> To: amps@contesting.com
> From: km1h@juno.com (km1h @ juno.com)
> I have brought this point up many times here...I'll try AGAIN.
>
> A 2W carbon resistor will show a gradual and steady R increase when run
> above 1W or so....this is at DC.
Amen Carl. That's why carbon resistors should NEVER be used in power
supplies across electrolytics.
> At RF, the heating usually occurs in the 10-15M range, depending upon the
> tubes used and the suppressor design.
> At RF the 2W carbon can double, triple, etc. in value in a few minutes
> or over several years...again it all depends on the design.
Once again VERY true. That is a natural characteristic of the
resistor. You have to NEVER run the resistor close to its rating, or
in a very hot environment unless you use a specified quality of
carbon resistor.
> My own rule of thumb is that 300-400W is the maximum RF on 10M per 2W
> carbon for reasonable long term suppressor reliability. If you have more
> RF then double or triple up the wattage or switch over to a modern metal
> oxide.
Most metal oxides are inductive, be very careful using them.
> IMO, the 2W carbon will quickly become obsolete.
It's on the way, and so are tubes.
73, Tom W8JI
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