[Milsurplus] 6AK5/5654

[Glenn Little]

I was a ET on a submarine while in the USN.
On one patrol we had to do ops with aircraft and I was tasked with 
ensuring the IFF was functional.
Do not remember the model, possibly a UPX-17, but, it used a LOT of 6AK5s.
As the IFF was non functional when I started, I started by checking 
the tubes with our USM-118 tube tester.
ALL of the 6AK5s tested bad, most shorted.
After requesting the required 6AK5s from supply and receiving same, I 
tested these.
Most of these were shorted, fresh from supply.
It took three rounds of requisitions to get sufficient functional 
6AK5s to get the IFF functional.
I did get the IFF working, but, there were no more 6AK5s in local 
supply when I got done.

I do not know if this was an isolated storage problem, or, a typical 
problem with 6AK5s.

Just my isolated experience/

73
Glenn
WB4UIV









At 09:27 AM 2/28/2014, Ray Fantini wrote:
>I have recently been doing lots of work on the APR-4Y receiver, have 
>one that I picked up in Dayton last year and after removing all the 
>modifications and returning the receiver back to a somewhat stock 
>configuration have to say that it's a different animal then its 
>distant relative the APR-4 or older APR-1 The APR-4Y with the 
>multiband CV253/ALR head is a good ten to fifteen dB more sensitive 
>with the ability to pick up signals down to three to five microvolts 
>in comparison to the older 4 that required thirty to forty 
>microvolts with the other advantages being that the Y supports both 
>AM and FM, has a surprisingly flat and broad IF system with 
>calibrated gain control and uses modern style seven pin tubes, and 
>that where the problem is. They used 6AK5 or 5654 for all the IF 
>stages and considering that this must be one of the first modern 
>seven pin tubes produced it has a fairly good response and noise 
>figure but between the receiver and a APA-10 companion pan adapter the two
>  of them use about twenty 5654/6AK5 tubes and I have discovered 
> that about half including almost all of them that were in the 
> APA-10 are dead. The filaments are all good but the emission is way 
> down below where it should be. I have a TV-10 tube tester that I 
> tend to believe and any of the new tubes I had pulled from stock 
> have all tested good. So the question is how do I account for the 
> high failure rate of this tube? I can speculate that maybe they 
> were cooked by the previous owners who installed stupid high levels 
> of B+ in the radios and the 6AK5 being rated for only 185 volts on 
> the plate don't like being run at 250 volts but not one hundred 
> percent on that. One thing I did do is when converting the radio 
> back for AC operation that the B+ was in the design level of 185 
> Vdc that results in the plates of the tubes being in the 175 to 180 
> Vdc range but am starting to wonder if it is natural for the 
> 6AK5/5654 to also have a short life expectancy? When I started the APR-4Y proj
>  ect I had a surplus of NOS 5654 and now to the point of looking 
> for more, wonder if I will have to plan on buying a bunch?
>
>Ray F
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