[MRCA] 6AK5/5654

[KA1LHZ]

I'll look in the 'Shed from Hell' to see if I have any that need to be
re-homed.
Steve
KA1LHZ

On 02/28/2014 02:27 PM, 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 project 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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