>
>
>>2 wrote:
>>> Gold sputtering is caused by vhf/uhf parasites.
>>[...]
>>>Overdriven at HF can not cause gold sputtering. AT UHF, maybe.
>>
>>How do you know that? If there is a difference due to frequency, what is
>>the physical reason for it?
>>
>** note: The "letter about parasitics" Mr. Foote refers to mentioned
>that the resistance of the 8875s; VHF parasitic suppressor resistors had
>changed from 100-ohms to over 400-ohms in a period so brief that the
>outside of the resistors showed no sign of overheating. Richard Kaller,
>W7MOI suggested that such a phenomenon might be caused by a brief VHF
>parasitic oscillation because each resistor was virtually shorted at HF
>by c. 0.07uH of L..
> In a telephone conversation, Mr. Foote said that the gold sputtering
>problem was encountered during the 8877's development. After autopsying
>a leaky tube, the 8877 project engineers concluded that thin layers of
>gold were evaporating during brief bursts of a high frequency oscillation
>condition. I agree since I have seen this problem in a number of
>autopsied 8877s. My guess is that the frequency of oscillation could
>well be above 300MHz, where the 0.1pF of feedback is c. 53-ohms.
> To address your question: Considering that the stored energy in a
>typical amp's filter cap is c. 150-ohms, ... ..
Bozo Alert: This should have been 150-Joules. sorry
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
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