[NJARC] Philco 37-650 RF Question

[Scott Roberts]

My problem with the resistor wasn't the age- I
replaced all of them- it was the wrong band... It was
supposed to be a 330k ohm, which has an
orange-orange-yellow band arrangement. What got put in
place was orange-orange-grey, or 3,3 and 8 0's- or
3,300,000,000ohm! 3,300M ohm! Which was a little high
resistance...

I can confirm what you say about age, however: I have
a box of NOS resistors from the 1950's/1960's, and
while many are still very near correct, and within
tolerance, many more are out of spec to a great
degree. These usually donate their leads to little
projects... These are all carbon comp resistors. 

Now, another resistor question. I replaced one of the
power resistors, a wirewound 9k ohm/2watt(#61) with a
combination: a 4.3k/2watt and a 4.7k/2watt, both metal
oxide. I also replaced a neighboring(#60) 10k ohm, 2
watt with a 10k/2watt metal oxide. I replaced #60
again with a 10k/5watt wirewound power resistor, but
not #61, as I could not find a 9k ohm. Would a 10k ohm
wirewound power resistor be a better one to put in
place, and could this have anyting to do with my
problem?

Thanks
Scott

--- Mbeeferman at cs.com wrote:

> Visit our web site - See http://www.njarc.org
> _______________________________________________
> Having done a little research in this area, I tend
> to agree with Jim.  A 
> rating is a rating, and functional differences
> between a 1-watt carbon composition 
> and 1-watt film resistor should not exist.  Problems
> at high frequencies come 
> into play only with wirewound substitutions.  
> I tend to believe that Bob's problem may have been
> in another area.
> The problem with carbon composition resistors,
> especially NOS, is related to 
> how critical a tolerance is required.  The process
> that creates carbon 
> composition resistors leaves them under stress. 
> Over the years, this stress is 
> eventually relieved (I won't go into the physical
> details) and the resistor can be 
> left significantly out of tolerance.  As an
> experiment, randomly select 10 NOS 
> carbons from your junk box that are greater than
> 20-30 years old and take 
> some measurements...you might be surprised.
> In any restoration project, I always`use the same
> philosophy...it might take 
> some extra time, but it is surely worth it....
> 1.  Verify what you install and don't depend on the
> markings.
> 2.  Verify what you remove (unless the component is
> completely destroyed) and 
> ensure it makes sense with regard to the circuit or
> the schematic.
> 3.  Don't make any more than 3 replacements without
> firing up the set to 
> ensure that you're not introducing more problems
> than you're trying to fix.        
> 
> _______________________________________________
> NJARC mailing list
> NJARC at mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/njarc
> 


"War is an ugly thing, but not the ugliest of things; the decayed and degraded state of moral and patriotic feelings that thinks nothing is worth war is much worse. A man who has nothing for which he is willing to fight, nothing he cares about more than his own personal safety, is a miserable creature who has no chance of being free, unless made and kept so by the exertions of better men than himself." John Stuart Mill, 'The Contest in America', Feb. 1862


__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com