Topband: SB-1000

[Herbert Schoenbohm]

Tom is correct as usual but if you want to get the rig working for the 
Stew coming up a junk box substitute may get you on the air until the 
exact replacement arrives.

Herb, KV4FZ

On 12/21/2015 10:21 AM, Tom W8JI wrote:
>
>
>> If you can't find the exact value of 170pf  the ceramic 5KV door 
>> knobs at 200pf will work.  Better yet even a couple of 500pf door 
>> knobs in series will give you 250 pf which will just mean a little 
>> less on your variable will tune.  Another common ceramic door knob 
>> value is 500pf and three in series will put you in the ball park.
>
> NO.
>
> 170 pF was used because at 200 pF the capacitor breaks over into a 
> different temperature coefficient. You will go from a N750 or so TC to 
> up near or above N2000.
>
> This will make the tuning drift with temperature.
>
> Use the original part or parallel smaller values with the same or 
> lower TC's. Also be ware the number on the case is often not met. 
> Sometimes the caps cannot meet the stamped TC numbers. This is because 
> the clay formula used is difficult to make temperture stable.
>
> Just buy the correct part.
>
> _________________
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