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 Post subject: Quick R390A question
PostPosted: Apr Sun 28, 2019 5:10 pm 
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Joined: Jul Tue 05, 2011 8:20 pm
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Location: Chicago, IL
Are these (red) caps the "deadly" caps that need to be replaced in the mechanical filter section of the 390A? Just trying to make sure I replace the right ones in order to ensure my radio never kills those filters.

Thanks
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 Post subject: Re: Quick R390A question
PostPosted: Apr Sun 28, 2019 5:38 pm 
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It's C-553, the 0.01 plate blocking capacitor for V-501. That cap shorts and the B+ then frys the wire inside which ever filter happens to be selected. Change C-553 to a 600V 0.01.

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 Post subject: Re: Quick R390A question
PostPosted: Apr Sun 28, 2019 6:17 pm 
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So just that one cap? Looks like the red ones I have pictured are mica so less likely to be an issue... C553 is under the chassis?


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 Post subject: Re: Quick R390A question
PostPosted: Apr Sun 28, 2019 7:04 pm 
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That would be it, Look at TB502, bottom side.

You might also look/review THIS as well

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 Post subject: Re: Quick R390A question
PostPosted: Apr Sun 28, 2019 11:13 pm 
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Here's an old picture from Chuck Rippel's sadly-now-defunct R-390A page showing C-553's location:
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And here's one pointing out the location of C-549, which apparently can cause audio issues if it fails:
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C549_small.jpg
C549_small.jpg [ 88.25 KiB | Viewed 492 times ]

That page and more like it can be found archived here.
-Adam

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 Post subject: Re: Quick R390A question
PostPosted: Apr Mon 29, 2019 2:04 am 
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Joined: Sep Thu 01, 2016 3:56 am
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Location: San Jose, Ca.
Gary, Welcome to the wonderful R-390A.

The link included in Mike's post to the 'Radio Boulevard Western Historic Radio Museum Rebuilding the R-390A Receivers' is an excellent article, but there are many more as pointed to by Adam. There's also the r-390a.net disk.

One very important aspect about the C553 filter killer cap - it should NOT be a 'metalized foil' type, but should be a good 'film and foil' type cap. Thank you Charles Steinmetz. The reason for the high voltage is that they are always a better quality cap. The recommended types are SBE orange drops such as 225P, 418P, and 715P (larger).

Have fun. It's worth it.

Regards, Larry


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 Post subject: Re: Quick R390A question
PostPosted: Apr Mon 29, 2019 3:03 am 
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More on the doc for the R-390A. Here's a link to Chuck Rippel's R-390A page in the Archives: https://web.archive.org/web/20090204164 ... hnical.htm . There's still a lot of good info available only here.

Here's a link to Scott Seickel's 'gear rebuild' doc, which includes good pictures: http://www.r-390a.net/R-390A-Gear-Rebuild.pdf that is mentioned in Henry Rogers' rebuild page on Radio Boulevard.

Regards, Larry


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 Post subject: Re: Quick R390A question
PostPosted: Apr Mon 29, 2019 11:57 am 
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Joined: Jul Tue 05, 2011 8:20 pm
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Location: Chicago, IL
Many thanks for all the replies. I have had this EAC 390A for many years and it is in like-new shape with a dead-on PTO. I haven't touched it now in several years so I thought it was high time to get peace of mind by doing this simple fix before I go back to using it.

It is such a great radio...


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 Post subject: Re: Quick R390A question
PostPosted: Apr Mon 29, 2019 1:16 pm 
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Lar H wrote:

Here's a link to Scott Seickel's 'gear rebuild' doc, which includes good pictures: http://www.r-390a.net/R-390A-Gear-Rebuild.pdf that is mentioned in Henry Rogers' rebuild page on Radio Boulevard.


Hey, that is me! It seems so long ago I did that. I figured it was floating around out there in the ether somewhere....


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 Post subject: Re: Quick R390A question
PostPosted: Apr Mon 29, 2019 2:45 pm 
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I haven't looked for availability, but would this be a place for a type-Y safety cap, or would failing open give problems?

Just curious. Haven't got a R390A or plans to get one, but the thought hit me that it might be a spot to use them. No need for a detailed "why not", as I said...just curious.

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 Post subject: Re: Quick R390A question
PostPosted: Apr Mon 29, 2019 6:47 pm 
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Tony Wells wrote:
I haven't looked for availability, but would this be a place for a type-Y safety cap, or would failing open give problems?

Just curious. Haven't got a R390A or plans to get one, but the thought hit me that it might be a spot to use them. No need for a detailed "why not", as I said...just curious.

I don't think that failing open would cause an issue, but I'm not sure that a Y-rated capacitor would be proper for C-553 since they're rated for AC volts, and the capacitor would only be encountering DC. I used Sprague Orange Drops (forget which type) to replace both C-553 and C-549, which were originally metal-cased "WestCaps" in my '67 EAC R-390A.
-Adam

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 Post subject: Re: Quick R390A question
PostPosted: Apr Tue 30, 2019 12:03 am 
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A quick google says AC caps can be used for DC, but not the reverse. Of course, since it's on the Internet, it MUST be true . :D

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 Post subject: Re: Quick R390A question
PostPosted: Apr Tue 30, 2019 12:31 am 
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Tony Wells wrote:
A quick google says AC caps can be used for DC, but not the reverse. Of course, since it's on the Internet, it MUST be true . :D

Of course, no truth. A DC rated capacitor is usually rated about 2.8 times higher than the AC rating, but things such as frequency and heating can change that. Best to look up the data sheet of the particular capacitor. Capacitors made to go on AC lines are usually rated in AC, where others are rated in DC. It is better to rate capacitors seeing line AC, such as line filter capacitors and motor capacitors in AC.


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