[R-390] Tube life/replacement?

[Bob Camp]

Hi

We had a little thread going on this a while back. More or less to 
recap:

1) There are no "weak" tubes in the 390A design other than the 
rectifiers. Since most of the radios have been converted to solid state 
rectifiers by now this is not a big issue.

2) People seem to get amazing life out of a set of tubes in stationary 
service. Reports of 10 years of use in the mode you are running were 
not uncommon.

3) The world is awash in tubes for the 390A. Finding tubes if you have 
a failure is not going to be a problem. I probably have a thousand year 
supply sitting in storage. From what I have seen that's a small supply 
compared to others on this list ....

4) I seem to recall that I was going to come up with a simple tube 
tester for those who do not already have one. Another thing I need to 
get back to some day.

If you have an extra couple hundred dollars you can grab one of the 
military tube testers at auction. They are not a perfect way to check a 
tube though.

If you have a copy of any of the manuals they have a fairly complete 
voltage listing in them. Of course that assumes you have a voltmeter 
and some tube extenders. At least they are still pretty cheap to pick 
up.

Most of the tubes used in the 390A are used multiple times. This makes 
tube swapping a reasonable approach. If you have a problem, swap a 
likely tube and see what happens. If the problem changes you have found 
a bad tube.

I can see no reason to routinely swap out tubes. Any time you change a 
RF or IF tube you need to check the alignment. Also there is no reason 
to assume a new tube will be stable until you run it a while.

	Take Care

		Bob Camp
		KB8TQ


On Dec 31, 2004, at 2:41 PM, <fraserb at quasc.com> wrote:

> Since I'm in the midst of my annual winter AM BCB Dxing season, I had 
> a thought about the life of the tubes in my R-390A.
>
> How often were tubes replaced when in service with the various govt 
> agencies?  Were different tubes replaced on certain schedules?  Were 
> tubes regulary tested or just pulled and replaced?
>
> I use my R-390A for probably somewhat less than 200 hours a year.  How 
> long are the tubes supposed to last?  How do you know when tubes are 
> less than the minimum level required?  Are there well known symptoms 
> that indicate a certain weak tube?
>
> Lost of questions to start the new year!
>
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