National NCX-3 and NCX-A

[stuart_morgan_64]

I have acquired the above power supply and transceiver. I wish to use it myself after I have carried out necessary work. This is not a hurry job and will be a bit ongoing.

I am just looking at the PSU at the moment, seems a few mods have been done to this. I shall replace the capacitors and resistors. My question is what is the power rating of R5 and R6, why is it two resistors in series and not double the value.

Also R1 and R2, why not 15K at 20W.

Any comments will be useful. Thanks

[ms660]

R5 & R6 are 10 watts a piece according to the notes in the Schematic-Notes PDF download here:

http://bama.edebris.com/manuals/national/ncx3/

EDIT: Scroll down to the last page of that download.

Lawrence.

[G6Tanuki]

For the R1/2/3/4 network you need to consider the voltage they will see: Production- and value-engineering: manufacturers like to standardise on parts - 250-Volt-rated resistors are easy; ones rated higher get both more expensive and more-difficult-to-source.
Bought from a major supplier in significant numbers, two 250V-rated resistors in series may well work out significantly cheaper than a single 500-Volt-rated one.

Same goes for the two 330Ohm ones in series - probably cheaper to use two separate standard-range resistors (which are almost certainly also being used elsewhere in the radio as well) than need to source and stock a 660-Ohm resistor just for that one location.

[stuart_morgan_64]

That all makes sense, thank you. Still not started will be away for two weeks, and not a priority job. Thanks for the comments