[Milsurplus] BC-221-AK resistor replacement question

[WA5CAB at cs.com]

Hutch,

There are actually two issues here.  The first is resistor type.  And the 
second is value tolerance.  

The current crop of technicians have been trained to distrust (i.e., hate) 
carbon composition resistors but without the benefit of any data indicating that 
current production carbon comp resistors have the same 50 year drift rate as 
ones made 65 years ago (and without similar long period data on carbon film or 
metal film, either).  So the short answer to the first issue is that no one 
has any data yet indicating any clear benefit of one type over the other two.  
And won't for another half century.

On the second issue, the tolerance issue is immaterial.  If the original sets 
were made with 5% tolerance resistors, then either the exact value didn't 
matter or it did.  If it didn't matter then, it doesn't matter now.  If it 
mattered then, and the original value was say 3% high, then you need to replace the 
original resistor with one 3% higher than the nominal value regardless of the 
current tolerance.  Not with one with tight tolerance to the nominal value but 
that is now 3% low compared to what the calibration book was typed up to 
match.

Plus to add further complications, the various capacitance values have no 
doubt changed since the early 40's.  Hopefully, no one was dumb enough to MFP 
treat the coil and capacitor area.

In a message dated 12/4/2008 9:37:30 PM Central Standard Time, 
olegerityincj at austin.rr.com writes: 
> List Members-
> 
> Replacing the critical resistors on the Master Oscillator coils.  Do I 
> use the
> 1. Old style Carbon comp with 5% tolerance? or
> 2. the newer type carbon film 1% tolerance? or 
> 3. the newer type metal film .5% tolerance?
> Thanks
> Hutch
> 

Robert & Susan Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480
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