VAA19419
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>
>At 12:10 PM 2/15/2000 -0700, measures wrote:
>>>
>>>At 07:43 AM 2/15/2000 -0700, measures wrote:
>>>>? However, when the 20m tap on a SB-220 is used for 30m operation, the
>>>>operating Q and the circulating current in the tank increases by c. 40%
>>>> This causes a doubling of the I-squared x R heating in the bandswitch
>>>>contacts. Using the CW tap would help a bit, however, I would not take
>>>>the risk. 220 bandswitches are no longer manufactured.
>>>
>>>On the other hand, if he holds it to the legal 200W power for 30m, the
>>>I-squared part will be pretty small, and the risk probably commensurate.
>>>
>>Decreasing drive and anode current to reduce P-out does not reduce the
>>voltage swing across C-Tune -- if the amplifier is normally tuned for a
>>peak in output. Thus, the AC voltage across C-tune is not decreased by
>>reducing P. (The AC potential across C-tune is the major determiner of
>>tank circulating current -- and this is controlled by the anode supply
>>potential.) .
>
>Oh? So reducing plate current by a factor of 4 doesn't reduce Isquared-R
>heating of the bandswitch by a factor of 16, as I'd expect?
>Seems counterintuitive, but I'll take your word for it unless others beg to
differ.
>
It is only true if the amplifier is tuned up at 250w. If the amplifier
was tuned up at 1000w, and then the drive was reduced to 1/4, there would
be less circulating current through the contacts with reduced drive. .
cheers, Pete N4ZR
>
>Don't forget to update your entry in the World Contest Station Database
>http://206.102.70.3/search.htm
>
>
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>
- Rich..., 805.386.3734, www.vcnet.com/measures.
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