[R-390] Intial Power up ofa R30A Radio

[ToddRoberts2001@aol.com]

In a message dated 1/23/2004 12:10:27 AM Eastern Standard Time, 
k1kq@motorhomesusa.com writes:
15 of the tubes were out and in plastic bags, I checked them and then
removed the other tubes in the radio and checked them, all were good. The 2
ballast tubes I was told can not be checked, (is that correct?) and will
either light if good or not if there bad.

I am mostly concerned about this caps thing taking out the filter.

Hi Roger, OK on having all the proper tubes in the R-390A plus 2 of the 
ballast tubes. You can check the ballast tubes by checking for continuity between 
pins 2 and 7. If there is continuity then the tube is good. There have been 
articles written about a certain capacitor inside the I.F. sub-chassis that can 
'take out' the mechanical filters if it goes bad. I have seen over 100 R-390A 
receivers over the years and I have never seen one where this capacitor has 
gone bad. It certainly wouldn't hurt to replace this capacitor if someone wants 
to. If you want to be extremely careful It is best to use a variac with a 
built-in AC ammeter for initial power-up. If something is shorted across the 
receiver power supply it will show up as abnormally high current while using the 
variac to bring up the voltage gradually for initial testing. That way you can 
immediately shut things down before any real damage occurs. Ordinarily the 
electrolytic metal-can power-supply filter capacitors located on the audio 
sub-chassis seldom give any trouble. If these capacitors are bad (open) you will 
either hear a very loud hum in the audio or else the metal cans will suddenly get 
hot (shorted) and short out the power supply. 73 Todd Roberts WD4NGG.


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