[Hallicrafters] update SX-101 resistors

[Richard Knoppow]

>FWIW,  I've tested a large number of resistors using a Boonton 250A RX meter. This instrument measures resistance and reactance up to 250 Mhz.  I found in general that film resistors do very well up to perhaps 50 mhz, maybe higher depending on the value.  Curiously, the handbook for the 250 shows comparisons of carbon composition, carbon film and wire wound resistors as an illustration.  The film resistors have the best RF characteristics.  Carbon comp resistors are useful for a few things but in general are inferior to film types.  Composition resistors are made from a slurry of an insulating material, usually a ceramic, and carbon particles.  The problems come from the contact area of the carbon changing over time. Film resistors are stable with time and can be made very temperature stable.  They also do not have a voltage coefficient of resistance, which is typical of carbon comp. Metal film resistors can be made with either positive or negative TC or even zero TC over some range. Also, the numerous contacts in a carbon comp resistor make them noisy.  This is noise in excess of the normal thermal agitation noise found in all resistors.  Metal film are the quietest. 
>     IRC made what they called "metalized" comp resistors, I never found out what they did. IRC's have a finish that looks like tree bark. It was supposed to help dissipate heat.  Ohmite and Allen-Bradley look so nearly identical that I've wondered if they were not from the same factory. They have a smooth Bakelite case without seams.  At least the Ohmite seem to be about the most stable of the bunch.  I have seen other types which have longitudinal seams in the cases, whoever made them too many seem to be bad. 
>    I had some experience in my mis-spent youth working for a company who made established reliability metal film parts and mil spec carbon parts and had a liberal education on how they were made. Of course we didn't have laser cutters then, we used diamond saws in the trimming lathes.  
>
>-----Original Message-----
>>From: Jim Wilhite <w5jo at brightok.net>
>>Sent: May 31, 2014 3:47 PM
>>To: Hallicrafters <hallicrafters at mailman.qth.net>
>>Subject: Re: [Hallicrafters] update SX-101 resistors
>>
>>
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