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Powering up an R-390A

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Powering up an R-390A Empty Powering up an R-390A

Post by LarryC on Sun Mar 16, 2008 1:15 am

I just picked up a dirty but very original condition Stewart Warner made R-390A last weekend.
The only real thing unoriginal was the 2khz filter which had been replaced at one time. Thanks to a very nice ARF member I have recived and installed a more correct filter into the IF deck. I changed out the filter killer capacitor as well. I then checked the power supply filter caps. Good thing I did, and didn't just try to power it up. affraid I found that while the caps weren't shorted, they also weren't formed anymore. So I spent some time applying voltage to them through a resistor to reform them at 300 vdc their max rated voltage.
I remove the ballast tube first in the IF section in case there was much of a power surge , hooked up a speaker and antenna and turned it on to standby. The panel lights came on and the tubes lit up ok. I then put the ballast back in and it glowed just for a few seconds as the remaining tubes lit up. I then went to full power and worked the controls and band switches a bit and started hearing signals coming through. I initially had hooked the speakers to the line output connections, bad move that seems to be for very low level audio use. When I hooked the speaker to the local output, BIG difference in volume heard. Very Happy For a set made in 1960 running on better than 98% original parts thats not too bad. I don't think this radio saw much service either. Look at it here:
http://home.earthlink.net/~chestnutl/R390A-1.html
It will need to be recapped at some point I'm sure to get best performance out of it, but I'll just clean it up a bit more, do a decent alignment and see how it sounds.
LarryC
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Post by RCWade on Mon Mar 17, 2008 12:28 pm

Just treat it gently, it's by far the best tube type radio ever designed but it can be a mechanical monster of the gears and slug tuners are out of adjustment.

RCW

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Post by Tim Tress on Sat Feb 07, 2009 12:05 pm

Don't forget that the "stock" R-390A has a 600 ohm output impedance for both the line and local audio outputs; you will need a matching transformer to use a low-impedance speaker or headphones.

There is a lot of information out there on that receiver. I would not put off the recapping job; there is one capacitor in the IF strip which will damage the mechanical filters, if it leaks and puts DC on them.

Tim KA3JRT

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Post by sprman on Sun Feb 08, 2009 2:10 pm

The line level meter is same as on my R-391 which has never been changed,all original serial #29.Believe it to be radioactive!Many that thing got dirty.Use it and be careful if you recap it.My 391 is Collins made,i use a 12 inch speaker on it with matching network.Its a good radio,but very very heavy!Sprman : )

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Post by Ken g on Sun Feb 08, 2009 2:27 pm

there is one capacitor in the IF strip which will damage the mechanical filters, if it leaks and puts DC on them.

Could someone explain where this capacitor is exactly ? I have a 390 also that looks almost brand new . I have played it a bit and it works just fine but never replaced any caps .

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Post by Tim Tress on Sun Feb 08, 2009 4:05 pm

The capacitor in question is C553, the .01 mfd. blocking capacitor on the plate of V501. It couples the signal from the plate to the filter-selector switch.

There are other known capacitor problems with the R390A; for a complete list, and much more information, see http://www.r390a.com/html/technical.htm

Schematic is here:
http://www.jvgavila.com/r390a_1.htm

Tim KA3JRT

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