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.
73, Pete N4ZR
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