[Milsurplus] [MRCA] APR-4Y project

[John Vendely]

Hi Ray,

The 6AK5 is not noted for reliability problems or short life span.  
However, I have seen quite a lot of surplus equipment over the years 
completely full of really weak tubes.  I get the impression that a lot 
of toob gear which was known to be nearing the end of its service life 
was just run until it was barely serviceable, or crapped out 
altogether.  At this point it was removed from service and declared 
surplus.  By that point, the equipment was loaded with very weak tubes.  
I've seen this on numerous occasions...

73,

John K9WT

On 2/28/2014 4:55 PM, Ray Fantini wrote:
> Only had this receiver running a couple days now and the tubes that are in there are all tested good, just surprised by the high number of 6AK5 tubes that were found bad in both the receiver and the APA display. Check all the tubes before starting work was a rule that was beat into me at a young age. Maybe the question is if the 6AK5/5654 is just a piss week tube to begin with and when driven near maximum values they wear out fast? Look at the tube charts, max plate voltage is 185 VDC and typical plate voltage is the same? Suspect whoever did the initial conversion of the receiver did not do the little tubes a favor by running 250 VDC as B+ so now that its back to 185 will see how they hold up. The disturbing thing is that it's not just the 6AK5 tubes that were in the receiver but three of the four that I pulled from the APA-10 display were also bad. Will be pulling the rest this weekend and testing them.
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> Ray F
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