[ARC5] ARC R-511 Capacitor Failure

[Michael Hanz]

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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