View Single Post
  #8   Report Post  
Old September 4th 08, 09:40 PM posted to rec.radio.amateur.boatanchors
Paul P[_2_] Paul P[_2_] is offline
external usenet poster
 
First recorded activity by RadioBanter: Jun 2007
Posts: 118
Default National NC300 restoration hints needed.

Thank you all for the replies.

I printed out the BAMA schematics and the BAMA
http://bama.edebris.com/manuals/ mods for the NC300. The mods are numerous.
This chassis has none of them. This can be good or bad depending on the
collectors desires. I would think the factory mods like replacing an
unshielded wire with shielded wire would be totally collector acceptable.
The mod is fixing a design flaw identified by the factory.

I dim bulb (a kin to a variac) tested and opened up the NC300 today to start
the restoration. I was able to receive station but the dial is way off and
was unable to clarify SSB. All tubes tested good save one. The mixer is
bad. I cleaned the chassis with Clorox clean up, a tooth brush and a rag.
Now it is nice and shiny.

There is plenty of room under the chasssis for new Electrolytics. Since
this restoration will not have restuffed wax/paper caps I see no harm in the
underchassis installation. If a collectors want a "museum" level
restoration to show off the underside of the chassis then all new components
would be hidden inside origonal container, wrappers or what have you.
Reformation of the eletrolytic can is out of the question. There is dried
eletrolyte harded on the vent hole. In my not so hmble opinion - Unless I
have a published life expetancy of the capacitor or the dilectric you are
asking for a recall or burned out components when that capacitor evenually
dries up, shorts or burns up.

There are a lot of paper capacitors underside. They are dipped in some
plastic like coating. But that does not stop the deterioration of the
internal paper. Here again, I think it is best just to "shot gun" them out.

I have a habit of resistor replacement as well. This is a bit on the edge
of needs to be done or not. My lesson came from an RCA AA5. I replace all
caps and aligned. It played for a day and failed. I put it on the bench
and found the out of tolerance resistor. It measued good along with all the
rest. I repeated these steps three more times before I just decieded to
shot gun the carbon composition resistors. No more problems. If I find any
out of tolerance reisstors in this chassis I will go ahead and shot gun
these too. The chalenge is not to uses inducive carbon film resistors in
high frequency (relative to the resistor) circuits like the oscillator and
mixer section. I found that in radios that recieve less than 18 mhz all is
ok. Any thing above that then non inducive resistors must be maintianed.

More later, and thanks again to all whom contributed.

If you want to follow along I will be posting my progress on the web site at
www.ppinyot.com. It is not there yet.

Paul P.