On Tue, 13 May 97 11:56:36 -0700 Rich Measures <measures@vc.net> writes:
>>Rich, your test seems to infer that VHF oscillation is the only thing
>>that could cause a substantial increase in Rs. Is that the case? If
>>so , is there a discussion somewhere that could be read?
>>
>>cheers, Paul
>>ve7cqk
>external heating and a large change in resistance. This happens fast.
> A
>'big-bang' is often heard. I have seen 100 ohm 5% carbon-comp. Rs
>resistors that measured over 400 ohms--yet appeared to be in good
>condition. OTOH, Rs can be burned out completely by VHF energy.
> Since Rs can be completely burned out by either VHF or HF energy, it
>is
>technoblatherous to state that only VHF damage can cause a substantial
>
>increase in R. . However, a substantial increase in R with no
>external
>signs of damage is probably VHF-related.
>Rich---
You and Tom are still failing to follow this thru Rich. The same
resistance increase, but due to skin effect and chemical changes, is a
primary cause of blown filaments in 811A/572B's .
The VHF parasitic is a primary player in this instance...I will have to
agree with your premise with the above tubes.
As I have said to Tom, I will say to you and others. The voltage in a VHF
parasitic is very much dependent upon the unloaded Q of the tank circuit
since the load IS NOT absorbing the energy. Even in a basic 811A circuit
this can exceed the tubes breakdown voltage by many times....20+ KV is
common. Just run the math.
Any BS to the contrary and the refusal to admit to the destructive energy
in a parasitic is irresponsible IMO. Granted, parasitics can take many
forms and many are not destructive; it IS ALL dependendent upon how much
of a real load it sees. We see them as anywhere from an occassional
spitting to a catastrophic BANG.
73....Carl KM1H
>
>R. L. Measures, 805-386-3734, AG6K
>
>
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