[Hallicrafters] Hallicrafters Digest, Vol 67, Issue 17

[james.liles]

Hi Walt

The problem with these resistors is that they are carbon composition 
carrying RF.  They have the same skin effect properties as wire --- the flow 
is forced to the surface causing the resistor to overheat even though the 
rated heat as calculated for DC is not exceeded.  The 10 meter segment of 
the SR-150 tank is nearly always melted --- same reason.  A good choice for 
a replacement is carbon film or metal film resistor.  Or if using a carbon 
composition, watts times four at HF.     Kindest regards Jim K9AXN



Original message:

> Date: Fri, 14 Aug 2009 17:51:42 -0500
> From: "Walt Cates" <cateswa at msn.com>
> Subject: [Hallicrafters] SR-400A PA cathode resistors
> To: "hallicrafters" <hallicrafters at mailman.qth.net>
> Message-ID: <BLU143-DS4ECF169A0F86ACD9686BEB3020 at phx.gbl>
> Content-Type: text/plain; charset="iso-8859-1"
>
> On virtually all of the 400A's I have worked on the 13 ohm resistors in 
> the cathode ckts have been discolored. They measure from 19 to 25 ohms. I 
> have always replaced them and went on. My 400A which I restored only about 
> a year ago had the same "problem" when I got it. After one year and 
> probably less than 10 hours of actual TX time the power has began to drop 
> off. I opened it today and you guessed it the 13 ohm resistors are way out 
> of tolerance again. I haven't determined if this is the cause of the power 
> drop off yet. But, I thought I would quarry the group to see if there have 
> been any changes or improvements that I haven't heard of.
>
> Best Regards, Walt Cates, WD0GOF, 
> http://www.myhamshack.com/WD0GOF/<http://www.myhamshack.com/WD0GOF/>
>