[R-390] Tech Query R-390 power supply

[Roy Morgan]

At 09:39 AM 3/29/2007, "Harold Hairston" <k4hca at alltel.net> wrote:
>Hi, Roy;
>
>Thanks for this helpful inforation. However, I have The A version of the 
>R-390. Are there similiar concerns in the "A" model?

Harold,

I thought that the A model also has these 47 oohm resistors in the 
rectifier cathodes, but the schematic in the Y2K manual does not show 
them.  There is a single series resistor feeding the input choke, however 
with the note: "200-220 ohms See EIB 895".  I can't find reference to that 
EIB with the Adobe Reader search in the Y2K Release 2  manual other than 
references to it in drawings.

Very likely this resistor is added as part of, or after, the solid state 
mod for the rectifiers (That field change was done with a different EIB 
number.).  This resistor is in the Audio Deck, and goes between P-119 pin 5 
(the DC input from the power supply via the B+ fuse) and the input to choke 
L602.  It is likely a 5 watt power resistor mounted with a bolt to the chassis.

If what I assume is right, then it would be quite possible to have an audio 
deck withOUT the series resistor, and a power supply WITH the solid state 
rectifiers.  This would be bad.

>  I have mine out of the cabinet to repair The Zero Adjust feature and 
> will check these items if need be.

I would get the audio module out and see if that series resistor is in 
there. If it's a field change, I would add it to increase life of the 
rectifier tubes. If your power supply uses the diodes, then it might be 
optional depending on how rugged your diodes are.

Roy


- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing
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