[Milsurplus] 6AK5/5654

[Bill Riches]

Hi Ray,

I have a hundred or so 6ak5/5654 tubes.  Let me know how many you need and I
will work out a price.

73,

Bill, WA2DVU
Cape May

-----Original Message-----
From: milsurplus-bounces at mailman.qth.net
[mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of Ray Fantini
Sent: Friday, February 28, 2014 9:27 AM
To: Military Radio Collectors Association (mrca at mailman.qth.net); Military
Surplus Mail List (milsurplus at mailman.qth.net)
Subject: [Milsurplus] 6AK5/5654

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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