R-390A Crapout...

[Ed/KB1HYS]

Was calling CQ last night, on 3880 or so. The reciever began crackling and then a soft Pop was heard through the head phones...
Glad I have the manual... the 21st Cemtury R-390A/URR Tech Reference. Time to hit chapter 5...
Still I'll be off the air for a while. not that I was ever on that much

[WA3VJB]

Don't know Chapter 5 by heart, but I hope you checked the ballast tube.
Those iron filament things will actually make thermal noise near the end, and when they go out, you still get a little audio hiss but the PTO tube is dead (filament regulated by the ballast).  You can string a 12volt filament tube, I think something of the current like a 12AT7, across the ballast pins, and be done with it.

[The Slab Bacon]

Paul / Ed,
              Easiest fix if you've crapped out a ballast tube is to jump the 2 ballast pins with a piece of stiff wire on the top of the tube socket and swap the pto and bfo tubes from 6BA6s to 12BA6s. Nice easy mod that lasts forever and can be easily reversed if desired. 12BA6s are cheeeeaaaappp and plentiful and a pair of them, even if you have to buy them is still about 1/10 the cost of the ballast tube.
     
                                                                                                The Slab Bacon

[Ed/KB1HYS]

I'll check that out as one of the first things.  It can still hear the local comercial station but not much else. This is my first trip into the guts of the R390 so I do find it a little intimidating ... 

[WA3VJB]

Ed, your ballast may be alright if you still hear the local BC.
You say R390A in your first post, but then R390 in the second.
Very different beasts, do not abbreviate as a nickname.

Maybe a stage tube has gone out. The 6DC6 in there seem to go soft, but gradually. So does the 6AK6, and there's only one of that type in there.

If tubes all check good, try swapping like tubes into different sockets. This may reveal something the tube checker does not. Also sounds like you might want to check the internal TR relay for dirty contacts, and don't forget the fuse that protects against a destructive RF input to the receiver.  (or is that only on my R390, I forget)

A quick RF check is to use the threaded C chassis connector rather than the twinax to see if it restores signal.

As for the ballast, you wouldn't hear anything except hiss from the audio stages if the PTO fils were dark.

Frank that's good on switching to 12V BA's, why didn't I think of that.
Ed, if you get stuck, Chuck WA4HHG is an old friend of mine and perhaps can talk you through some areas to explore:

http://www.r390a.com/html/technical.htm

[Ed/KB1HYS]

Thanks Guys,

It is a R-390A. I bought if from Fair Radio some time ago. has the "after market" meters.

I fired it up tonight to find it is mearly gone hard of hearing..

I use the C connector for the antenna anyway, I will switch to the twinax side to check too. 

Thanks again for all the suggestions.

[flintstone mop]

Ed
You mean the meters that won't make you sterile  ...............hi
What a crock! We wrorry so much about radiation, let's check the black smoke coming out of those diesel trucks and busses. (Now this thread will probably self-destruct)
Do you have an RF sig gen? Hopefully it's a tube, but it sounds like a filter cap blew (you said you heard a big pop) and your B+ is very low, if you're hearing a BC station.
Fred

[W3SLK]

Ed, you maybe on to something checking the other antenna input. That aerial relay has been known to hang up. Also, I lost a 6C4 which would let you hear everything FB above 9.0 Mhz, while leaving everything below deaf.