tubes age 222
Save the old tubes. If you have a couple that go noisy early, you swap and old
less noisy tube back in and put off doing a full refresh. If you are mixing your
best used stash into a receiver for best signal to noise with what you have on
hand, then a one pass alignment will get it. The used tubes have been burned
in. By the time you get to the alignment part, the receiver has warmed up and
likely stable.
After installing new tubes, do an electrical alignment twice. Leave the receive
on for a week and repeat the alignment if you can.
720 hours (24 x 30 days) after you do some tube changes, do another electrical
alignment. The tubes will burn in and change. An alignment will bring
improvements. At month 2 (another 720 hours) do it again. Then you should be
good for out to about 9,000 operating hours.
Once you start doing tubes one at a time you need to do that alignment with
the tube change, and again after it ages a month or so. So if you start swapping
tubes one by one as they die, you are for every doing alignment or just listening
to a less than optimum receiver.
In the past years, several of the Fellows who have been there done that, have
compared tube life and power off on cycles until the filaments break. The ratio
is to leave the receiver on for at least 2 hours when you turn it on. If you turn the
receiver on for 2 hours and then turn it off, the filaments will break just about the
time you reach the end of the tubes useful life.
Back when (68 - 75) we did a PM on a receiver each month. It got a minimum
eyeball for blue tubes and we ask the operator if it was missing any thing (like a
megahertz of signals). Twice a year (semi) the receiver went to the shop for
about 4 hours of face wash, dusting, tube checking, mechanical inspection and
electrical alignment. We used a signal generator, AC volt meter across 600
ohms (power meter) on the Local Audio output and a DC volt meter across the
diode load. On a good day we may have counted the VFO and BFO with a
counter.
Good 20:1 signal to noise from tubes was a solid year. 24 x 256 = 8760 hours.
Tubes would go another year. If you were happy with 10:1 signal to noise you
can have 20,000 hours and more. Tubes will go almost forever. If the goal is
grid voltage varies plate current and things do not smoke.
But if you are trying to eak the weak one out of the noise, do try to keep tube life
under 10,000 hours. Always your mileage will vary. Turn the receiver off when
not in use. Let it warm up a 10-20 minutes before you get into a contest.
The R390/A's are mostly over 50 years old. Any thing that is going to age and
burn in has done so. BBOD's are a problem. But again, rather than poke at
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