[R-390] Nolan - '67 EAC

[Dan Osborne]

I just turned off my '67 EAC R-390A...it's ran long enough for
now. It's going to take me a while before I can get used to
seeing a darkened dial in that rack.

All of this talk about tube life and heat shields etc. just made
me realize that it's been a week more than two years since I powered
up my '67 EAC after I put it back together.

That's 17,640 hours of 24/7 operation since October 13th of 1998.
Oops, better add a day in there, we just had a leap year. <grin>
Damn, time sure flies, huh?

In that time frame it's been setting here in the shop running
around the clock while experiencing ambient temperatures from
below freezing to well over 100 degrees.

I've had two problems with it. I slid it out of the rack after
the first thirteen months to correct what I had thought was an
AGC problem where it seemed to overload easily. This problem was
corrected by the replacement of four tubes. A 5654 (weak), a
5814A (gassy and could have been fixed) a 6DC6 (weak), and a
6C4W (weak). Other than the two rectifiers and the voltage regulator
tube, these were the original 1968 date stamped tubes that were in
the set when it was built. All of them tested OK when I checked them.
I replace the rectifiers and the regulator because of previous bad
experiences with those tube numbers.

Two months ago, it died due to an open filament in the 6DC6 while
I was sitting here listening to it. A new tube fixed it while the
body was still warm.

Right now, it works fine and exhibits zero problems. But, I suspect
that I'll end up replacing a number of tubes in it. Probably every
thing except the 3TF7. As high a mileage as they are I'd be paranoid
of them even if they tested OK. Hell, the thermal shock of powering
if back up might fry half of them with my luck. ;-(

I attribute this long life to several things. The and primary one
was the replacement of all of the paper capacitors in the receiver.
In 25 years of messing with R-390A's, this is the first one that
I've had for any length of time that didn't have a cap shorting and
taking something with it or having to spend hours and hours
troubleshooting some obscure problem that is almost always caused by
a bum cap. Come to think of it, I might have been the first person
to even consider replacing all of the paper caps in one. <grin> I
think I just dislocated my shoulder patting myself on the back. ;-)

The second is that I used heat conductive shields on all of the
tubes. The set had all of the original WPM black shields with the
inserts when I got it. I replaced the ones on the rectifiers and
the 3TF7 with extra tall NOS IERC shields and added the conductive
base inserts to some of the "critical" tube sockets. And no, In
25 years I have NEVER had a 3TF7 fail. The only replacements I've
used were for sets that had missing ones or they were bad when
I received the set.

Running it on a variac at 115 volts probably had a lot to do with
it too. My normal line voltage here is 125 volts.

On a side note, the use of the Mobil-1 synthetic motor oil for the
primary lubricant has proven to be a winner. It's easier to tune
today than it was two years ago.

I spent a hell of a lot more time checking everything when I put
it back together than I probably needed to. But all in all, it was
well worth it to me and I think that it was effort well spend.

For what it's worth, I just checked the log on one of the R-1051B's
and it's been running 24/7 since October 8, 1996. That's well over
35,000 hours. I cheat on them though and replace both of the tubes
in each one every 6 months without even bothering to check them.

nolan


Survival Kit contents check. In them you will find: one 45 caliber 
automatic, two boxes of ammunition, four days concentrated emergency 
rations, one drug issue containing antibiotics, morphine, vitamin pills, 
pep pills, sleeping pills, tranquilizer pills, one miniature combination 
Rooshan phrase book and Bible, one hundred dollars in rubles, one 
hundred dollars in gold, nine packs of chewing gum, one issue of 
prophylactics, three lipsticks, three pair of nylon stockings -- shoot, 
a fellah could have a pretty good weekend in Vegas with all that 
stuff...."   ---Dr. Strangelove---

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