[ARC5] ARC R-511 Capacitor Failure

Wed Jan 30 01:20:13 EST 2019

When I fire up (no pun intended) a WW2 rig for the first time, I do a number of pre-tests, but the hot-cap test is very important. After a few minutes of on-time, all power goes off. Then I check the caps. All warm caps get replaced. Then I do it again. My primary BC-946-B is on for many hours every week. The only time smoke came out was when I “assumed” I had the right voltage replacement cap in the wrong circuit… A fuse would not have popped with the minimal current increase, but the smoke signals and audio silence certainly got my attention. I try not to run these radios when I am not in the shack. The designs and manufacturing are amazing, but time does its toll…

Andy W5ACM

First license WN5ZIB 1969

From: arc5-bounces at mailman.qth.net [mailto:arc5-bounces at mailman.qth.net] On Behalf Of hwhall at compuserve.com
Sent: Wednesday, January 30, 2019 12:07 AM
To: n3rht at yahoo.com; kn7sfz at gmail.com; arc5 at mailman.qth.net; aaf-radio-1 at aafradio.org
Subject: Re: [ARC5] ARC R-511 Capacitor Failure

Or a current limiter circuit?  There's one made from 2 transistors+2 resistors, and a simple one made with a LM317.  Might be cool to figure out how to make them show an indication of triggering, though.

Wayne 

WB4OGM

-----Original Message-----
From: Don Merz via ARC5 <arc5 at mailman.qth.net <mailto:arc5 at mailman.qth.net> >
To: kn7sfz <kn7sfz at gmail.com <mailto:kn7sfz at gmail.com> >; arc5 <arc5 at mailman.qth.net <mailto:arc5 at mailman.qth.net> >; Michael Hanz <aaf-radio-1 at aafradio.org <mailto:aaf-radio-1 at aafradio.org> >
Sent: Tue, Jan 29, 2019 10:22 am
Subject: Re: [ARC5] ARC R-511 Capacitor Failure

What about some more modern current protection devices like PTC resettable fuses and the TVS? 

73, Don Merz, N3RHT

On Tuesday, January 29, 2019, 8:41:29 AM EST, Michael Hanz <aaf-radio-1 at aafradio.org <mailto:aaf-radio-1 at aafradio.org> > wrote: 

Fuses are notoriously inaccurate in their operation.  I use an old HP 0-40v 5A supply from a hamfest that I discovered had an unlabled overcurrent crowbar circuit added to it sometime after manufacture.  When you set it to a few milliamperes over the normal current draw of the radio, it shuts the voltage output down to zero whenever the current exceeds that set figure.  It's a bit touchy to set the crowbar control at first, but if you are going to do any testing for any length of time, it's a useful safeguard.  However, I can't emphasize enough the need to frequently check electrolytic capacitor temperatures when you're evaluating an old set, especially if for some reason you haven't been able to check electrolytic leakage currents.  A laser infrared thermometer is really useful for that function - it does reduce the burned finger syndrome. 

         73,
- Mike  KC4TOS

On 1/28/2019 4:22 PM, kn7sfz wrote:

So, if you have a radio that is otherwise running fine with the original caps, what might be a proper size fuse to put inline with the HV to protect the dynamotor and everything else downstream? (unobtrusive mod easily reversed)

de Richard kn7sfz

On 1/28/2019 1:12 PM, Kenneth G. Gordon wrote:

On 28 Jan 2019 at 20:58, J Mcvey via ARC5 wrote:

The filter cap on the HV line is the only one I've seen totally short. the others are 
usually just leaky as hell.

I had one of those triple section 0.22 mfd job short out while I was using a receiver. As you 
say, bogged the dynamotor down like mad. Lucky I was right beside it when this happened.

I had a similar event with an ARC-5 R-23 . It was running fine for about an hour 
when all of a sudden i heard the dynamotor bog down and the radio went dead I 
was right next to it, so i hit the switch quickly. Fortunately ,there was no 
explosion. After that, my SOP is open and re-stuff all of the "flower pots".
Even the leaky ones degrade the performance and cause a higher current drain, 
so it's better to replace them and be done with it.

I completely agree with you on this one. By now ALL of those things are leaking or shorted.

If one wants to have his receiver remain completely stock, then put it on a shelf and look at 
it. 

If one wants to have his receiver LOOK completely stock, yet wants to USE it, then restuff 
them. 

Otherwise replace every darned one of them with modern caps, before something 
irreplaceable burns up.

Ken W7EKB

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