[Milsurplus] RAK/RAL recap

[Bill Cromwell]

Hi Ken,

The caps are oil-filled paper caps and the leakage is electrical 
leakage. They are passing some dc current and that is a no-no. For a 
bypass cap the load on the power supply is increased and tube electrode 
voltages may be upset. Interstage coupling caps that leak will apply 
some of the plate voltage from the preceding tube at the grid of the 
next stage. Some of the bypass caps are showing as 'dead shorts' but the 
power supply did not seem to be unduly strained. I suppose at some point 
that light comes on steady but the leakage current is less than a dead 
short. The silver mica caps are also showing leakage. All of those caps 
are around about 70 years old. I am getting close to 70 years old and 
I'm feeling a little tired, too <evil grin>. I am not finding any fluid 
leakage (in the caps or otherwise). The caps can be left bolted in place 
where they might be too difficult to remove and the wires disconnected. 
I can see exactly where I am going to place the first cap - when it 
arrives - and leave the original in place.

I'm glad I have that C-2 because there is no way I could check those 
caps for electrical leakage with a voltmeter while they are in the 
receiver and with power applied from the power supply.

I had the bottom internal shield cover off - 26 screws! There is no dust 
at all inside my RAK!

73,

Bill  KU8H




On 10/06/2015 10:22 PM, Kenneth G. Gordon wrote:
> On 6 Oct 2015 at 21:39, Bill Cromwell wrote:
>
>> Hi,
>>
>> I have begun the recap of my RAK-7. Among other things I have noticed
>> that I didn't order enough caps! I overlooked some others and didn't
>> order any of some of them. When we buy a kit we usually get around those
>> issues. But I have the patience to keep after it until I get the needed
>> parts. My Heathkit C-2 cannot find *any* good caps (leakage) beyond the
>> air variables.
> Bill: I am finding this to be very interesting! Do you have any idea of the
> failure mechanism for those caps? As I remember, all of those caps are
> oil-filled types with ceramic terminals, and I am very surprised they have
> gone bad on you...or are these leaky ones a different type?
>
> I DO know that the interstage coupling caps are not those oil-filled jobs, and
> those routinely go bad.
>
> Ken W7EKB
>