tubes age 32
bought spares for an emergency found this out the hard way. It is best to rotate
them on a yearly basis.
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Date: Tue, 25 Jan 2000 12:21:07 -0700
Subject: Re: [R-390] Spurious Intermittent Help...
Hi well it seems that the problems were tube related... I have tested and
swapped out ALL of the tubes in the rig... the 6AK5 Crystal Osc., and also one
of the 5749/6BA6W IF tubes were both in very poor condition... the OA2 was
replaced, and the B+ now reads 151.85 VDC.. the 2 plug in Filter Caps were
also replaced with 2 other sets that are known to be good, and this made a
slight improvement also... the Spur seems to have been related to the very
weak 6AK5 tube, and the intermittent loss of gain seems to have been tied to
the 6BA6 tube..I now have audio that is much cleaner and the spurs are no
longer present... There is still a very slight amount of audio distortion , but it is
only apparent with the RF gain backed off to between 5-6....I still have to try to
check the small caps in the VFO which still causes the PTO to jump after an
hour or so, but the remaining work cleaning and lubricating the PTO has greatly
improved the drifting that was noticed... The rig will hold Zero Beat to within 1
cps for hours, after the jump has occurred... as a test I left the rig on for 48
hours, and it is very stable, again AFTER the PTO jump...Thanks to All who
forwarded ideas and tips on the problem... Once I get it back in the cabinet, I
will compare the Audio and Stability with my 67 EAC... One thing I have noticed ,
is that the EAC 390A has much more audio output at lower levels than the S-W ,
when the audio gain is at 0 on the EAC, it is still clearly audible whereas on the
S-W it is audible but at a MUCH lower level... I will swap the Audio deck out with
another one once the PTO work is complete....
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Date: Tue, 25 Jan 2000 23:15:07 -0600
Subject: Re: [R-390] fixin' gassy tubes
I used to notice that the getter material in some small tubes was in the form of
a ring that probably was heated by coupling to an RF coil.
And the process was stopped automatically when the ring burned open. Likely
only Nolan's lighter or candle will heat the getter material now.
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Date: Wed, 02 Feb 2000 20:07:59 -0600
Subject: Re: [R-390] R390/A Prices and blue 6AK6's
>I went tube shopping today to locate some 6AK6's to replace my pretty blue
glow ones.
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