[R-390] Restoring my '390

[Flowertime01 at wmconnect.com]

Brian KA9EGW,

I think 24 x 7 x 52 x 5 is a bit long. Tubes will last almost forever but 
43,680 hours is mostly over the line. I think Rick Mish got miss quoted. Or 
lets not take that exact statement to literal.

Think about 10,000 operating hours on a good tube. For the first 720 - 
1,000 hours you hope the thing will quite down and get stable. From 1,000 to 
2,000 hours you hope it will quite down and get stable, because it did not do 
it in the first 1,000 hours. Then you get about 7,000 hours of good tube 
life. Then the tube starts to get noisy from what ever its mellow point was.

If you are going to do a PM and change some tubes. Go whole hog and get all 
the 6DC6, 6C4's, 5654's and 5759's in the IF string. Swap the in line 
5749's off to the VFO and BFO. Move out any 6AK6's and 5814's that will help get 
some noise out of the signal to noise ratio.

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 
them one at a time just do them all. Get it over with and start aging a 
whole new set of replacements.

One of the Fellows asked about doing this himself last week. Your time as a 
radio repairman is easily worth $25.00 an hour. On top of that you would 
like some return on the assets of the shop equipment and mark up on parts 
inventory. A good semi PM can easily go out 8 plus hours and never get to a wash 
and lube.

I am not into painting front panels. When I think about looking at paint, I 
prefer some other art than standard gray on metal with white trim and black 
contrasting knobs.

But if you must repaint that panel, under stand the real hours of time, 
real skill and real value added. I am making some different choices, But I 
appreciate the cost of a refinished front panel. When some Fellows ask $1,200.00 
plus for a specific receiver setting on a specific bench and want shipping 
extra, I do not even flinch. I under stand from where they are coming and I 
see the value in what they are offering.

Thinking of the value that is added, I see why so many on this reflector 
are doing their own maintenance. 

Please do share your rework experience with us. Ask what ever questions you 
need. More than one of us will offer up some ideas of how to proceed. You 
should have no trouble getting your receiver fully operational and into 
excellent alignment. 

Happy to have you with us.

Roger Ruszkowski AI4NI