[R-390] Out from the shadows ...

[Joe Foley]

Nice catch!

I see you've been very busy with it.

First thing is to fix the filter caps, temporary is
good, rip the bottoms from two OLD, no good, octal
based tubes or get the bases from two "ice cube"
relays.  Clean them out and solder in some new
electrolytic caps of the proper value, this will get
the radio back up and running until you figure out
what you want to do with the old filter caps.  This
might solve the humming problem, too.  If not we'll do
something different.

Next, replace the capacitor that protects the
mechanical filters from B+, I think its C553 in the
schematics. Use and Orange Drop or similar.

While you're waiting for more information do the
resistance and voltage checks in the manual, this will
give you a baseline reference for THIS particular
radio when you need to do troubleshooting in the
future,... or, you may find something amiss now.

Any cleaning or visual inspection you do now will get
you more familiar with the radio, and lead to even
MORE questions.  Be careful with the pins on the
plugs, they are soft brass and bend/break easily. 
Tighten all ground connections while you're in there,
even the tube socket bolts, trust me, they're loose,
look for corrosion.

Look into getting a VTVM and a URM-25D signal
generator as shown in the manual.  Oh, sure, there are
better ones but the URM-25D is cheap and its the one
used in the manual,... besides, its just as
interesting as the radio!


> 
> After careful visual inspection of radio combined w/
> impression radio was taken care of, I double checked
> fuses and decided to fire it up. I was relieved when
> I
> heard the sounds of the airwaves bursting forth into
> my room. One of the first things I noticed was a
> fairly obvious hum and vibration from the power
> transformer (? largest transformer underneath) I
> pulled both rectifier tubes and radios output tubes
> but this problem persisted. Before I shut it down I
> took it up and down the bands; radio seemed
> sensative
> everywhere. All functions seemed to be working too.
> After shutting rig down I pulled both electrolytics
> ... they both have seepage.
> 
> I've since received the Field and Depot Maintenance
> Manual which is fascinating but mostly over my head.
> I've browsed the Y2K manual (but haven't downloaded
> yet), read every post to the 390 net in the archives
> (probably twice:), and spent many many hours
> checking
> out what's available on the net.  I've also been
> comparing what I've been learning, with the rig
> itself
> on the bench... it's been a blast and is really
> starting to make sense.
> 
> Since I'm mostly sure there's nothing tremendously
> wrong w/ radio my plan of action is to do the
> absolute
> minimum to the rig that'll get it up and running and
> safely. This includes (here's where I'd really
> appreciate opinions) visual inspection underneath
> modules, replacing electrolytics, and replacing two
> nasties in IF module. I'll also be putting a three
> prong power cord on radio and lubricating gear
> train. 
> 
> If it isn't obvious enough to y'all I'm very new to
> this stuff, the only similar project I've tackled
> has
> been to completely recap an HRO-60 (mission very
> much
> accomplished... I love that National) The only test
> gear I own is a multimeter. I'd love some advice re-
> hum from transformer. If after I finish my small
> list
> of "do's" and hum is still present what's next?
> 
> Oh yeah ... I'm awaiting a recap kit and bristol
> wrench kit ...
> 
> Please pardon such a long post. I wanted to say
> hello
> and let everyone know where I was at and that
> another
> of these fine radios had found it's way into some
> caring hands.
> 
> Best regards,
> Mike
> 
> 
> 		
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