[R-390] maintenance

[Flowertime01 at wmconnect.com]

Very odd.  So odd, I'd be more inclined to think you have two 
erroneous tube testers.  The 390 beats on some of its tubes, but the 
RF and IF tubes (for example) should run 24/7 for a large part of a 
century without any sign of low emission or transconductance, even 
with poor ventilation.

Best regards,

Don 
--------------------------------

Don,

I think this one needs to go over to Myth Busters.

I will give you an easy 20 years. but a 100 years is pushing it.
The military wanted us to test tubes every month.
We drew the line at six months as just shoving the tubes into the TV7
socket savers was wearing the socket savers out. And we did not have any 
skate time when doing the tubes six times as often.

The way these receivers use some of its tubes has given us all a false sense 
of how long tubes should last. Tubes get out there with that pink bunny and we 
are amazed when a tube in a receiver gives it up.

Never give up a tube on time in use.
Run it until it opens the filament, glows blue, or test bad on the tube 
tester.
Then try to rejuvenate it and get some more use out of it.

But every 5000 operating hours do push the tube through a tube tester.
The whole premise of Preventive Maintenance (PM) is that its easier to 
correct a problem before it goes to total smoke than fix the problem after smoke.

---------------------------
Didn't Nolan Lee keep his on 24/7 and only took one down when it had  
a problem?  Seems I remember some of his were online for years, only  
taken down for periodic mechanical maintenance/lubrication.

Tom NU4G
------------------------------------------
The military keep thousands of these receiver up 24/7 and only took them down 
for less than 4 hours once every six months for periodic maintenance. In the 
short four hours every tube went through a tube tester, The front panel got 
washed, the mechanical alignment was checked, the RF deck aligned (peaked) and 
the signal to noise checked at each of the RF deck alignment frequencies. Check 
for a cal tone on every MHz. Checked the VFO end point span.

You humped it for about 4 hours and put the receiver back in the rack. Other 
than a selenium bridge we never had any thing smoke. Loose clamps, a broken 
core spring, a broken gear clamp was the extent of problems. 

In thousands of receivers over years, a few bad filters, that electrolytic 
cap in the audio deck leaking, dial counters falling apart, broken clamps. Bad 
spline bolts on clamps, bridge rectifier, 47 ohm resistor in R390 because a 
6082 went. There were one of these or those other thing type problems in a year. 

But thousands of receivers went forever with just Simi tube testing and the 
PM procedure in the TM. RF alignment did improve signal to noise and sensitive.

IF deck alignment was limited to peaking the IF filter caps. We never checked 
the slugs in the IF deck cans as they were always still at peak and you got 
nothing for the effort. 

We checked tubes every six months and culled the bad ones.

There is a world of difference in Lee saying he keep his receivers up for 
years with regular PM and saying he keep his receivers up for years and never 
touched any thing more than the knobs.

---------------------
I read a lot of funny things on this list, this is one of the better ones, 22 
bad (really bad) tubes but the radio still works good, did I miss something??

Joe W2DBO
---------------------------
Joe,

Not at all, 22 bad tubes is the span between a good receiver and a wonderful 
receiver. 

Charles A Taylor    Reported he has 20 plus years on a pair of 26Z5's 

Just age does not hurt tubes. Run them until they fail the tube tester.

Do not be amazed when random chance gives you a larger number of failed
tubes in one PM. 

Even a good R390 will put any signal on the antenna into your ear. A 
wonderful R390 just includes less noise in the process. If your antenna is setting in 
a high noise field you are unable to determine that the R390 is adding noise, 
as the noise it is adding may still be in below the noise level of your 
environment. If our ears were good calibrated instruments, we would not be hanging 
meters off the receivers when doing test, measurement and alignments.

Every R390 I listened to that was working sounded good to me. I cannot hear 
more signals with 30:1 signal to noise ratio from a receiver than from a 
receiver with a 5:1 signal to noise ratio. I just depended on the test meter to give 
me a reading. Better numbers are better receiver performance. I cannot listen 
to a receiver to check the signal to noise ratio. 

I hear a much better signal from a wonderful receiver with 30:1 signal to 
noise ratio but I do not hear any more signals than from a good receiver with a 
lower signal to noise ratio. 

Roger AI4NI

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