[Amps] Fuse holder surprise

Jim jimw7ry at gmail.com
Tue Jun 2 21:04:17 EDT 2020

How about during normal operation? What power supply?

Jim W7RY

On 6/2/2020 7:48 PM, Artek Manuals wrote:
> During the Bench testing I have an Astron R-35 more than up to the 
> brick's challenge of 10-15 amps and fairly  short power cable less 
> than 18"
> Dave
> On 6/2/2020 8:38 PM, Jim wrote:
>> What are you using for a power supply to run this amplifier?
>> Thanks
>> 73
>> Jim W7RY
>> On 6/2/2020 7:33 PM, Artek Manuals wrote:
>>> This is going to seen trivial to many of you but some times the most 
>>> puzzling problem has the most simple solution, worth sharing.
>>> The " 60W-brick" ( an old Mirage C106) on the 220 "lets chase 
>>> DX"-repeater had given up the ghost. No power on light ...hmmm 
>>> checked and the fuse on the back panel fuse holder� looks absolutely 
>>> perfect. So out of the rack and back to the home shop for a more 
>>> detailed autopsy. After 5 minutes of poking around with the VOM it 
>>> seems the fuse is actually a zombie fuse, meaning it looks OK but in 
>>> reality it is open with no sign life or the cause of death, usually 
>>> 15 Amp fuses die pretty spectactularly. Oh well pop in a new fuse 
>>> and it is off to the races. But the amp is only putting out 40-45 W 
>>> and it is supposed to be 60W? Playing for 10 more minutes and 
>>> nothing seems out of the ordinary..oh well it is 30 years old anyway 
>>> button it up and move on to the next project right? As I put the 
>>> cover back on I happen to absent mindedly tighten the fuse holder 
>>> cap and it is VERY WARM ...now wait a minute fuse holders aren't 
>>> supposed to be that warm? Further measurement shows� a little better 
>>> than .5 volt drop across the fuse holder under load. A little 
>>> loosen-tighten cycles and it is down to .25 volts . Upon closer 
>>> inspection the spring inside the fuse holder looks dark and crusty ( 
>>> like the one in your flash light after the batteries leak). So I 
>>> have some really nice fuse holders in the junk box with bright shiny 
>>> copper insides , replace the fuse holder , no more voltage drop and 
>>> the brick is at 70W out.
>>> The moral is the old fuse holder was corroded internally to the 
>>> point that it's contact resistance had gone up enough under load to 
>>> heat the fuse contact end and melt the solder inside the fuse. The 
>>> bigger take away is that if something seems a bit odd keep looking. 
>>> This one was easy but in 50 years of tinkering I had never seen a 
>>> bad fuse holder and now I wonder how many I over looked over the 
>>> years 8^)
>>> Dave
>>> NR1DX
>>> manuals at artekmanuals.com

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