[Heath] The DX-60B Issue - Lamp in series with the 120VAC

[Kenneth G. Gordon]

On 2 Apr 2018 at 23:09, Paul Robinson wrote:

> I do not apply full power to an old rig.  It is not necessary and can do a lot of damage. 

Yes.
 
> I like installing a 60 watt or 120 watt (120VAC) incandescent lamp in
> series with the input power.

This method is a "must" for our older gear.

>  This limits the 120VAC current to 1 or 2
> amps and prevents a lot of smoke. It also allows one to take some
> measurements.  I have been known to short the load with a clip lead
> (the DX-60 in this case) when the power is tuned on, then when the
> lamp is lit, I remove the load short.  In this way there is no surge
> to the load when the power is applied to the load.  The load sees a
> nice constant current 1 or 2 amps.   
> 
> I have also installed a switched AC outlet and an isolation
> transformer, at my bench, which I use during these times. 

These are good things to do. I do these, plus use a large Variac or a bucking transformer to 
keep the line voltage at or below 110 VAC too. My line voltage here has, at times, been 132 
VAC and "bumps" above that once in a while. This is much too high for our older gear.

> Old rigs have aluminum electrolytic capacitors which need to be slowly
> powered up (re polarized, I think is the term)

No. The word is "re-formed". Properly done, this process duplicates the manufacturer's 
ORIGINAL method of making them.

> as the leakage current
> through the capacitors will be high when power is first applied.  A
> variable transformer will allow the power to be increased slowly over
> a 10 hour or 24 hour period and this seems to work.  Again, I use a 60
> watt or 120 watt (120VAC) incandescent lamp in series with the input
> power which will limit the current if something drastic happens during
> this process.

The DC voltage applied to any electrolytic capacitor which is older than 1 year old and has 
not been used during that time should be limited so that the CURRENT into that cap will not 
exceed 5 mA. Heating of the capacitor in question should be kept to an absolute minimum in 
order to prevent damage to the electrolyte.

A Variac ahead of your DC supply MAY be used, but one must be very careful using it. It is 
often too "coarse" for  this purpose. A better choice is a large high-wattage variable resistor 
in series with the DC output lead. Properly chosen light bulbs MAY be used.

As the capacitor "reforms" that current will drop, approaching zero. The voltage applied may 
then again be raised to the 5 mA point, then left until the current drops again. This process 
should be repeated until the rated voltage level of that particular capacitor is reached, at 
which time the "leakage current" will be as low as it will ever get and the oxide layers in the 
capacitor will have been "reformed" correctly.

If the capacitor has not "reformed", i.e. if the leakage current has not reached close to zero 
mA, this process should be done again. If it STILL has not been "reformed", the capacitor 
should be thrown away as the electrolyte in it has either dried out or deteriorated.

This process duplicates the method used by the manufacturers to make the capacitor to 
begin with.

For those interested, I have a military document which details this method and the reasons 
for it. The document is a PDF and is of a size which can be sent via e-mail. Please ask for it 
off list.

Ken W7EKB

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