[Milsurplus] 6AK5/5654

[Bill Cromwell]

Hi Glenn,

I have 22 of those tubes here all of which have passed the emissions, 
shorts, and leakage tests on my tube machine. I do not recall finding 
any bad ones over the years although I have certainly found bad tubes. 
Maybe the long arm of Murphy's Law tapped your shoulder. How much 
current did that IFF gear push through those tubes? For some 
applications attaining some critical function may be important and tube 
longevity much less so.

Artillery shells in use do not last very long at all but they do meet 
the functional needs.

73,

Bill  KU8H

On 02/28/2014 11:51 PM, Glenn Little wrote:
> 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
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> 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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