>Rich says:
>
>>The 160m tank padders in the 77SX have high temperature drift and
>>they are used above their current rating.
>
>It is arguable that if the capacitors get hot, they are being used above
>their current rating.
A friend has a 77SX. He asked me what was the reason for the tank drift
on 160m. The reason(s) turned out to be that the tank padders were being
used above their stated current ratings and they were bypass/coupling
types instead of tuned-circuit types. Since rms tank circulating-current
=s approx. Q x Anode-current, the tank circulating-current in a 77SX is
2A x 10? = 20A-rms. Since c. 40% of this current passes through the
Tune-C padder cap at 1.8MHz, the cap is being operated at several times
its current rating - so it gets quite hot.
cheers, Peter
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
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