[Hallicrafters] SX-73 / R-274 Starting Resto

[Richard Knoppow]

    I would just leave them alone. They may even be temperature 
compensating. Unless they are leaky (very unusual for ceramics) or have 
some other problem there is no point changing them. Mica caps are fine 
where one needs great stability. In fact polypropylene caps are even 
more stable. Drifted carbon comp resistors seem to be endemic to 
Hallicrafters rigs. All carbon comp resistors drift up and the higher 
the original value the more they drift. No matter what brand any 
resistor over about 100K should be checked and its likely those over 
about 250K will have gone quite high. My experience is that Ohmite were 
the most stable, Allen-Bradley the next best. I seldom see IRC resistors 
so I don't know about them. IRC must have either been expensive or there 
was some other problem. They advertised fairly heavily so I've always 
wondered why there are not more in commercial equipment. Anyway, 
Hallicrafters seems to have bought bargain basement resistors. So did 
National. Modern carbon film or metal film resistors are extremely 
stable, new ones will last forever.

On 1/6/2018 9:24 AM, thoyer wrote:
> Hi Richard, (and list)
> 
> Thank you for the info. I'm working the tuning section today and have found
> most of the resistors way out of tolerance.
> 
> I also did a sampling of the capacitors. They are spec'd in the BOM as being
> ceramic and look like the dog bone type. I checked a couple of the 33pf
> coupling caps and they measure over 50pf.
> 
> Now my question becomes - since they are spec'd as a ceramic dielectric
> should I replace them with ceramic or go to a mica style which is what I'm
> more accustomed to seeing in RF circuits?
> 
> Tom
> W3TA

-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL