wrote:
> 
> I've read these recent C553 posts with interest and a grin.
> 
> 10-20 years ago there were stories alleged of hundreds of destroyed mechanical filters due to stock C553 failures. Puzzled operators, concerned about the mysterious loss of a filter, would quickly switch to each of the alternate filters to confirm their function and would thereby sequentially destroy the entire filter bank. Who hasn't heard those stories around a campfire?
> 
> Replacing C553 with a Sprague (now CDE) Orange Drop used to be the unquestioned first thing in any refurbishment. Chuck Rippel wouldn't let a 390A leave his shop without an Orange Drop in place for C553. 
> 
> Now it seems Vitamin Q's, like Golden Retrievers, are our best friends and never turn on us and go bad.
> 
> Really, not picking a fight, my friends. Just appreciating the comments re: what had been unquestioned convention "back in the day."
> 
> And yes, my '67 EAC has a 20 year old by-gawd Sprague Orange Drop in place for C553, not some  upstart CDE branded version. 🙂
> 
> Dan
> WB4GRA
> 
> Sent from my iPhone
> 
>> On Feb 26, 2023, at 3:16 PM, David Wise <d44617665 at hotmail.com> wrote:
>> That’s correct, C553 is a coupling cap into the R-390A mechanical filter.  It’s a catastrophe if it shorts.  Many people replace it even though it’s a Vitamin Q which should still be good.  I kept the old cap and inserted a current limiter, using a Supertex (now Microchip) LND-150 depletion-mode MOSFET.  Just connect drain upstream, and source & gate downstream, and voila, 1mA limit.
>> 
>> In the R-390, C606 sees 1/19th of 180V so it will last forever.  C608 sees about 180-10+5 or 175V.  If it leaks, the regulator will throttle down.  If you suspect this, measure voltage across 6BH6 grid resistor R624; it should be zero.  Slight leakage is worse than severe leakage, because the 6080’s will overheat.
>> 
>> On pdf page 10 of 34 of TM 11-5820-357-35P, C608 is listed as type CP10A1EE224M.  CP is hermetically-sealed paper.  In specification MIL-C-25D, the second E indicates 400 volts.
>> 
>> Dave Wise
>> SWL (Inactive)
>> 
>> Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Windows
>> 
>> From: Barry<mailto:n4buq at knology.net>
>> Sent: Saturday, February 25, 2023 8:08 PM
>> To: Jim Whartenby<mailto:old_radio at aol.com>
>> Cc: R-390 Mailing List<mailto:r-390 at mailman.qth.net>
>> Subject: Re: [R-390] C553 replacement?
>> 
>> I think C553 is only in the R390A.
>> 
>> Thanks,
>> Barry - N4BUQ
>> 
>> ----- Original Message -----
>>> From: "R-390 Mailing List" <r-390 at mailman.qth.net>
>>> To: "R-390 Mailing List" <r-390 at mailman.qth.net>
>>> Sent: Saturday, February 25, 2023 10:03:27 PM
>>> Subject: Re: [R-390] C553 replacement?
>> 
>>> A quick look at the R-390 Collins preliminary manual indicates that C-606
> 
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