[Boatanchors] SB-610 problem update/solution - Voltage rating on resistors

[Barry L. Ornitz]

Bill, K0JWP, wrote:

> I'm pleased to report that using a combination of your 
> suggestions (which included replacing the three, 1/2 watt 
> resistors in the intensity/focus pot circuits along with 
> replacing all eight electrolytic capacitors) did the trick! 
>
> The resistors were well over 100% high in value and the 
> electrolytics had a combination of serious out-of-tolerance 
> values and most had high leakage as well.  

Resistors have a maximum voltage rating - independent of the 
wattage.  The typical resistor of today is rated at a maximum 
of 250 to 350 volts.  This was true years ago too, and 
evidently the Heath engineers never learned this vital fact.  
They calculated wattage and if this was in spec, they forgot 
about the voltage rating.  Thanks to this they lost many color 
TV's.  [One friend of mine went through 4 color picture tubes 
at Heath's expense before they learned this simple lesson.]

In replacing those resistors in the focus and intensity 
circuits, you might consider using several resistors in 
series.  If not, you stand the chance of the new ones failing 
too.

Others here on the list might benefit from this advice too.  
Many early receivers and transmitters seriously went beyond 
the maximum voltage rating specifications of resistors.

        73,  Dr. Barry L. Ornitz     WA4VZQ     ornitz@tricon.net